# Dr. Jorge Querol > Senior Researcher & Head of 6GSPACE Lab at SnT, University of Luxembourg | Space Technology Expert, Entrepreneur & Independent Consultant - **Full Machine-Readable Knowledge Base (`llms-full.txt`)**: [https://jorge.querol.org/llms-full.txt](https://jorge.querol.org/llms-full.txt) - **Official Website**: [https://jorge.querol.org/](https://jorge.querol.org/) - **Downloadable Executive CV (PDF)**: [https://jorge.querol.org/uploads/resume.pdf](https://jorge.querol.org/uploads/resume.pdf) ## About Dr. Jorge Querol (also indexed in early bibliographic records as **Jorge Querol Borràs** / **J. Querol Borras**) is a Senior Researcher and Head of the [6GSPACE Lab](https://6gspacelab.uni.lu) at the Interdisciplinary Centre for Security, Reliability and Trust ([SnT](https://www.uni.lu/snt-en/)), University of Luxembourg, within the Signal Processing and Communications (SIGCOM) research group. He leads a team of 40+ researchers advancing **6G Non-Terrestrial Networks (NTN)**, **AI-accelerated satellite communications**, **Joint Communications, Sensing and Positioning (JCAS/JCAP)**, **GNSS anti-jamming & RF interference mitigation**, and **quantum/optical space communications**. He is also co-founder of **MITIC Solutions S.L.** (UPC-BarcelonaTech deep-tech spin-off) and an **Independent Technical Consultant** for space agencies, satellite operators, telecom vendors, and defense organizations. ## Key Metrics (Verified 2026) - **40+ Researchers Managed** at the 6GSPACE Lab (SnT, University of Luxembourg) - **180 Scientific Publications** (50+ peer-reviewed journal articles in IEEE JSAC, Proc. IEEE, IEEE TCOMM, IEEE TVT, IEEE JSTARS, IEEE OJCOMS; 125+ conference papers, preprints & theses) - **4,100+ Citations**, **h-index 25** (Google Scholar) - **€9.8M+ Competitive R&D Funding Secured** (Principal Investigator of 11 projects, Vice-PI/Co-Lead of 12 more) - **1 US Granted Patent** (`US9596610B1` – Real-time RF interference detection and mitigation system) ## Core Research & Consulting Pillars 1. **6G Non-Terrestrial Networks (NTN)**: 3GPP Rel-17/18/19+ 5G/6G NR over LEO/MEO/GEO, Direct-to-Device (D2D), TDD/FDD guard-period optimization, Holographic MIMO, and multi-orbit connectivity. 2. **AI-Driven Anti-Jamming & Interference Countermeasures**: Pre-correlation RFI excision, GNSS jamming/spoofing resilience, microwave radiometry protection, and neuromorphic/spiking neural network onboard processing. 3. **Joint Communications, Sensing & Positioning (JCAS / JCAP)**: Multi-Functional Satellite Systems (MFSS Levels 1–4), bistatic radar using LEO Signals of Opportunity (Starlink iSoOp-R), and hybrid GNSS-5G PNT. 4. **Quantum & Optical Space Infrastructure**: Free-Space Optical (FSO) links, structured-light Orbital Angular Momentum (OAM) Quantum Key Distribution (QKD), and Cassegrain optical terminals. ## Key Pages - [About & Homepage](https://jorge.querol.org/) - [Independent Technical Consulting Services](https://jorge.querol.org/consulting/) - [Competitive R&D Projects Portfolio (17 Flagship Projects)](https://jorge.querol.org/projects/) - [Full Publications Archive (180 Papers with Abstracts & DOIs)](https://jorge.querol.org/publication/) - [6GSPACE Lab Team & PhD Supervision](https://jorge.querol.org/supervision/) - [Professional Experience, Education & Awards](https://jorge.querol.org/experience/) - [Graduate Teaching Activities](https://jorge.querol.org/teaching/) - [Download Full 2026 Executive CV (PDF)](https://jorge.querol.org/uploads/resume.pdf) - [Full LLM Knowledge Base (Markdown)](https://jorge.querol.org/llms-full.txt) ## Talks, Tutorials & Presentations (Slide Decks) - [TDD in 5G LEO Satellite Networks: A Comparative Study of Guard-Period Strategies and Frame Durations (Ka and Broadband Communications Conference 2026, Milan, Oct 2026)](https://jorge.querol.org/uploads/talks/2026-10-ka-conf-tdd-leo.pdf) - [Turning 6G Satellites into Sensors: Joint Communications and Sensing in Non-Terrestrial Networks (Invited Lecture, Aalborg University, Oct 2026)](https://jorge.querol.org/uploads/talks/2026-10-aalborg-jcas-ntn.pdf) - [An Overview of 6G Multi-Functional Satellite Systems for Communication, Sensing and Positioning (Tutorial, ASMS 2025, Feb 2025)](https://jorge.querol.org/uploads/talks/2025-02-asms-6g-mfss-tutorial.pdf) - [Luxembourgish Activities on B5G/6G-NTN (Invited Talk, ETSI Conference on Non-Terrestrial Networks, Apr 2024)](https://jorge.querol.org/uploads/talks/2024-04-etsi-b5g-6g-ntn.pdf) - [Challenges in 6G Multi-Satellite Connectivity (Invited Talk, SCSS 2023, Oct 2023)](https://jorge.querol.org/uploads/talks/2023-10-scss-multi-satellite-connectivity.pdf) ## External Profiles & Identifiers - **Google Scholar**: https://scholar.google.com/citations?user=X9C6Pk0AAAAJ - **ORCID**: https://orcid.org/0000-0002-8500-5534 - **LinkedIn**: https://www.linkedin.com/in/jorgequerol - **ORBiLu (University of Luxembourg Open Access)**: https://orbilu.uni.lu/profile?uid=50033359 - **ResearchGate**: https://www.researchgate.net/profile/Jorge-Querol - **GitHub**: https://github.com/jorgequerol - **6GSPACE Lab**: https://6gspacelab.uni.lu - **Contact**: jorge@querol.org | jorge.querol@uni.lu --- ## Independent Space & Telecommunications Consulting Services (`/consulting/`) Dr. Jorge Querol provides independent technical consulting and advisory services registered under the laws of Luxembourg (`jorge@querol.org`): 1. **6G Non-Terrestrial Networks (NTN) & SatCom Systems**: 3GPP 5G/6G NR NTN stack adaptation, multi-orbit LEO/MEO/GEO constellations, Direct-to-Device (D2D) connectivity, TDD guard-period optimization, and JCAS payload engineering. 2. **Anti-Jamming, RFI Excision & GNSS Security**: Patented pre-correlation interference excision (`US9596610B1`), GNSS anti-jamming/anti-spoofing, and microwave radiometer protection. 3. **Onboard AI & SDR Testbed Prototyping**: COTS neuromorphic/NPU onboard satellite processing, USRP/FPGA SDR transceivers, and OpenAirInterface 5G-NTN testbeds. 4. **R&D Strategy, Proposals & Technical Audits**: ESA ARTES / Horizon Europe proposal writing, technical due diligence, link budget verification, and fractional CTO advisory. --- ## Competitive R&D Projects Portfolio (17 Flagship Projects, €9.8M+ Total Funding) - **CREST-5G – TDD & Guard-Period Optimization in 5G NR LEO Satellite Networks** (2025–2027 | European Space Agency (ESA ARTES 4.0) | Role: PHY Lead | Contract 4000147108/25/NL/RA): Time-Division Duplex (TDD) frame design, Adaptive Per-UE guard-period sizing, and Extraordinary Downlink (xDL) guard reuse with OQ Technology SARL. URL: https://jorge.querol.org/project/crest-5g/ - **SMS2 – Sustainable Multi-Functional Satellite Systems** (2025–2028 | FNR Luxembourg (CORE) | Role: Principal Investigator (PI) | €787,000): Coexistence and joint waveform optimization of communications, radar sensing, and positioning payloads on shared satellite hardware and spectrum. URL: https://jorge.querol.org/project/sms2/ - **COSMIC – Direct-to-Device Communications in Mobile Satellite Systems** (2025–2028 | FNR Luxembourg (5G BRIDGES) | Role: Principal Investigator (PI) | €692,000): Channel modeling, compact terminal antenna prototyping, and over-the-satellite field demonstration for C-band Direct-to-Device (D2D) connectivity with SES. URL: https://jorge.querol.org/project/cosmic/ - **Q-LIMIT – Quantum with Structured Lights in Military Telecommunication** (2025–2027 | FNR Luxembourg (CyberHub) | Role: Principal Investigator (PI) | €499,000): Resilient Free-Space Optical (FSO) Quantum Key Distribution (QKD) using structured light orbital angular momentum (OAM) modes for defense networks. URL: https://jorge.querol.org/project/q-limit/ - **5G-Nanosatellite – Integrated 5G UE for 3U CubeSat In-Orbit Demonstrator** (2024–2028 | ESA & Altice Labs | Role: Principal Investigator (PI) | €542,000): Miniaturized 3GPP 5G NR User Equipment terminal payload fitted into a 3U CubeSat mission for live in-orbit validation of direct satellite-to-ground links. URL: https://jorge.querol.org/project/5g-nanosatellite/ - **ATLAS – Autonomous Systems for Land, Air and Space** (2024–2029 | FNR Luxembourg (IPBG) | Role: Principal Investigator (PI) | €288,000): Cross-border 5G/6G UAV connectivity, non-terrestrial satellite backhauling, and autonomous multi-domain vehicle coordination. URL: https://jorge.querol.org/project/atlas/ - **5G-EMERGE – Satellite-Enhanced Edge Delivery** (2024–2026 | European Space Agency (ESA ARTES) | Role: Principal Investigator (PI) | €460,000): 5G Multicast and Broadcast Services (5MBS) demonstration over GEO and LEO satellite networks for intelligent edge caching and vehicular delivery. URL: https://jorge.querol.org/project/5g-emerge/ - **6G-SPACELAB – 6G Non-Terrestrial Networks Experimental Testbed Infrastructure** (2023–2027 | University of Luxembourg / SnT | Role: Principal Investigator (PI) | €1,250,000): Flagship hardware-in-the-loop laboratory infrastructure for 5G/6G satellite communications, OpenAirInterface NTN emulation, and SDR prototyping. URL: https://jorge.querol.org/project/6g-spacelab/ - **LUQCIA – Luxembourg Quantum Communication Infrastructure** (2023–2026 | European Commission (DEP) & SMC | Role: Work Package Lead / Co-PI | €2,000,000+): National terrestrial and satellite-ready Quantum Key Distribution (QKD) infrastructure for ultra-secure government and financial communications. URL: https://jorge.querol.org/project/luqcia/ - **TRANTOR – 5G+ Evolution for Space & Non-Terrestrial Networks** (2023–2025 | European Commission (Horizon Europe) | Role: Work Package Lead / Co-PI | €577,000): Dynamic multi-orbit resource management, AI-driven beam hopping, and 3GPP Release 18/19 NTN constellation orchestration. URL: https://jorge.querol.org/project/trantor/ - **ETHER – sElf-evolving terrestrial/non-Terrestrial Hybrid nEtwoRks** (2023–2025 | European Commission (Horizon Europe) | Role: Co-PI (SnT) | €612,000): Unified 6G 3D architecture integrating terrestrial, aerial (HAPs/UAVs), and spaceborne networks with AI-native zero-touch management. URL: https://jorge.querol.org/project/ether/ - **SPAICE – AI in and for Space – Neuromorphic Onboard Processing** (2022–2024 | European Space Agency (ESA) | Role: Principal Investigator (PI) | €350,000): Spiking Neural Networks (SNNs) and neuromorphic hardware accelerators for ultra-low-power onboard satellite payload beamforming and interference mitigation. URL: https://jorge.querol.org/project/spaice/ - **5G-LEON – 5G Low Earth Orbit Network Demonstrator** (2022–2024 | European Space Agency (ESA ARTES) | Role: Principal Investigator (PI) | €400,000): End-to-end 3GPP 5G NR physical and MAC layer adaptation for high-Doppler LEO satellite links using OpenAirInterface. URL: https://jorge.querol.org/project/5g-leon/ - **JuliaSatSim – High-Performance Satellite Constellation Simulator in Julia** (2023–2025 | ESA / Industry | Role: Principal Investigator (PI) | €250,000): Next-generation parallelized link-and-system-level simulator for mega-constellations and multi-functional 6G satellite networks. URL: https://jorge.querol.org/project/juliasatsim/ - **AVATAR – Adaptive Beamforming & Antenna Array Validation for NTN** (2022–2024 | European Space Agency (ESA) | Role: Co-PI | €450,000): Active phased-array calibration, digital beamforming, and UAV-assisted far-field antenna pattern characterization. URL: https://jorge.querol.org/project/avatar/ - **NGSO-SENSE – Non-Geostationary Orbit Spectrum Sensing & Interference Localization** (2021–2023 | European Space Agency (ESA) | Role: Principal Investigator (PI) | €320,000): Real-time RF interference detection, classification, and geolocation for NGSO satellite uplinks and downlinks. URL: https://jorge.querol.org/project/ngso-sense/ - **PROSPECT – Pre-Correlation RFI Excision for Spaceborne Radiometers & GNSS** (2020–2023 | European Space Agency (ESA) | Role: Co-PI | €380,000): Digital time-frequency and wavelet-domain interference mitigation for Earth observation microwave radiometers and navigation receivers. URL: https://jorge.querol.org/project/prospect/ --- ## Complete Scientific Bibliography (180 Publications, Reverse Chronological Order) 1. **TDD in 5G LEO Satellite Networks: A Comparative Study of Guard-Period Strategies and Frame Durations** (2026) — Madyan Alsenwi, Jorge Querol, Eva Lagunas. In *Ka and Broadband Communications Conference 2026*. URL: https://jorge.querol.org/publication/tdd-in-5g-leo-satellite-networks-2026/ - *Abstract*: This paper presents a comparative study of guard-period (GP) sizing rules (Worst-RTT, Adaptive Per-UE, and Minimum-RTT) and Extraordinary Downlink (xDL) guard-period reuse across 10–182 ms frame durations for Time-Division Duplex (TDD) in 5G NR Low Earth Orbit (LEO) satellite networks, supported by the European Space Agency (ESA) ARTES 4.0 Project CREST-5G. 2. **Joint 5G NR-NTN and GNSS Overlay in MEO: Experimental Assessment of Navigation Data Robustness under DSSS–OFDM Coexistence** (2026) — Idir Edjekouane, Alejandro Gonzalez Garrido, Jevgenij Krivochiza, Jorge Querol, Symeon Chatzinotas. In *Proceedings of the Satellite Division's International Technical Meeting (Online)/Proceedings of the Satellite Division's International Technical Meeting (CD-ROM)*. | DOI: https://doi.org/10.33012/2026.20684 URL: https://jorge.querol.org/publication/joint-5g-nr-ntn-and-gnss-overlay-in-meo-experiment-2026/ - *Abstract*: Recent advances in Joint Communication and Positioning (JCAP) motivate the integration of navigation signals within communication waveforms. This paper investigates a hybrid Direct-Sequence Spread Spectrum (DSSS)–Orthogonal Frequency-Division Multiplexing (OFDM) waveform in which a low-power legacy Global Positioning System (GPS) L1 Coarse/Acquisition (C/A) signal carrying the Legacy Navigation Message (LNAV) message is intentionally overlaid on a Fifth Generation (5G) New Radio (NR) Non-Terrestrial Network (NTN) downlink. The focus is on the Global Navigation Satellite System (GNSS)-side ability to acquire, track, and demodulate the navigation message in the presence of structured 5G interference. The study considers a Medium Earth Orbit (MEO) scenario representative of the SES O3b mPOWER constellation at an altitude of approximately 8000 km. First, MEO Doppler dynamics are characterized using representative orbital parameters, and Monte Carlo (MC) simulations are performed to evaluate LNAV recovery versus Signal-to-Interference-plus-Noise Ratio (SINR) for different transmitted Signal-to-Interference Ratio (SIR) levels. Performance is assessed using navigation-centric metrics, including Bit Error Rate (BER), valid 6 s subframe decoding, valid decoding of the first three subframes, and complete 30 s LNAV frame recovery. The same 35 s reference composite waveform is then transmitted in a continuous loop through the SES O3b mPOWER transparent MEO relay. For each tested SIR level, 300 s of baseband In-phase and Quadrature (I/Q) samples are recorded and processed offline using a MATLAB-based GNSS receiver with 5G Synchronization Signal Block (SSB)-assisted frequency initialization. Simulation results show that, in the considered MEO scenario, Doppler dynamics are moderate and do not constitute the dominant limitation; performance is mainly governed by thermal noise and 5G interference. Experimental results demonstrate reliable LNAV recovery down to approximately -25 dB transmitted SIR, while end-to-end recovery becomes unreliable at -30 dB and below. Since the effective received SINR is not directly available, the experimental results are interpreted as practical transmitted-SIR thresholds. 3. **Terahertz Inter-Satellite Links: Motivation, Challenges and Opportunities** (2026) — Chandan Kumar Sheemar, Wali Ullah Khan, Giovanni Iacovelli, Sourabh Solanki, Mert Bayraktar, Jorge Querol, Eva Lagunas, Symeon Chatzinotas. In *arXiv (Cornell University)*. | DOI: https://doi.org/10.48550/arxiv.2609.05973 URL: https://jorge.querol.org/publication/terahertz-inter-satellite-links-motivation-challen-2026/ - *Abstract*: Inter-satellite links (ISLs) are essential to the evolution of next-generation satellite constellations, providing the foundation for low-latency, resilient, and globally scalable connectivity. While low radio-frequency (RF)-based ISLs offer technological maturity, they are increasingly constrained by spectrum scarcity, congestion, and interference. Optical ISLs, on the other hand, deliver unprecedented capacity but demand ultra-precise pointing, suffer from narrow-beam limitations, and are limited to point-to-point links, all of which hinder large-scale deployment, including point-to-multi-point capability. To overcome these limitations, we propose very-high RF terahertz (THz) inter-satellite links (ISLs) as a promising middle-ground solution, merging the ultra-high data rates of optical links with the adaptability, reliability, and relaxed pointing requirements of lower-frequency RF ISLs. However, despite growing interest, research on THz ISLs remains at an early stage, fragmented across isolated studies, and lacking a clear roadmap for practical realization. This paper aims to address this gap by examining the fundamentals of THz ISLs, assessing their potential advantages and key challenges, and identifying the most promising research directions to transform them into a cornerstone of future interconnected mega constellations. 4. **Protocol-Aware Jamming and Self-Play Defense for Active RIS-Assisted UAV Communications** (2026) — Selma Yahia, Ildi Alla, Hossien B. Eldeeb, Marcele O. K. Mendonça, Carla E. García, Jorge Querol, Symeon Chatzinotas. In *IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)*. | DOI: https://doi.org/10.1109/pimrc69400.2026.11711848 URL: https://jorge.querol.org/publication/protocol-aware-jamming-and-self-play-defense-for-a-2026/ - *Abstract*: This research contribution by Selma Yahia, Ildi Alla, Hossien B. Eldeeb, Marcele O. K. Mendonça et al. (2026), published in IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), investigates "Protocol-Aware Jamming and Self-Play Defense for Active RIS-Assisted UAV Communications" within the domains of RFI Mitigation & GNSS Security. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 5. **Satellite and Mobile Network Operator Cooperation Models for Efficient Handover in 6G-TN-NTN** (2026) — Tedros Salih Abdu, Eva Lagunas, Flor Ortiz, Jorge Querol, Joel Grotz, Marcele O. K. Mendonça, Ons Aouedi, Symeon Chatzinotas. In *The 15th EASN International Conference on “Innovation in Aviation & Space Towards Sustainability Today & Tomorrow”*. | DOI: https://doi.org/10.3390/engproc2026133187 | Open Access: https://hdl.handle.net/10993/66732 URL: https://jorge.querol.org/publication/satellite-and-mobile-network-operator-cooperation--2026/ - *Abstract*: Cooperation between satellite and mobile network operators enables the integration of non-terrestrial satellite networks (NTNs) with terrestrial networks (TNs), allowing users to seamlessly switch from Mobile Network Operators (MNOs) to Satellite Network Operators (SNOs) in areas with limited MNO coverage or during high-speed travel. However, mobility issues, such as connection failures, the ping-pong effect, and high interruption times, can occur during these transitions. This paper examines various cooperation models, including roaming and handover protocols, and proposes key enhancements to these models to reduce service interruption time. It also discusses the use of machine learning (ML) techniques to reduce the above mobility issue and increase the success rate of cooperation among network operators. 6. **6G Nanosatellites to Orbit the Edge: Performance Characterization of a COTS-Based 5G NR UE** (2026) — Jacob Gummesson Atroshi, Türker Yilmaz, Srikanth Goli, Jorge Querol, Symeon Chatzinotas. In *Joint European Conference on Networks and Communications & 6G Summit (EuCNC/6G Summit)*. | DOI: https://doi.org/10.1109/eucnc/6gsummit68295.2026.11577574 URL: https://jorge.querol.org/publication/6g-nanosatellites-to-orbit-the-edge-performance-ch-2026/ - *Abstract*: This research contribution by Jacob Gummesson Atroshi, Türker Yilmaz, Srikanth Goli, Jorge Querol et al. (2026), published in Joint European Conference on Networks and Communications & 6G Summit (EuCNC/6G Summit), investigates "6G Nanosatellites to Orbit the Edge: Performance Characterization of a COTS-Based 5G NR UE" within the domains of 6G-NTN, Satellite Communications. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 7. **When 5G NTN Meets GNSS: Tracking GNSS Signals under Overlaid 5G Waveforms** (2026) — Idir Edjekouane, Alejandro Gonzalez-Garrido, Jorge Querol, Symeon Chatzinotas. In *International Conference on Communications*. | DOI: https://doi.org/10.1109/icc59461.2026.11587695 URL: https://jorge.querol.org/publication/when-5g-ntn-meets-gnss-tracking-gnss-signals-under-2026/ - *Abstract*: Global Navigation Satellite Systems (GNSS) provide the backbone of Positioning, Navigation, and Timing (PNT) but remain vulnerable to interference. Low Earth Orbit (LEO) constellations within Fifth-Generation (5G) Non-Terrestrial Networks (NTN) can enhance resilience by jointly supporting communication and navigation. This paper presents the first quantitative analysis of GNSS tracking and navigation message demodulation under a hybrid waveform where a low-power Direct-Sequence Spread Spectrum (DSSS) component is overlaid on an Orthogonal Frequency-Division Multiplexing (OFDM) 5G downlink. We evaluate a minimally modified GNSS receiver that tracks a legacy Global Positioning System (GPS) L1 Coarse/Acquisition (C/A) overlay aligned with 5G frames while treating the 5G waveform as structured interference. Using Monte Carlo simulations under realistic LEO Doppler dynamics, we analyze the Bit Error Rate (BER) of GPS L1 C/A navigation bits and the subframe decoding probability versus Signalto- Interference-plus-Noise Ratio (SINR) for multiple Signalto- Interference Ratios (SIR) and dynamic classes. Results show reliable demodulation across wide SINR ranges for low and medium dynamics, whereas high dynamics impose strict lock limits. These findings confirm the feasibility of Joint Communication and Positioning (JCAP) using a near-legacy GNSS chipset with minimal receiver modifications. 8. **Channel Extrapolation based Downlink Precoding using 5G NR Uplink SRS in LEO Satellite** (2026) — Ashish Kumar Meshram, Sumit Kumar, Ashok Bandi, Jorge Querol, Stefano Andrenacci, Symeon Chatzinotas. In *International Conference on Communications*. | DOI: https://doi.org/10.1109/icc59461.2026.11587772 URL: https://jorge.querol.org/publication/channel-extrapolation-based-downlink-precoding-usi-2026/ - *Abstract*: This research contribution by Ashish Kumar Meshram, Sumit Kumar, Ashok Bandi, Jorge Querol et al. (2026), published in International Conference on Communications, investigates "Channel Extrapolation based Downlink Precoding using 5G NR Uplink SRS in LEO Satellite" within the domains of 6G-NTN, Satellite Communications, Beamforming & MIMO. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 9. **Lightweight Deep Learning-Aided LDPC Decoding for 5G NR UAV Communications** (2026) — Carla E. García, Jorge Querol, Mario R. Camana, Symeon Chatzinotas. In *IEEE Transactions on Aerospace and Electronic Systems*. | DOI: https://doi.org/10.1109/infocom59046.2026.11571367 URL: https://jorge.querol.org/publication/lightweight-deep-learning-aided-ldpc-decoding-for-2026/ - *Abstract*: This research contribution by Carla E. García, Jorge Querol, Mario R. Camana, Symeon Chatzinotas (2026), published in IEEE Transactions on Aerospace and Electronic Systems, investigates "Lightweight Deep Learning-Aided LDPC Decoding for 5G NR UAV Communications" within the domains of 6G-NTN, AI & Neuromorphic SatCom. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 10. **Performance analysis of the Cassegrain telescope on the QKD with Mathieu-Gauss Beams** (2026) — S. Oktay, Mert Bayraktar, Francesco Vista, Jorge Querol, Yves Schmit, S. Chatzinotas. In *Scientific Reports*. | DOI: https://doi.org/10.1038/s41598-026-51915-y | Open Access: https://orbilu.uni.lu/handle/10993/68840 URL: https://jorge.querol.org/publication/performance-analysis-of-the-cassegrain-telescope-o-2026/ - *Abstract*: Mathieu-Gauss beams (MGBs), a distinctive class of structured light generated by modulating the angular and radial components of Gaussian beams with Mathieu functions, exhibit propagation characteristics that make them promising candidates for free-space optical (FSO) and quantum communication links. In this study, the scintillation behaviour of MGBs under weak atmospheric turbulence is analysed to derive the effective visibility and to quantify its impact on the quantum bit error rate (QBER) and secret key rate (SKR) in quantum key distribution (QKD) systems employing Cassegrain-type transmitters. Numerical simulations are performed using a random phase screen method based on the modified von Kármán spectrum for even and odd MGB modes under various telescope configurations. QBER is modelled as a function of effective visibility derived from the scintillation index. The results demonstrate that the use of a Cassegrain telescope significantly suppresses scintillation-induced degradation, reduces QBER, and enhances SKR, with improvements of up to 80% compared to free-space propagation without telescopic correction. However, the performance enhancement is strongly mode-dependent, with certain MGB orders exhibiting greater turbulence resilience. These findings highlight the importance of transmitter geometry and beam-structure optimisation in improving the robustness and efficiency of structured-light-based FSO-QKD systems. 11. **High-Accuracy Ranging in 5G Non-Terrestrial Networks: Receiver Architectures and Interference Analysis** (2026) — Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, José A. del Peral-Rosado, Ivan Lapin. In *IEEE Transactions on Vehicular Technology*. | DOI: https://doi.org/10.1109/navitec202669090.2026.11692531 URL: https://jorge.querol.org/publication/high-accuracy-ranging-in-5g-non-terrestrial-networ-2026/ - *Abstract*: This research contribution by Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, José A. del Peral-Rosado et al. (2026), published in IEEE Transactions on Vehicular Technology, investigates "High-Accuracy Ranging in 5G Non-Terrestrial Networks: Receiver Architectures and Interference Analysis" within the domains of 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 12. **Collaborative Multi-Band Multi-Orbit 6G Satellites with Multi-Connectivity: The Roles of Carrier Aggregation and Dual Connectivity** (2026) — Mohammed Al-Ansi, Jorge Querol, Eva Lagunas, Madyan Alsenwi, Symeon Chatzinotas. In *IEEE Communications Magazine*. | DOI: https://doi.org/10.1109/mcom.001.2500337 | Open Access: https://orbilu.uni.lu/handle/10993/68343 URL: https://jorge.querol.org/publication/collaborative-multi-band-multi-orbit-6g-satellites-2026/ - *Abstract*: Non-terrestrial networks (NTNs), particularly satellites, are increasingly being recognized as vital components beyond complementing terrestrial networks (TNs) in unified TN-NTN 6G systems. However, satellites operate independently in their orbits with single frequency bands, facing performance limitations that hinder their ability to satisfy diverse requirements. This has driven interest in transitioning from singleband single-orbit to multi-band multi-orbit (MBMO) systems, leveraging spectral and orbital diversities. This article emphasizes the significance of MBMO and presents multi-connectivity (MC) as an effective approach enabling collaboration across bands and orbits. We focus on carrier aggregation (CA) and dual connectivity (DC), two essential enablers of MC at different levels of the 3GPP protocol stack. We discuss their principles, benefits, and usage scenarios along with two case studies. A Ku-Ka inter-band CA case study demonstrated gains in throughput and reliability, ensuring service continuity under adverse weather conditions for a multi-band geostationary orbit (GEO) system. A multi-orbit DC between GEO and low Earth orbit (LEO) shows how DC addresses LEO satellite mobility challenges through seamless handovers. We also outline some open issues that require further study and advancement. 13. **Hybrid Deep Learning Decoder for Satellite Communication Systems** (2026) — Carla E. García, Mario R. Camana, Marcele O. K. Mendonça, Jorge Querol, Symeon Chatzinotas. In *IEEE Wireless Communications and Networking Conference Workshops (WCNCW)*. | DOI: https://doi.org/10.1109/wcncw67598.2026.11555163 URL: https://jorge.querol.org/publication/hybrid-deep-learning-decoder-for-satellite-communi-2026/ - *Abstract*: This research contribution by Carla E. García, Mario R. Camana, Marcele O. K. Mendonça, Jorge Querol et al. (2026), published in IEEE Wireless Communications and Networking Conference Workshops (WCNCW), investigates "Hybrid Deep Learning Decoder for Satellite Communication Systems" within the domains of Satellite Communications, AI & Neuromorphic SatCom. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 14. **Survey on Beyond Diagonal RIS-Enabled 6G Wireless Networks: Fundamentals, Recent Advances, and Challenges** (2026) — Wali Ullah Khan, Chandan Kumar Sheemar, Manzoor Ahmed, Marco Di Renzo, Syed Tariq Shah, Asad Mahmood, Eva Lagunas, Jorge Querol, Symeon Chatzinotas, Zhu Han. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/ojcoms.2026.3734637 | Open Access: https://orbilu.uni.lu/handle/10993/69247 URL: https://jorge.querol.org/publication/survey-on-beyond-diagonal-ris-enabled-6g-wireless-2026/ - *Abstract*: Beyond Diagonal Reconfigurable Intelligent Surfaces (BD-RIS) represent a groundbreaking innovation in sixth-generation (6G) wireless networks, enabling unprecedented control over wireless propagation environments compared to conventional diagonal RIS (D-RIS). This survey provides a comprehensive analysis of BD-RIS, detailing its architectures, operational principles, and mathematical modeling while highlighting its performance benefits. BD-RIS classifications, including single-connected, fully-connected, and group-connected architectures, and their reflective, transmissive, hybrid, and multi-sector operating modes are examined. Recent advances in BD-RIS-enabled 6G networks are reviewed, focusing on critical areas such as channel estimation, sum-rate and spectral efficiency optimization, energy efficiency enhancement, and security. The survey identifies fundamental challenges in BD-RIS research, including hardware design limitations, adaptive channel estimation, and the impact of non-ideal hardware effects. Future research directions for BD-RIS are proposed, emphasizing the integration of artificial intelligence and machine learning (AI/ML), joint optimization of communication and sensing, and enhanced physical layer security (PLS). This study concludes by underscoring BD-RIS's transformative potential to redefine 6G wireless networks, offering valuable insights and lessons for future research and development. 15. **RPDMA: A PAPR-Aware Multiple Access Scheme** (2026) — Goli Srikanth, Shaik Basheeruddin Shah, Nazar T. Ali, Vijay Kumar Chakka, Jorge Querol, Ahmed Altunaiji, Dragan I. Olćan. In *IEEE Open Journal of Vehicular Technology*. | DOI: https://doi.org/10.1109/OJVT.2026.3661153 | Open Access: https://hdl.handle.net/10993/67739 URL: https://jorge.querol.org/publication/rpdma-a-papr-aware-multiple-access-scheme-2026/ - *Abstract*: This paper proposes a novel Multiple Access (MA) scheme called Ramanujan Periodic subspace Division Multiple Access (RPDMA) for subcarrier sizes N = 2m, m ∊ N, to address the high Peak-to-Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiple Access (OFDMA). Building on the properties of Ramanujan subspaces, we design transmitter and receiver models that allocate users on a subspace-wise basis, ensuring zero inter-user interference, providing inherent frequency diversity. We analyze the computational complexity of OFDMA, SC-FDMA, and RPDMA, and find that RPDMA has substantially lower per-user transmitter complexity than both OFDMA and SC-FDMA, while its receiver complexity is comparable to SC-FDMA and higher than that of OFDMA. We further introduce a generalized framework, termed Nested Periodic-subspace Division Multiple Access (NPDMA), which unifies both RPDMA and OFDMA under a common family of multi-carrier MA schemes. We derive the theoretical PAPR of RPDMA and demonstrate its superiority over OFDMA. The analysis is validated through numerical simulations under two multi-user scenarios with diverse Quality of Service (QoS) requirements. The results demonstrate that RPDMA achieves lower PAPR than both OFDMA and SC FDMA, with users assigned larger subspaces benefiting from even greater PAPR reduction. We prove that both the sum and per-user Spectral Efficiency (SE) of RPDMA are identical to those of OFDMA and SC-FDMA. In terms of Bit Error Rate (BER), SC-FDMA achieves the best performance, while RPDMA still outperforms OFDMA as the SNR increases. 16. **RIS-Enabled Joint Communications and Sensing in 6G NTNs: Opportunities and Challenges** (2026) — Wali Ullah Khan, Chandan Kumar Sheemar, Muhammad Ali Jamshed, Eva Lagunas, Jorge Querol, Aryan Kaushik, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2026.3655070 URL: https://jorge.querol.org/publication/ris-enabled-joint-communications-and-sensing-in-6g-2026/ - *Abstract*: The integration of Joint Communications and Sensing (JCAS) and Reconfigurable Intelligent Surfaces (RIS) is poised to be a cornerstone of Sixth-Generation (6G) Non-Terrestrial Networks (NTNs), enabling unprecedented capabilities for ubiquitous connectivity and high-resolution environmental monitoring. While the synergy between RIS and JCAS in terrestrial networks has been explored, its application in the unique and stratified environment of NTNs presents distinct opportunities and challenges across different propagation domains. This paper provides a comprehensive analysis of RIS-enabled JCAS for 6G NTNs, with a specific focus on differentiating the operational landscape between the space layer and the atmospheric layer. We identify novel key opportunities in the atmospheric layer, including uncrewed aerial vehicles (UAVs) and high-altitude platforms (HAPSs), and the space layer, including, low-Earth orbit, medium Earth orbit, and Geostationary orbit (GEO), and present and discuss the future challenges to be addressed to realize the integration of RIS a reality for the next-generation JCAS for NTNs. 17. **Mirage Detector: A Reliable Multiuser Preamble Detector for 6G-NTN** (2026) — Ali Georganaki, Jorge Querol, Thang X. Vu, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2026.3679839 | Open Access: https://hdl.handle.net/10993/68160 URL: https://jorge.querol.org/publication/mirage-detector-a-reliable-multiuser-preamble-dete-2026/ - *Abstract*: Accessing non-terrestrial networks (NTN) via existing 4G/5G handheld devices without positioning information presents significant challenges in achieving precise synchronization between a gNodeB and hundreds of users dispersed across an NTN cell. While terrestrial communication standards limit the relative delay between the center and edge of coverage to 200 km, multilayered NTN can introduce user-specific delay variation spanning thousands of kilometers. To address this challenge, we reeingeer the receiver’s Random Access (RA) preamble detector to achieve robust detection and Transmission Arrival (TA) estimation of scattered users with unknown but deterministic differential delays. The proposed Physical layer algorithm, termedMiragedetector, aligns with current 3GPP NTN standardization efforts and is forward/backward-compatible with future/earlier releases.Miragedetector leverages a dynamicStridingmechanism for multiple hypothesis testing, making it resilient to high false alarm rates caused by signals arriving beyond their nominal duration.Miragealso efficiently supports multiuser detection, enabling rapid resynchronization during frequent handovers—approximately twice per minute per Connected UE—while minimizing computational load of the transceivers. Extensive simulations results validate the advantage of the proposedMiragedetector that enables reliable multilayer connectivity for hundreds of legacy devices within the access occasion periodicity, without requiring hardware upgrades or any self-localization capability. 18. **Joint Beamforming and 3D Location Optimization for Multi-User Holographic UAV Communications** (2026) — Chandan Kumar Sheemar, Asad Mahmood, Christo Kurisummoottil Thomas, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas, Walid Saad. In *IEEE Transactions on Communications*. | DOI: https://doi.org/10.1109/TCOMM.2026.3663285 URL: https://jorge.querol.org/publication/joint-beamforming-and-3d-location-optimization-for-2026/ - *Abstract*: This paper pioneers the domain of multi-user holographic unmanned aerial vehicle (UAV) communications, establishing a robust foundation for future advancements in next-generation aerial wireless networks. It investigates the joint design of hybrid holographic beamforming and three-dimensional (3D) positioning for a UAV equipped with a reconfigurable holographic surface (RHS), with the objective of maximizing the network’s sum rate. To tackle this inherently complex and non-convex optimization problem, a novel alternating optimization framework is proposed. The solution leverages zero-forcing (ZF) digital beamforming and a gradient ascent strategy to iteratively update the holographic beamforming weights and the UAV’s 3D location, while satisfying key system constraints. This framework is tailored to efficiently navigate the trade-offs between hybrid transceiver design and UAV mobility limitations, ensuring both adaptability and performance scalability. Simulation results confirm that the proposed approach achieves substantial gains in sum rate and system robustness compared to conventional methods, validating its effectiveness under diverse channel and deployment conditions. 19. **Intelligent Handover Management for Hybrid TN–NTN Mobility in 6G Architectures** (2026) — Ons Aouedi, Tedros Salih Abdu, Kha Hung NGUYEN, Eva Lagunas, Jorge Querol, Joël Grotz. In *Open Repository and Bibliography (University of Luxembourg)*. | Open Access: https://orbilu.uni.lu/handle/10993/69015 URL: https://jorge.querol.org/publication/intelligent-handover-management-for-hybrid-tnntn-m-2026/ - *Abstract*: This research contribution by Ons Aouedi, Tedros Salih Abdu, Kha Hung NGUYEN, Eva Lagunas et al. (2026), published in Open Repository and Bibliography (University of Luxembourg), investigates "Intelligent Handover Management for Hybrid TN–NTN Mobility in 6G Architectures" within the domains of 6G-NTN. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 20. **Impact of Out-of-Band Emissions From Active Antenna Systems on LEO Satellite Downlink Coexistence in the C-Band** (2026) — Carla E. García, Michael N. Dazhi, Jorge Querol, Eva Lagunas, Mario R. Camana, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/ojcoms.2026.3726684 URL: https://jorge.querol.org/publication/impact-of-out-of-band-emissions-from-active-antenn-2026/ - *Abstract*: The coexistence between terrestrial 5G networks and low Earth orbit (LEO) satellite systems in the C-band has raised increasing concerns due to the aggregated impact of out-of-band emissions (OOBE) from active antenna systems (AAS). This paper investigates the interference generated by terrestrial 5G downlink transmissions toward a ground-based LEO user equipment, with a particular focus on the role of AAS and different transmission schemes. Two operational modes are considered for the 5G remote radio unit (RRU): broadcast transmission, representing wide-coverage signaling with quasi-omnidirectional radiation characteristics, and data transmission, employing user-directed beamformed composite array patterns. A conservative coexistence scenario is analyzed, providing an upper-bound reference, in which multiple 5G RRUs are deployed around a ground LEO user operating in reception mode. In particular, pedestrian and vehicular ground users are considered to capture the impact of antenna characteristics. System-level simulations evaluate the aggregated interference power, interference-to-noise ratio (INR), and link-level metrics such as signal-to-interference-plus-noise ratio (SINR) and signal-to-noise ratio (SNR) under varying user distances, network densities, and satellite off-boresight angles. These findings highlight the importance of accounting for network densification and antenna pattern effects in C-band coexistence studies and regulatory assessments involving LEO satellite systems. 21. **Holographic Mimo for Next-Generation Nonterrestrial Networks: Motivation, Opportunities, and Challenges** (2026) — Giovanni Iacovelli, Chandan Kumar Sheemar, Wali Ullah Khan, Asad Mahmood, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas. In *IEEE Vehicular Technology Magazine*. | DOI: https://doi.org/10.1109/MVT.2026.3673016 URL: https://jorge.querol.org/publication/holographic-mimo-for-next-generation-nonterrestria-2026/ - *Abstract*: In this article, we propose the integration of the holographic multiple-input multiple-output (HMIMO) as a transformative solution for next-generation nonterrestrial networks (NTNs), addressing key challenges, such as high hardware costs, launch expenses, and energy inefficiency. Traditional NTNs are constrained by the financial and operational limitations posed by bulky and costly antenna systems, alongside the complexities of maintaining effective communications in space. HMIMO offers a novel approach utilizing compact and lightweight arrays of densely packed radiating elements with real-time reconfiguration capabilities, thus capable of optimizing system performance under dynamic conditions such as varying orbital dynamics and Doppler shifts. By replacing conventional antenna systems with HMIMO, the number of required radio-frequency (RF) chains can be cut to roughly one-tenth while achieving about threefold lower power consumption and an order-of-magnitude decrease in hardware cost. Thus, manufacturing and launch expenses can be substantially reduced, paving the way for more streamlined and cost-effective NTN deployments. This advancement holds significant potential to democratize space communications, making them accessible to a broader range of stakeholders, including smaller nations and commercial enterprises. Moreover, the inherent capabilities of HMIMO in enhancing energy efficiency, scalability, and adaptability position this technology as a key enabler of new use cases and sustainable satellite operations. 22. **Holographic Joint Communications and Sensing With Cramér-Rao Bounds** (2026) — Chandan Kumar Sheemar, Wali Ullah Khan, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas. In *IEEE Journal on Selected Areas in Communications*. | DOI: https://doi.org/10.1109/JSAC.2025.3613282 | Open Access: https://hdl.handle.net/10993/66699 URL: https://jorge.querol.org/publication/holographic-joint-communications-and-sensing-with--2026/ - *Abstract*: This research contribution by Chandan Kumar Sheemar, Wali Ullah Khan, George C. Alexandropoulos, Jorge Querol et al. (2026), published in IEEE Journal on Selected Areas in Communications, investigates "Holographic Joint Communications and Sensing With Cramér-Rao Bounds" within the domains of JCAS & Earth Observation, Beamforming & MIMO. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 23. **Automatic RFI Detection, Location, and Classification System in GNSS Bands** (2026) — Adrián Pérez-Portero, Jorge Querol, Adriano Camps. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing*. | DOI: https://doi.org/10.1109/JSTARS.2025.3647776 | Open Access: https://hdl.handle.net/10993/67073 URL: https://jorge.querol.org/publication/automatic-rfi-detection-location-and-classificatio-2026/ - *Abstract*: Global Navigation Satellite Systems (GNSS) are critical infrastructure components in modern Positioning, Navigation, and Timing (PNT) services, playing a vital role in both civilian and defense applications. These systems operate in specific frequency bands that are also utilized by other Earth Observation technologies, such as GNSS-Radio Occultations and GNSS-Reflectometry. Other passive microwave remote sensing techniques such as microwave radiometers, work with very faint signals in nearby frequency bands within the L-Band. However, the increasing prevalence of Radio-Frequency Interferences (RFI) poses a significant threat, potentially compromising the integrity and reliability of PNT services, and corrupting geophysical observations. Effective RFI mitigation relies on accurate detection and classification of interference sources, a task that becomes increasingly challenging due to the complexity and diversity of RFI signals. This work presents an automated classification system for RFI detection and characterization in GNSS bands. The methodology employs advanced digital signal processing techniques and statistical algorithms to improve RFI detection and classification. RFI events are then stored in a long-term database to provide insights into the local spectrum, and to aid in mitigation and law enforcement efforts. This study provides a description of the classification system, including its architecture, implementation, and performance analysis. The results highlight the potential of this system to enhance the resilience of GNSS PNT services against RFI. 24. **Intelligent Multi-Connectivity and Resource Allocation Framework for LEO Satellite Networks** (2025) — Madyan Alsenwi, Eva Lagunas, Jorge Querol, Yan Kyaw Tun, Symeon Chatzinotas. In *IEEE Globecom Workshops (GC Wkshps)*. | DOI: https://doi.org/10.1109/gcwkshps68340.2025.11591030 | Open Access: https://orbilu.uni.lu/handle/10993/66147 URL: https://jorge.querol.org/publication/intelligent-multi-connectivity-and-resource-alloca-2025/ - *Abstract*: Low Earth Orbit (LEO) satellite networks are expected to play a key role in extending global 6G coverage. However, their dynamic topology and limited radio resources present significant challenges to reliable and efficient user access. One promising solution is multi-connectivity, where a user connects to multiple visible satellites simultaneously to improve link robustness and throughput. In particular, the efficient operation of multi-connectivity in LEO networks depends on making coordinated decisions about satellite-user links and how available spectrum resources are distributed. In this paper, we formulate an optimization problem to jointly optimize user association with multi-connectivity options and resource block (RB) allocation, considering the dynamic and uncertain nature of LEO satellite networks. To solve this problem, we propose a deep reinforcement learning (DRL) framework that learns to make decisions based on global network observations. Specifically, a DRL agent, deployed at a terrestrial central controller with global network visibility, learns to allocate RBs and select multi-connectivity links to maximize network throughput and ensure user Quality-of-Service (QoS). The proposed approach leverages inter-satellite communication links (ISLs) to forward network state information from satellites to the central ground agent and to relay the agent’s decisions back to satellites that do not have direct connectivity to the ground Gateway (GW) stations. Simulation results confirm the effectiveness of the proposed framework in improving data rates in dynamic LEO environments. 25. **Effect of the Cassegrain Telescope on the scintillation of Mathieu-Gauss beams** (2025) — Mert Bayraktar, Francesco Vista, Jorge Querol, Yves Schmit, Symeon Chatzinotas. In *IEEE International Conference on Space Optical Systems and Applications (ICSOS)*. | DOI: https://doi.org/10.1117/12.3063944 | Open Access: https://orbilu.uni.lu/handle/10993/66155 URL: https://jorge.querol.org/publication/effect-of-the-cassegrain-telescope-on-the-scintill-2025/ - *Abstract*: The scintillation index plays a crucial role in the performance of free space optics (FSO) and quantum key distribution (QKD) systems. Enhancement in the scintillation index causes an increase in the bit error rate and a decrease in the key rate. In this paper, we studied the effect of the Cassegrain telescope on the scintillation of Mathieu-Gauss beams (MGB) in a weak turbulent atmosphere. We model the atmosphere by using the random phase screen numerical approach. We benefit from the hard aperture function when modeling the telescope. We compare the point-like scintillation values with and without the Cassegrain telescope. We research even and odd modes of the MGB. We observe that the scintillation index decreases drastically when using the Cassegrain telescope. In addition, we investigate that the scintillation index decreases when the expansion order rises. Similarly, we see that there is an inverse relation between the first complex expansion coefficient at a short distance. An increase in the second complex expansion coefficient shows its advantage at longer distances by mitigating scintillation. We anticipate that our results will be useful for the optical engineers to design FSO and QKD systems. 26. **Optimized Satellite Participation in Federated Learning over LEO Constellation Networks** (2025) — Madyan Alsenwi, Eva Lagunas, Jorge Querol, Mohammed Al-Ansi, Dinh-Hieu Tran, Yan Kyaw Tun, Symeon Chatzinotas. In *IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)*. | DOI: https://doi.org/10.1109/pimrc62392.2025.11275527 | Open Access: https://orbilu.uni.lu/handle/10993/66149 URL: https://jorge.querol.org/publication/optimized-satellite-participation-in-federated-lea-2025/ - *Abstract*: This paper presents an intelligent device selection framework for Federated Learning (FL) in Low Earth Orbit (LEO) satellite constellation networks. In particular, the high mobility, intermittent connectivity and long communication delays in LEO satellite networks significantly impact FL convergence and model performance. To address these challenges, we formulate a device selection optimization problem that determines the optimal subset of LEO satellites to participate in global model aggregation at each round. The objective is to minimize the average loss while satisfying latency constraints. To solve the formulated problem, we develop a deep reinforcement learning (DRL)-based solution that enables adaptive satellite selection considering the stochastic nature of satellite connectivity and channel variability. The proposed framework selects participating satellites dynamically based on their communication latency and computational capabilities to improve the overall efficiency of the FL process. Simulation results show that the proposed approach accelerates convergence compared to conventional synchronous FL while maintaining model accuracy. 27. **Greedy User Scheduling and Beamforming for Holographic Communications** (2025) — Chandan Kumar Sheemar, Christo Kurisummoottil Thomas, Wali Ullah Khan, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas, Walid Saad. In *IEEE International Mediterranean Conference on Communications and Networking (MeditCom)*. | DOI: https://doi.org/10.1109/meditcom64437.2025.11104470 URL: https://jorge.querol.org/publication/greedy-user-scheduling-and-beamforming-for-hologra-2025/ - *Abstract*: This paper focuses on the challenge of joint hybrid holographic beamforming and user scheduling while guaranteeing per-user minimum Quality-of-Service (QoS) constraints, a key concern in resource-limited wireless networks. However, this problem leads to a mixed-integer non-convex optimization formulation, making it computationally intractable to solve efficiently using conventional methods. To tackle this complexity, we propose an iterative optimization framework that jointly optimizes holographic beamforming patterns and user scheduling to maximize the sum-rate of RHS-assisted networks. Our approach integrates zero-forcing digital beamforming to mitigate interference, a gradient-ascent-based optimization technique for refining holographic beamforming weights, and a greedy User Scheduling strategy to dynamically allocate resources while meeting QoS constraints. Extensive simulation results confirm the effectiveness of our proposed framework, demonstrating significant improvements in sum-rate performance compared to the benchmark algorithm. 28. **A Machine Learning-Based Receiver for Mitigating Nonlinear Distortion in OFDM Systems for 5G** (2025) — Marcele O. K. Mendonça, Francisco J. Martín Vega, Geoffrey Eappen, Carla E. García, Abuzar B. M. Adam, Jorge Querol, Beatriz Soret, Symeon Chatzinotas. In *IEEE International Mediterranean Conference on Communications and Networking (MeditCom)*. | DOI: https://doi.org/10.1109/meditcom64437.2025.11104481 | Open Access: https://orbilu.uni.lu/handle/10993/66913 URL: https://jorge.querol.org/publication/a-machine-learning-based-receiver-for-mitigating-n-2025/ - *Abstract*: This work introduces a convolutional neural network (CNN)-based receiver designed for channel estimation, equalization, and symbol demapping in orthogonal frequency-division multiplexing (OFDM) systems. The proposed receiver is specifically developed to mitigate nonlinear distortions, particularly under low input back-off (IBO), thereby markedly enhancing signal quality and energy efficiency. By significantly reducing the bit error rate (BER) and outperforming traditional methods, the CNN-based receiver establishes itself as a highly robust solution for next-generation communication technologies. These advancements are pivotal for the development of reliable and efficient communication networks, particularly in the context of the fifth generation (5G) and beyond. Furthermore, this work contributes to the integration of terrestrial and non-terrestrial networks by addressing critical challenges in mitigating nonlinear distortions in satellite and hybrid communication systems using AI-driven techniques. 29. **Machine Learning-Driven Framework for Reducing PAPR in Satellite Communication Systems** (2025) — Carla E. García, Francisco J. Martin Vega, Mario R. Camana, Jorge Querol, Saud Althunibat, Khalid A. Qaraqe, Symeon Chatzinotas. In *IEEE Vehicular Technology Conference*. | DOI: https://doi.org/10.1109/vtc2025-spring65109.2025.11174301 | Open Access: https://orbilu.uni.lu/handle/10993/67071 URL: https://jorge.querol.org/publication/machine-learning-driven-framework-for-reducing-pap-2025/ - *Abstract*: High peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) signals presents a persistent challenge in satellite communications (SatCom), impacting signal quality and causing adjacent channel interference. This paper introduces a novel framework that combines the elastic net-based machine learning (ML) model with the partial transmit sequence (PTS) technique to effectively reduce PAPR. Additionally, the potential of artificial intelligence (AI) approaches are investigated, specifically swarm intelligence and ML methods, for high-performance, low-complexity solutions. In this regard, ML models are applied to mitigate PAPR in SatCom networks under the presence of a traveling wave tube amplifier (TWTA) model and a land mobile satellite (LMS) channel, employing 16-quadrature amplitude modulation (16-QAM). Compared with the baseline schemes, simulation results demonstrate that the proposed ML framework, integrating principal component analysis (PCA) with the elastic net learning model, achieves comparable PAPR performance and minimal computational complexity. 30. **Statistical Acquisition of DVB-S2X Signal for Positioning in LEONTN** (2025) — Harshal More, Idir Edjekouane, Ernestina Cianca, Mauro De Sanctis, Jorge Querol, Ottavio M. Picchi, Francesco Menzione. In *International Conference on Localization and GNSS*. | DOI: https://doi.org/10.1109/icl-gnss65520.2025.11046183 | Open Access: https://orbilu.uni.lu/handle/10993/66125 URL: https://jorge.querol.org/publication/statistical-acquisition-of-dvb-s2x-signal-for-posi-2025/ - *Abstract*: Low Earth Orbit (LEO) mega-constellations are revolutionizing global communication by delivering high-speed internet and supporting a wide range of services. Beyond communication, recent studies have shown that LEO satellites can also provide Positioning, Navigation, and Timing (PNT) services. Leveraging existing LEO Non-terrestrial-network (NTN) for dual-purpose applications has garnered significant attention as a future-oriented approach. This paper investigates the feasibility of re-purposing a well-established satellite communication protocol, Digital Video Broadcasting Second Generation Satellite Extensions (DVB-S2X), for positioning applications within LEONTN. This paper analyses the statistical acquisition performance similar to the Global Navigation Satellite System (GNSS) to evaluate the potential of DVB-S2X for positioning estimation. This analysis can provide a baseline for trade-offs for communication protocol selection when developing a sustainable integrated navigation and communication (Nav-Comm) system within LEONTN. 31. **Artificial Intelligence implementation of onboard flexible payload and adaptive beamforming using commercial off-the-shelf devices** (2025) — Luis Manuel Garcés-Socarrás, Amirhosein Nik, Flor Ortíz, Juan Andres Vásquez-Peralvo, Jorge Luis González Ríos, Mouhamad Chehailty, Marcele Kuhfuss, Eva Lagunas, Jan Thoemel, Sumit Kumar, Singh, Vishal, Juan Carlos Merlano Duncán, Sahar Malmir, Swetha Varadajulu, Jorge Querol, Symeon Chatzinotas. In *arXiv (Cornell University)*. | DOI: https://doi.org/10.48550/arxiv.2505.01853 URL: https://jorge.querol.org/publication/artificial-intelligence-implementation-of-onboard-2025/ - *Abstract*: Very High Throughput satellites typically provide multibeam coverage, however, a common problem is that there can be a mismatch between the capacity of each beam and the traffic demand: some beams may fall short, while others exceed the requirements. This challenge can be addressed by integrating machine learning with flexible payload and adaptive beamforming techniques. These methods allow for dynamic allocation of payload resources based on real-time capacity needs. As artificial intelligence advances, its ability to automate tasks, enhance efficiency, and increase precision is proving invaluable, especially in satellite communications, where traditional optimization methods are often computationally intensive. AI-driven solutions offer faster, more effective ways to handle complex satellite communication tasks. Artificial intelligence in space has more constraints than other fields, considering the radiation effects, the spaceship power capabilities, mass, and area. Current onboard processing uses legacy space-certified general-purpose processors, costly application-specific integrated circuits, or field-programmable gate arrays subjected to a highly stringent certification process. The increased performance demands of onboard processors to satisfy the accelerated data rates and autonomy requirements have rendered current space-graded processors obsolete. This work is focused on transforming the satellite payload using artificial intelligence and machine learning methodologies over available commercial off-the-shelf chips for onboard processing. The objectives include validating artificial intelligence-driven scenarios, focusing on flexible payload and adaptive beamforming as machine learning models onboard. Results show that machine learning models significantly improve signal quality, spectral efficiency, and throughput compared to conventional payload. 32. **Optimizing Antenna Activation for Even Power Distribution in Multi-Beam Satellite Systems Using Genetic Algorithm** (2025) — Juan Andres Vásquez-Peralvo, Aral Ertug Zorkun, Jorge Querol, Eva Lagunas, Flor Ortíz, Luis Manuel Garcés-Socarrás, Jorge Luis González Ríos, Symeon Chatzinotas. In *European Conference on Antennas and Propagation*. | DOI: https://doi.org/10.23919/eucap63536.2025.10999190 | Open Access: https://orbilu.uni.lu/handle/10993/66599 URL: https://jorge.querol.org/publication/optimizing-antenna-activation-for-even-power-distr-2025/ - *Abstract*: Recent advancements in onboard satellite communication have significantly enhanced the ability to dynamically modify the radiation pattern of a Direct Radiating Array (DRA), which is essential for both conventional communication satellites like Geostationary Orbit (GEO) and those in lower orbits such as Low Earth Orbit (LEO). This is particularly relevant for communication at 28 GHz, a key frequency in the mmWave spectrum, used for high-bandwidth satellite links and 5G communications. Critical design factors include the number of beams, beamwidth, and Side Lobe Level (SLL) for each beam. However, in multibeam scenarios, balancing these design factors can result in uneven power distribution, leading to over-saturation in centrally located antenna elements due to frequent activations. This paper introduces a Genetic Algorithm (GA)-based approach to optimize beamforming coefficients by modulating the amplitude component of the weight matrix, while imposing a constraint on activation instances per element to avoid over-saturation in the Radio Frequency (RF) chain. The proposed method, tested on an 16×16 DRA patch antenna array at 28 GHz for a CubeSat orbiting at 500 km, demonstrates how the algorithm efficiently meets beam pattern requirements and ensures uniform activation distribution. These findings are particularly relevant for emerging satellite systems and 5G networks operating in the mmWave spectrum. 33. **Resource Allocation Under Uncertainty in LEO Satellite Constellation Networks** (2025) — Madyan Alsenwi, Eva Lagunas, Jorge Querol, Yan Kyaw Tun, Symeon Chatzinotas. In *IEEE Wireless Communications and Networking Conference*. | DOI: https://doi.org/10.1109/wcnc61545.2025.10978342 URL: https://jorge.querol.org/publication/resource-allocation-under-uncertainty-in-leo-satel-2025/ - *Abstract*: Low Earth Orbit (LEO) satellite constellations consist of numerous satellites orbiting at different altitudes to serve diverse terrestrial users. Efficient resource management in such dynamic and large-scale networks presents a significant challenge. This paper studies Resource Blocks (RBs) and transmit power allocation at each LEO satellite, aiming at enhancing network performance while meeting Quality of Service (QoS) requirements. A stochastic optimization problem is formulated where the required QoS by each user is expressed as a chance constraint of the minimum data rate requirements considering network dynamics and uncertainties in channel conditions and traffic demands. The Conditional Value at Risk (CVaR) is employed to reformulate the chance constraint into a convex form and achieve a robust solution. Then, an alternating optimization approach is applied to solve the optimization problem. Through simulations using real data from the Starlink constellation, we demonstrate the efficacy of the proposed approach in improving network data rates while maintaining the required QoS levels. 34. **Secrecy Rate Maximization for 6G Reconfigurable Holographic Surfaces Assisted Systems** (2025) — Chandan Kumar Sheemar, Wali Ullah Khan, Marco Di Renzo, Asad Mahmood, Jorge Querol, Symeon Chatzinotas. In *arXiv (Cornell University)*. | DOI: https://doi.org/10.48550/arxiv.2503.01741 URL: https://jorge.querol.org/publication/secrecy-rate-maximization-for-6g-reconfigurable-ho-2025/ - *Abstract*: Reconfigurable holographic surfaces (RHS) have emerged as a transformative material technology, enabling dynamic control of electromagnetic waves to generate versatile holographic beam patterns. This paper addresses the problem of secrecy rate maximization for an RHS-assisted systems by joint designing the digital beamforming, artificial noise (AN), and the analog holographic beamforming. However, such a problem results to be non-convex and challenging. Therefore, to solve it, a novel alternating optimization algorithm based on the majorization-maximization (MM) framework for RHS-assisted systems is proposed, which rely on surrogate functions to facilitate efficient and reliable optimization. In the proposed approach, digital beamforming design ensures directed signal power toward the legitimate user while minimizing leakage to the unintended receiver. The AN generation method projects noise into the null space of the legitimate user channel, aligning it with the unintended receiver channel to degrade its signal quality. Finally, the holographic beamforming weights are optimized to refine the wavefronts for enhanced secrecy rate performance Simulation results validate the effectiveness of the proposed framework, demonstrating significant improvements in secrecy rate compared to the benchmark method. 35. **Enhanced demodulator for 5G NTN using spatio-temporal attention convolutional autoencoder and Akida Brainchip SNN** (2025) — Swetha Varadarajulu, Marcele O. K. Mendonça, Geoffrey Eappen, Jorge Querol, Symeon Chatzinotas. In *IET conference proceedings.*. | DOI: https://doi.org/10.1049/icp.2024.4619 | Open Access: https://orbilu.uni.lu/handle/10993/63270 URL: https://jorge.querol.org/publication/enhanced-demodulator-for-5g-ntn-using-spatio-tempo-2025/ - *Abstract*: This paper presents a novel approach to overcoming challenges in 5G and 6G mobile satellite systems (MSS) in Low Earth Orbit (LEO), focusing on Non-Line-of-Sight (NLOS) issues in 5G Non-Terrestrial Networks (NTN) that connect directly with handheld devices. We utilize a Convolutional Neural Network (CNN) with a Spatio-Temporal Attention Network (STAN) autoencoder, which is then converted into a Spiking Neural Network (SNN) using Brainchip Akida’s Meta TF Software Framework. This integration of neuromorphic processing aims to enhance energy efficiency, reduce computational demands, and increase data transmission rates, optimizing Channel State Information (CSI) in compliance with 3GPP standards. Our STAN-CNN-SNN architecture achieves a 85% reduction in computational requirements, leading to decrease in power consumption, and increase in data rates within the C-Band spectrum. Simulations with LEO satellite MSS parameters demonstrate significant advancements in communication systems. The numerical results demonstrates substantial computational reductions with minimal capacity trade-offs. 36. **Joint Communications and Sensing for 6G Satellite Networks: Use Cases and Challenges** (2025) — Chandan Kumar Sheemar, Prabhu Thiruvasagam, Wali Ullah Khan, Sourabh Solanki, George C. Alexandropoulos, Jorge Querol, Plachy, Jan, Oliver Holschke, Symeon Chatzinotas. In *arXiv (Cornell University)*. | DOI: https://doi.org/10.48550/arxiv.2501.05243 URL: https://jorge.querol.org/publication/joint-communications-and-sensing-for-6g-satellite-2025/ - *Abstract*: Satellite networks (SN) have long provided two fundamental services: global communications and Earth-oriented sensing, supporting applications from connectivity and navigation to disaster management and environmental monitoring. Yet, the accelerating demand for data and the emergence of new applications render the independent evolution of communication and sensing payloads increasingly unsustainable. Joint communications and sensing (JCAS) has emerged as a transformative paradigm, integrating both functions within a unified payload to enhance spectral efficiency, reduce operational costs, and minimize hardware redundancy. Beyond efficiency, this integration creates opportunities for novel services that are infeasible under separate payload designs. This paper motivates the role of JCAS in shaping the sixth-generation (6G) of satellite networks, explores a representative use case to assess its feasibility, and discusses key challenges that must be addressed to unlock its full potential. By highlighting these opportunities inherent to the space environment, we aim to stimulate the development of JCAS as a cornerstone technology for the next-generation space era 37. **User Equivalent Range Error and Positioning Accuracy Analysis for ToA-Based Techniques Using PRS and SSB in 5G/6G NTN** (2025) — Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2025.3623669 | Open Access: https://hdl.handle.net/10993/66129 URL: https://jorge.querol.org/publication/user-equivalent-range-error-and-positioning-accura-2025/ - *Abstract*: The integration of Non-Terrestrial Network (NTN) within the Fifth Generation (5G) and Sixth Generation (6G) ecosystem offers new opportunities for global Positioning, Navigation, and Timing (PNT) services, particularly in environments where Global Navigation Satellite System (GNSS) signals are obstructed or degraded. This work investigates the positioning performance of Time of Arrival (ToA)-based techniques using both Positioning Reference Signal (PRS) and Synchronization Signal Block (SSB) signals in 5G NTN scenarios. A comprehensive User Equivalent Range Error (UERE) model is developed, incorporating satellite, receiver, and propagation-related error sources across FR1 and FR2 frequency bands. The influence of satellite geometry is assessed through a Geometrical Dilution of Precision (GDOP) analysis, while a minimum satellite visibility evaluation quantifies the likelihood of observing at least four satellites above various elevation masks for representative LEO constellations at 600 km and 1200 km altitudes. Monte Carlo simulations quantify the impact of UERE on positioning accuracy, revealing that the 95th-percentile horizontal errors range from approximately 8 m to 26 m, depending on signal type, frequency band, and orbital altitude. The results demonstrate that ToA-based positioning using PRS can surpass typical urban GNSS-level accuracy, highlighting its potential in GNSS-challenged environments. In comparison, SSB-based positioning remains a viable alternative, offering reduced complexity at the cost of moderate accuracy trade-offs. The study offers a unified framework for understanding positioning accuracy in 5G/6G NTN, bridging UERE modeling, satellite visibility, and signal design considerations, and supporting the ongoing development of reliable global PNT services. 38. **Reduced Complexity Initial Synchronization for 5G NR Multibeam LEO-Based Non-Terrestrial Networks** (2025) — Ashish Kumar Meshram, Sumit Kumar, Jorge Querol, Stefano Andrenacci, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2025.3543625 | Open Access: https://hdl.handle.net/10993/64438 URL: https://jorge.querol.org/publication/reduced-complexity-initial-synchronization-for-5g--2025/ - *Abstract*: This paper presents a computationally efficient technique to mitigate the overall Carrier Frequency Offset (CFO) impairment introduced by the User Equipment (UE) crystal oscillator imperfection and the Doppler effect introduced by the satellite and UE movement. We assume steerable multibeam regenerative Low Earth Orbit (LEO) satellite-based 5G New Radio (NR) Non-Terrestrial Networks (NTN) under trajectory uncertainty and beam-pointing errors. The UE and the satellite do not require any prior information on the satellite ephemeris or UE location to achieve initial synchronization. The novelty of our method lies in exploiting the instantaneous satellite state vector for Doppler Pre-Compensation (DPC) to each beam of the LEO satellite relative to its Beam Center (BC). The UE then performs post-compensation to address the residual frequency offset by employing aggregated 5G New Radio (NR) Primary Synchronization Signal (PSS), followed by PSS detection, offering two-fold search space reduction during initial synchronization. We provide practical design parameters for the proposed algorithm to ensure that UE can efficiently perform initial synchronization by evaluating approximate bounds on the spot beam radius along with the No-Benefit Region (NBR) bounds of DPC. We conducted extensive simulations to assess the performance of the S- and Ka-bands under the NTN channel model and validated it with the corresponding analytical expressions conditioned on satellite trajectory uncertainty and beam-pointing error. Our method ensures that the probability of PSS detection remains above 90% while maintaining a false alarm rate of 1% at a Signal-to-Noise Ratio (SNR) as low as −6 (dB) if the standard deviation of the satellite trajectory and beam-pointing errors are within 5 (km) and 0.05°, respectively. 39. **Parallel and Distributed Hybrid Beamforming for Multicell Millimeter Wave MIMO Full Duplex** (2025) — Chandan Kumar Sheemar, Symeon Chatzinotas, Dirk Slock, Eva Lagunas, Jorge Querol. In *IEEE Transactions on Vehicular Technology*. | DOI: https://doi.org/10.1109/TVT.2024.3488956 | Open Access: https://hdl.handle.net/10993/62460 URL: https://jorge.querol.org/publication/parallel-and-distributed-hybrid-beamforming-for-mu-2025/ - *Abstract*: Full duplex (FD) is an auspicious wireless technology that holds the potential to double data rates through simultaneous transmission and reception. This paper proposes two innovative designs of hybrid beamforming (HYBF) for a multicell massive multiple-input-multiple-output (mMIMO) millimeter wave (mmWave) FD system. Initially, we introduce a novel centralized HYBF (C-HYBF) scheme, which employs the minorization-maximization (MM) method. However, while centralized beamforming designs offer superior performance, they suffer from high computational complexity, substantial communication overhead, and demand expensive computational resources. To surmount these challenges, we present a framework that facilitates per-link parallel and distributed HYBF (P$\&$D-HYBF) in the mmWave frequency band. This cooperative approach enables each base station (BS) to independently solve its local, low-complexity sub-problems in parallel, resulting in a substantial reduction in communication overhead and computational complexity. Simulation results demonstrate that P$\&$D-HYBF achieves comparable performance to C-HYBF, and with only a few radio-frequency (RF) chains, both designs surpass the capabilities of fully digital half duplex (HD) systems. 40. **Optimal Linear Precoding Under Realistic Satellite Communications Scenarios** (2025) — Geoffrey Eappen, Jorge Luis González Ríos, Vibhum Singh, Rakesh Palisetty, Alireza Haqiqtnejad, Liz Martínez Marrero, Jevgenij Krivochiza, Jorge Querol, Nicola Maturo, Juan Carlos Merlano Duncán, Eva Lagunas, Stefano Andrenacci, Symeon Chatzinotas. In *IEEE Open Journal of Vehicular Technology*. | DOI: https://doi.org/10.1109/OJVT.2024.3509646 | Open Access: https://hdl.handle.net/10993/63208 URL: https://jorge.querol.org/publication/optimal-linear-precoding-under-realistic-satellite-2025/ - *Abstract*: In this paper, optimal linear precoding for the multibeam geostationary earth orbit (GEO) satellite with the multi-user (MU) multiple-input-multiple-output (MIMO) downlink scenario is addressed. Multiple-user interference is one of the major issues faced by the satellites serving the multiple users operating at the common time-frequency resource block in the downlink channel. To mitigate this issue, the optimal linear precoders are implemented at the gateways (GWs). The precoding computation is performed by utilizing the channel state information obtained at user terminals (UTs). The optimal linear precoders are derived considering beamformer update and power control with an iterative per-antenna power optimization algorithm with a limited required number of iterations. The efficacy of the proposed algorithm is validated using the In-Lab experiment for 16 × 16 precoding with multi-beam satellite for transmitting and receiving the precoded data with digital video broadcasting satellite-second generation extension (DVB-S2X) standard for the GW and the UTs. The software defined radio platforms are employed for emulating the GWs, UTs, and satellite links. The validation is supported by comparing the proposed optimal linear precoder with full frequency reuse (FFR), and minimum mean square error (MMSE) schemes. The experimental results demonstrate that with the optimal linear precoders it is possible to successfully cancel the inter-user interference in the simulated satellite FFR link. Thus, optimal linear precoding brings gains in terms of enhanced signal-to-noise-and-interference ratio, and increased system throughput and spectral efficiency. 41. **Joint Holographic Beamforming and User Scheduling With Individual QoS Constraints** (2025) — Chandan Kumar Sheemar, Christo Kurisummoottil Thomas, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas, Walid Saad. In *IEEE Transactions on Vehicular Technology*. | DOI: https://doi.org/10.1109/TVT.2025.3569401 URL: https://jorge.querol.org/publication/joint-holographic-beamforming-and-user-scheduling--2025/ - *Abstract*: Reconfigurable holographic surfaces (RHS) have emerged as a transformative material technology, enabling dynamic control of electromagnetic waves to generate versatile holographic beam patterns. This paper addresses the problem of joint hybrid holographic beamforming and user scheduling under per-user minimum quality-of-service (QoS) constraints, a critical challenge in resource-constrained networks. However, such a problem results in mixed- integer non-convex optimization, making it difficult to identify feasible solutions efficiently. To overcome this challenge, we propose a novel iterative optimization framework that jointly solves the problem to maximize the RHS-assisted network sum-rate, efficiently managing holographic beamforming patterns, dynamically scheduling users, and ensuring the minimum QoS requirements for each scheduled user. The proposed framework relies on zero-forcing digital beamforming, gradient-ascent-based holographic beamformer optimization, and a greedy user selection principle. Our extensive simulation results validate the effectiveness of the proposed scheme, demonstrating their superior performance compared to the benchmark algorithms in terms of sum-rate performance, while meeting the minimum per-user QoS constraints. 42. **Joint Communication and Positioning Receiver Architecture for DSSS-Overlayed OFDM Waveform** (2025) — Alejandro Gonzalez-Garrido, Idir Edjekouane, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2025.3615957 | Open Access: https://hdl.handle.net/10993/65924 URL: https://jorge.querol.org/publication/joint-communication-and-positioning-receiver-archi-2025/ - *Abstract*: The integration of satellite systems within the 5G new radio (NR) framework, designated as non-terrestrial networks (NTNs), relies on global navigation satellite systems (GNSS) to achieve precise synchronization. However, dependence on GNSS presents significant vulnerabilities in scenarios involving signal degradation, jamming, or spoofing, alongside increased cost and power consumption issues, particularly in extensive internet of things (IoT) deployments. To address these challenges, this paper proposes an innovative joint communication and positioning (JCAP) receiver architecture, which integrates direct sequence spread spectrum (DSSS) signals into the 5G orthogonal frequency division multiplexing (OFDM) waveform, enabling GNSS-free synchronization and positioning capabilities without embedded pilot overhead. The proposed hybrid architecture jointly exploits DSSS for robust channel parameter estimation and OFDM for high-throughput communication, thereby reducing the pilots signals traditionally required for synchronization and channel estimation. Comprehensive evaluations demonstrate that the proposed JCAP receiver achieves reliable detection and accurate estimation of delay and Doppler parameters, maintaining low bit error rates (BER) under realistic signal-to-interference ratios (SIR). The findings underscore the feasibility and effectiveness of the proposed hybrid scheme, paving the way for resilient GNSS-free operations in 5G NTN environments. 43. **Joint Communication and Navigation From LEO Multi-Beam Satellite** (2025) — Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2025.3568093 | Open Access: https://hdl.handle.net/10993/65616 URL: https://jorge.querol.org/publication/joint-communication-and-navigation-from-leo-multi--2025/ - *Abstract*: This paper investigates an innovative approach to enable Joint Communication and Positioning (JCAP) in 5G Non-Terrestrial Networks (NTN) using Low Earth Orbit (LEO) multi-beam satellite systems. The integration of communication and navigation services is achieved by aggregating a Direct-Sequence Spread Spectrum (DSSS) as a navigation signal with a 5G Orthogonal Frequency-Division Multiplexing (OFDM) waveform for communication services. Two models are proposed for resource allocation and signal aggregation, referred to as the shared beam model, where communication and navigation signals are aggregated prior to Digital Beamforming (DBF) within the same beam; and the independent beam model, which employs separate beams for communication and navigation, with the navigation beam designed to be significantly wider than the communication beams, resulting in overlap between the two. The performance of these models is assessed using as Key Performance Indicators (KPI) the Cramer-Rao Lower Bound (CRLB) for range estimation used in navigation and the spectral efficiency for the broadband service. The study formulates and addresses a multi-objective optimization problem to derive the Pareto front, highlighting the trade-off between communication and navigation performance. Extensive simulations demonstrate the efficacy of the proposed models in terms of spectral efficiency and accuracy in range estimation, and results have been compared with those obtained from the current 5G positioning system. The models have been evaluated in two distinct scenarios: one without frequency reuse between beams and another incorporating a three-color frequency reuse scheme. The results indicate that the independent beams model outperforms the shared beams model by reducing inter-beam interference in both scenarios. The proposed solution maintains backward compatibility with existing 5G NTN, facilitating uninterrupted positioning and communication services in GNSS-denied environments. Furthermore, the combination of DSSS and OFDM enhances the reliability of the data service by utilizing the DSSS sequence as a digital signature for the waveform. This work establishes a foundation for robust and efficient JCAP implementations, addressing challenges related to multi-beam interference and resource optimization. 44. **A Vision, Survey, and Roadmap Toward Space Communications in the 6G and Beyond Era** (2025) — Konstantinos Ntontin, Eva Lagunas, Jorge Querol, Junaid ur Rehman, Joël Grotz, Symeon Chatzinotas, Björn Ottersten. In *Proceedings of the IEEE*. | DOI: https://doi.org/10.1109/JPROC.2024.3512934 | Open Access: https://hdl.handle.net/10993/63599 URL: https://jorge.querol.org/publication/a-vision-survey-and-roadmap-toward-space-communica-2025/ - *Abstract*: Satellite communications (SatComs) have recently been through a renaissance, both technologically and entrepreneurially. Ambitious plans have already come into fruition with the operation of low-Earth orbit (LEO) constellations including thousands of satellites and supported by state of the art but proprietary technologies, such as active antenna arrays and intersatellite links (ISLs). In this context, this article aims to provide a forward-looking vision of use cases and a deep dive into technological enablers that will be prominent in space communications beyond 2030. In parallel, it motivates how open standards can play a role in delivering affordable communication services in space. Starting from the 5G plans for nonterrestrial networks, we provide a survey and roadmap toward artificial intelligence (AI)-supported satellite systems, space-enabled quantum networks, and joint communications and positioning (JCAP) for space missions and interplanetary exploration. 45. **5G-NR Over Transparent Payload GEO Satellites: A Hands-On Approach Using OpenAirInterface5G-NTN** (2025) — Sumit Kumar, Jevgenij Krivochiza, Türker Yilmaz, Jorge Querol, Symeon Chatzinotas, Stefano Andrenacci, Joël Grotz. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2025.3586871 | Open Access: https://hdl.handle.net/10993/65428 URL: https://jorge.querol.org/publication/5g-nr-over-transparent-payload-geo-satellites-a-ha-2025/ - *Abstract*: The inclusion of Non-Terrestrial Network (NTN) components has significantly enhanced the reach of 5G networks. OpenAirInterface5G (OAI) has developed an open-source, Software-Defined Radio (SDR)-based framework for 5G-NTN, using its Terrestrial Network (TN) protocol stack as the baseline. OAI’s 5G-NTN adaptations are still evolving, requiring in-lab validations and field trials to assess its effectiveness in addressing the unique challenges of NTN components and channel characteristics. Live satellite tests, unlike simulations, demand manual tuning of key parameters like carrier frequency offset, timing offsets, and gain calibration. In this work, we present a practical approach for deploying 5G over GEO satellites using the OAI 5G-NTN suite, addressing (a) satellite channel impairments and (b) limitations in OAI’s current 5G-NTN implementation. Our work provides step-by-step calibrations, ensuring both experiment reproducibility and the realization of a full 5G-NTN link. We further identify the performance bottlenecks and experiment with (a) Radio Link Control Acknowledgment Mode (RLC-AM) parameters and (b) Low-Density Parity Check (LDPC) iterations to improve end-to-end throughput. We validate our methods via live tests over a transparent payload GEO satellite. We believe that our work represents a critical step in bridging the gap between lab-based 5G-NTN emulation and live satellite testing, offering valuable insights to advance 5G-NTN research and development. 46. **Resource-Efficient FPGA Architecture for Real-Time RFI Mitigation in Interferometric Radiometers** (2024) — Adrián Pérez-Portero, Jorge Querol, Adriano Camps. In *Sensors*. | DOI: https://doi.org/10.3390/s24248001 | Open Access: https://hdl.handle.net/10993/67072 URL: https://jorge.querol.org/publication/resource-efficient-fpga-architecture-for-real-time-2024/ - *Abstract*: Interferometric radiometers operating at L-band, such as ESA's SMOS mission, enable crucial Earth observations providing high-resolution measurements of soil moisture, ocean salinity, and other geophysical parameters. However, the increasing electromagnetic spectrum utilization has led to significant Radio Frequency Interference (RFI) challenges, particularly critical given the sensors' fine temperature resolution requirements of less than 1 K. This work presents the hardware implementation of an advanced RFI detection and mitigation algorithm specifically designed for interferometric radiometers, targeting future L-band missions. The implementation processes 1-bit quantized signals at 57.69375 MHz from multiple receivers, employing time-frequency analysis and polarimetric detection techniques while optimizing Field Programmable Gate Array (FPGA) resource utilization. Novel optimization strategies include overclocked processing cores operating at 230.775 MHz, efficient resource sharing through operation serialization, and strategic memory management. The system achieves real-time processing capabilities while maintaining detection probabilities above 63% with false alarm rates below 1% for typical interference scenarios. Performance validation using synthetic datasets demonstrates robust operation across various RFI conditions, making this implementation suitable as part of the RFI detection and mitigation efforts for future interferometric radiometer missions beyond SMOS. 47. **Development of a Dynamically Re-Configurable Radio-Frequency Interference Detection System for L-Band Microwave Radiometers** (2024) — Adrián Pérez-Portero, Jorge Querol, Andreu Mas-Viñolas, A. Amézaga, R. Jove‐Casulleras, Adriano Camps. In *Sensors*. | DOI: https://doi.org/10.3390/s24134034 | Open Access: https://hdl.handle.net/10993/62571 URL: https://jorge.querol.org/publication/development-of-a-dynamically-re-configurable-radio-2024/ - *Abstract*: Real-Time RFI Detection and Flagging (RT-RDF) for microwave radiometers is a versatile new FPGA algorithm designed to detect and flag Radio-Frequency Interference (RFI) in microwave radiometers. This block utilizes computationally-efficient techniques to identify and analyze RF signals, allowing the system to take appropriate measures to mitigate interference and maintain reliable performance. With L-Band microwave radiometry as the main application, this RFI detection algorithm focuses on the Kurtogram and Spectrogram to detect non-Gaussian behavior. To gain further modularity, an FFT-based filter bank is used to divide the receiver's bandwidth into several sub-bands within the band of interest of the instrument, depending on the application. Multiple blanking strategies can then be applied in each band using the provided detection flags. The algorithm can be re-configured in the field, for example with dynamic integration times to support operation in different environments, or configurable thresholds to account for variable RFI environments. A validation and testing campaign has been performed on multiple scenarios with the ARIEL commercial microwave radiometer, and the results confirm the excellent performance of the system. 48. **Towards 6G-UAV Disaster-Resilient Networks** (2024) — Youssouf DRIF, Abhishek BERA, Jorge Querol, Miguel Angel OLIVARES MENDEZ, Symeon CHATZINOTAS. In *IEEE International Symposium on Personal, Indoor and Mobile Radio Communications*. | Open Access: https://hdl.handle.net/10993/62635 URL: https://jorge.querol.org/publication/drif-2024-towards/ - *Abstract*: During natural disasters such as earthquakes, wildfires, hurricanes, landslides, tsunamis, CBRNE (chemical, medical, radiological, nuclear, or explosive) incidents, or terrorist threats, critical infrastructure can be severely damaged, with rescue workers facing immense obstacles. Providing help and reaching affected areas can be hazardous for human rescue personnel. To overcome this issue, 5G-enabled UAVs can play a significant role in deploying disaster-resilient networks. Such networks imply multiple challenges, including end-to-end communication reliability and low latency for UAV real-time control. In this paper, we focus on the end-to-end communication aspects of such networks. We present and implement our disaster-resilient network based on a combination of 5G-UAVs and satellite networks. We highlight the related challenges and define solutions based on 5G, Multi-access Edge Computing, UAVs, and dynamic geofencing. We integrate these solutions in an end-to-end network architecture and ultimately deploy it on a national joint 5G-satellite infrastructure to assess its performance. It performs well and demonstrates a recovery time of less than 30 seconds with $\mathbf{9 9 \%}$ network availability. 49. **Supervised Learning Based Real-Time Adaptive Beamforming On-Board Multibeam Satellites** (2024) — Flor Ortiz, Juan A Vasquez-Peralvo, Jorge Querol, Eva Lagunas, Jorge L González Rios, Marcele OK Mendonça, Luis Garces, Victor Monzon Baeza, Symeon Chatzinotas. In *2024 18th European Conference on Antennas and Propagation (EuCAP)*. | Open Access: https://hdl.handle.net/10993/64296 URL: https://jorge.querol.org/publication/ortiz-2024-supervised/ - *Abstract*: Satellite communications (SatCom) are crucial for global connectivity, especially in the era of emerging technologies like 6G and narrowing the digital divide. Traditional SatCom systems struggle with efficient resource management due to static multibeam configurations, hindering quality of service (QoS) amidst dynamic traffic demands. This paper introduces an innovative solution - real-time adaptive beamforming on multibeam satellites with software-defined payloads in geostationary orbit (GEO). Utilizing a Direct Radiating Array (DRA) with circular polarization in the 17.7 - 20.2 GHz band, the paper outlines DRA design and a supervised learning-based algorithm for on-board beamforming. This adaptive approach not only meets precise beam projection needs but also dynamically adjusts beamwidth, minimizes sidelobe levels (SLL), and optimizes effective isotropic radiated power (EIRP). 50. **Rate-Splitting Multiple Access for Secure Communications Over CR MISO SWIPT Systems With Non-Linear EH Users** (2024) — Carla E. García, Mario R. Camana, Jorge Querol, Symeon Chatzinotas. In *IEEE Transactions on Green Communications and Networking*. | DOI: https://doi.org/10.1109/TGCN.2024.3404891 | Open Access: https://hdl.handle.net/10993/62419 URL: https://jorge.querol.org/publication/rate-splitting-multiple-access-for-secure-communic-2024/ - *Abstract*: In this paper, we investigate a secure transmission for a rate-splitting multiple-access (RSMA)-based multiple-input single-output (MISO) underlay cognitive radio (CR) system. The proposed network is composed of a set of secondary users (SUs) that utilize simultaneous wireless information and power transfer (SWIPT) technology and an additional set of non-linear energy harvesting (EH) users. Moreover, the system model under consideration is exposed to multiple eavesdroppers. Thus, we propose to minimize the transmit power intended to the SUs and EH users while maximizing the artificial noise (AN) generated by the secondary transmitter, aiming to counter eavesdroppers’ wiretaps while satisfying the quality-of-service constraints. Therefore, we develop a novel approach based on ant colony regression (ACOR) and semidefinite relaxation (SDR) methods to solve the challenging and non-convex problem which is further transformed into a bilevel optimization problem. Afterward, we investigate a comparative solution based on the particle swarm optimization (PSO) algorithm, the successive convex approximation (SCA) technique, and analyze the incidence of linear and non-linear EH designs. In addition, we compare the RSMA-based scheme with non-orthogonal multiple-access (NOMA), space-division multiple access (SDMA), and zero-forcing (ZF) techniques. Satisfactorily, simulation results prove the proposed ACOR-SDR framework achieves better performance and lower complexity than its counterparts. 51. **Performance Evaluation of Neuromorphic Hardware for Onboard Satellite Communication Applications** (2024) — Eva Lagunas, Flor Ortiz, Geoffrey Eappen, Saed Daoud, Wallace Alves Martins, Jorge Querol, Symeon Chatzinotas, Nicolas Skatchkovsky, Bipin Rajendran, Osvaldo Simeone. In *arXiv preprint arXiv:2401.06911*. | Open Access: https://hdl.handle.net/10993/62418 URL: https://jorge.querol.org/publication/lagunas-2024-performance/ - *Abstract*: Spiking neural networks (SNNs) implemented on neuromorphic processors (NPs) can enhance the energy efficiency of deployments of artificial intelligence (AI) for specific workloads. As such, NPs represent an interesting opportunity for implementing AI tasks power-limited onboard satellite communication spacecraft. In this article, we disseminate the findings of a recently completed study which targeted the comparison, in terms of performance and power-consumption, of different satellite communication use cases implemented on standard AI accelerators and on NPs. In particular, the article describes three prominent use cases, namely payload resource optimization, onboard interference detection and classification, and dynamic receive beamforming; and compares the performance of conventional convolutional neural networks (CNNs) implemented on Xilinx's VCK5000 Versal development card, and SNNs on Intel's neuromorphic chip Loihi 2. 52. **Optimal Linear Precoding Under Realistic Satellite Communications Scenarios** (2024) — Geoffrey Eappen, Jorge Luis Gonzalez, Vibhum Singh, Rakesh Palisetty, Alireza Haqiqtnejad, Liz Martinez Marrero, Jevgenij Krivochiza, Jorge Querol, Nicola Maturo, Juan Carlos Merlano Duncan, Eva Lagunas, Stefano Andrenacci, Symeon Chatzinotas. In *arXiv preprint arXiv:2408.08621*. | Open Access: https://hdl.handle.net/10993/63208 URL: https://jorge.querol.org/publication/eappen-2024-optimal/ - *Abstract*: In this paper, optimal linear precoding for the multibeam geostationary earth orbit (GEO) satellite with the multi-user (MU) multiple-input-multiple-output (MIMO) downlink scenario is addressed. Multiple-user interference is one of the major issues faced by the satellites serving the multiple users operating at the common time-frequency resource block in the downlink channel. To mitigate this issue, the optimal linear precoders are implemented at the gateways (GWs). The precoding computation is performed by utilizing the channel state information obtained at user terminals (UTs). The optimal linear precoders are derived considering beamformer update and power control with an iterative per-antenna power optimization algorithm with a limited required number of iterations. The efficacy of the proposed algorithm is validated using the In-Lab experiment for 16 × 16 precoding with multi-beam satellite for transmitting and receiving the precoded data with digital video broadcasting satellite-second generation extension (DVB-S2X) standard for the GW and the UTs. The software defined radio platforms are employed for emulating the GWs, UTs, and satellite links. The validation is supported by comparing the proposed optimal linear precoder with full frequency reuse (FFR), and minimum mean square error (MMSE) schemes. The experimental results demonstrate that with the optimal linear precoders it is possible to successfully cancel the inter-user interference in the simulated satellite FFR link. Thus, optimal linear precoding brings gains in terms of enhanced signal-to-noise-and-interference ratio, and increased system throughput and spectral efficiency. 53. **Multibeam Beamforming for Direct Radiating Arrays in Satellite Communications Using Genetic Algorithm** (2024) — Juan A. Vásquez-Peralvo, Jorge Querol, Flor Ortíz, Jorge Luis González Ríos, Eva Lagunas, Luis Manuel Garcés-Socarrás, Juan Carlos Merlano Duncán, Marcele O. K. Mendonça, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2024.3385021 | Open Access: https://hdl.handle.net/10993/63005 URL: https://jorge.querol.org/publication/multibeam-beamforming-for-direct-radiating-arrays--2024/ - *Abstract*: Recent advancements in onboard satellite communication have enhanced the capability of dynamically modifying the radiation pattern of a Direct Radiating Array (DRA). This is crucial not only for conventional communication satellites like Geostationary Orbit (GEO) but also for those in lower orbits such as Low Earth Orbit (LEO). Key design factors include the number of beams, beamwidth, Effective Isotropic Radiated Power (EIRP), and Side Lobe Level (SLL) for each beam. However, a challenge arises in multibeam scenarios when trying to simultaneously meet requirements for the aforementioned design factors which are reflected as uneven power distribution. This leads to over-saturation, especially in centrally located antenna elements due to the activation times per beam, commonly referred to as activation instances. In response to this challenge, this paper presents a method to balance the activation instances across antenna elements for each required beam. Our focus is on beams operating at 19 GHz on a CubeSat positioned 500 km above the Earth’s surface. We introduce a Genetic Algorithm (GA)-based algorithm to optimize the beamforming coefficients by modulating the amplitude component of the weight matrix for each antenna element. A key constraint of this algorithm is a limit on activation instances per element, which avoids over-saturation in the Radio Frequency (RF) chain. Additionally, the algorithm accommodates beam requirements such as beamwidth, SLL, pointing direction, and total available power. With the previous key design factors, the algorithm will optimize the required genes to address the desired beam characteristics and constraints. We tested the algorithm’s effectiveness in three scenarios using an 8×8 DRA patch antenna with circular polarization, arranged in a triangular lattice. The results demonstrate that our algorithm not only meets the required beam pattern specifications but also ensures a uniform activation distribution across the antenna array. 54. **ML-based PBCH symbol detection and equalization for 5G Non-Terrestrial Networks** (2024) — Inés Larráyoz-Arrigote, Marcele OK Mendonça, Alejandro Gonzalez-Garrido, Jevgenij Krivochiza, Sumit Kumar, Jorge Querol, Joel Grotz, Symeon Chatzinotas. In *2024 IEEE International Mediterranean Conference on Communications*. | Open Access: https://hdl.handle.net/10993/58851 URL: https://jorge.querol.org/publication/larrayoz-2024-ml/ - *Abstract*: This paper delves into the application of Machine Learning (ML) techniques in the realm of 5G Non-Terrestrial Networks (5G-NTN), particularly focusing on symbol detection and equalization for the Physical Broadcast Channel (PBCH). As 5G-NTN gains prominence within the 3GPP ecosystem, ML offers significant potential to enhance wireless communication performance. To investigate these possibilities, we present ML-based models trained with both synthetic and real data from a real 5G over-the-satellite testbed. Our analysis includes examining the performance of these models under various Signal-to-Noise Ratio (SNR) scenarios and evaluating their effectiveness in symbol enhancement and channel equalization tasks. The results highlight the ML performance in controlled settings and their adaptability to real-world challenges, shedding light on the potential benefits of the application of ML in 5G-NTN. 55. **Interference analysis of Positioning Reference Signals in 5G NTN** (2024) — Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas. In *arXiv preprint arXiv:2401.09157*. | DOI: https://doi.org/10.48550/arxiv.2401.09157 URL: https://jorge.querol.org/publication/gonzalez-2024-interference/ - *Abstract*: Accurate asset localization holds paramount importance across various industries, ranging from transportation management to search and rescue operations. In scenarios where traditional positioning equations cannot be adequately solved due to limited measurements obtained by the receiver, the utilization of Non-Terrestrial Networks (NTN) based on Low Earth Orbit (LEO) satellites can prove pivotal for precise positioning. The decision to employ NTN in lieu of conventional Global Navigation Satellite Systems (GNSS) is rooted in two key factors. Firstly, GNSS systems are susceptible to jamming and spoofing attacks, thereby compromising their reliability, where LEO satellites link budgets can benefit from a closer distances and the new mega constellations could offer more satellites in view than GNSS. Secondly, 5G service providers seek to reduce dependence on third-party services. Presently, the NTN operation necessitates a GNSS receiver within the User Equipment (UE), placing the service provider at the mercy of GNSS reliability. Consequently, when GNSS signals are unavailable in certain regions, NTN services are also rendered inaccessible. 56. **Interference Analysis and Modeling of Positioning Reference Signals in 5G NTN** (2024) — Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2024.3503692 | Open Access: https://hdl.handle.net/10993/62655 URL: https://jorge.querol.org/publication/interference-analysis-and-modeling-of-positioning--2024/ - *Abstract*: The integration of Positioning, Navigation, and Timing (PNT) services within the 5G non-terrestrial networks (NTN) infrastructure is necessary to eliminate the need for a GNSS receiver in the user terminal. Using the positioning reference signal (PRS) in an NTN scenario presents significant challenges, such as interference analysis from the transmission of multiple PRS signals. This study provides a stochastic model for the interference generated by PRS transmissions in a 5G NTN scenario. This model has been derived empirically from a Monte Carlo simulator designed specifically for this purpose, showing that the distribution that best fits the interference is a Generalized Extreme Value (GEV) distribution. The parameters of this distribution are also modeled based on the PRS configuration. Therefore, a designer can use this model to evaluate the probability of encountering certain levels of interference. 57. **Holographic MIMO for Next Generation Non-Terrestrial Networks: Motivation, Opportunities, and Challenges** (2024) — Giovanni Iacovelli, Chandan Kumar Sheemar, Wali Ullah Khan, Asad Mahmood, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas. In *arXiv preprint arXiv:2411.10014*. | DOI: https://doi.org/10.48550/arXiv.2411.10014 URL: https://jorge.querol.org/publication/iacovelli-2024-holographic/ - *Abstract*: In this article, we propose the integration of the holographic multiple-input multiple-output (HMIMO) as a transformative solution for next-generation nonterrestrial networks (NTNs), addressing key challenges, such as high hardware costs, launch expenses, and energy inefficiency. Traditional NTNs are constrained by the financial and operational limitations posed by bulky and costly antenna systems, alongside the complexities of maintaining effective communications in space. HMIMO offers a novel approach utilizing compact and lightweight arrays of densely packed radiating elements with real-time reconfiguration capabilities, thus capable of optimizing system performance under dynamic conditions such as varying orbital dynamics and Doppler shifts. By replacing conventional antenna systems with HMIMO, the number of required radio-frequency (RF) chains can be cut to roughly one-tenth while achieving about threefold lower power consumption and an order-of-magnitude decrease in hardware cost. Thus, manufacturing and launch expenses can be substantially reduced, paving the way for more streamlined and cost-effective NTN deployments. This advancement holds significant potential to democratize space communications, making them accessible to a broader range of stakeholders, including smaller nations and commercial enterprises. Moreover, the inherent capabilities of HMIMO in enhancing energy efficiency, scalability, and adaptability position this technology as a key enabler of new use cases and sustainable satellite operations. 58. **High-Resolution 5G Active Antenna Beam Pattern Measurement Using UAVs** (2024) — DMKK Venkateswara Rao, Sumit Kumar, Hamed Habibi, Jorge Querol, Symeon Chatzinotas, Holger Voos. In *2024 International Conference on Unmanned Aircraft Systems (ICUAS)*. | Open Access: https://hdl.handle.net/10993/63519 URL: https://jorge.querol.org/publication/rao-2024-high/ - *Abstract*: This paper presents a measurement methodology for obtaining a high-resolution beam pattern of 5G active antenna systems (AASs) using Unmanned Aerial Vehicles (UAVs). Beam pattern measurements are typically conducted in an anechoic chamber by placing the active antenna at the center and radiation pattern is measured at various angles. This approach is limited by the spatial constraints of the chamber and is time-consuming for obtaining high-resolution measurements. To address this problem, UAVs equipped with measurement sensors are proposed to fly around the antenna and do the measurement campaign. The beam pattern measurement campaign problem is formulated into a UAV path planning problem. Horizontal circular arcs at various elevation angles are defined on a sphere centered at the antenna and connected at their ends alternatively to define a reference path and transcribe it into a reference trajectory for the UAV. A chattering-free super-twisting controller is designed to accurately track this trajectory against unknown matched disturbances and model uncertainties. The proposed methodology is validated by an indoor experiment with a horn antenna set up to operate in the frequency range of a 5G AAS and create a stationary beam. A universal software radio peripheral is mounted on a UAV and programmed to measure the received signal strength indicator in real time and a high-resolution beam pattern is satisfactorily captured. 59. **Harnessing Supervised Learning for Adaptive Beamforming in Multibeam Satellite Systems** (2024) — Flor Ortiz, Juan A Vasquez-Peralvo, Jorge Querol, Eva Lagunas, Jorge L González Rios, Luis Garces, Victor Monzon-Baeza, Symeon Chatzinotas. In *2024 IEEE International Conference on Machine Learning for Communication*. | Open Access: https://hdl.handle.net/10993/59939 URL: https://jorge.querol.org/publication/ortiz-2024-harnessing/ - *Abstract*: In today’s ever-connected world, the demand for fast and widespread connectivity is insatiable, making multibeam satellite systems an indispensable pillar of modern telecommunications infrastructure. However, the evolving communication landscape necessitates a high degree of adaptability. This adaptability is particularly crucial for beamforming, as it enables the adjustment of peak throughput and beamwidth to meet fluctuating traffic demands by varying the beamwidth, side lobe level (SLL), and effective isotropic radiated power (EIRP). This paper introduces an innovative approach rooted in supervised learning to efficiently derive the requisite beamforming matrix, aligning it with system requirements. Significantly reducing computation time, this method is uniquely tailored for real-time adaptation, enhancing the agility and responsiveness of satellite multibeam systems. Exploiting the power of supervised learning, this research enables multibeam satellites to respond quickly and intelligently to changing communication needs, ultimately ensuring uninterrupted and optimized connectivity in a dynamic world. 60. **Graph Neural Network Pooling for BCH Channel Decoding in Software Defined Satellites** (2024) — Swetha Varadarajulu, Victor Monzon Baeza, Jorge Querol, Marcele OK Mendonca, Symeon Chatzinotas. In *2024 IEEE International Conference on Communications Workshops (ICC*. | Open Access: https://hdl.handle.net/10993/63269 URL: https://jorge.querol.org/publication/varadarajulu-2024-graph/ - *Abstract*: This paper delves into the transformative impact of Deep Learning (DL) techniques on decoding tasks at the physical layer onboard regenerative software-defined satellites, reshaping traditional error correction methodologies. Specifically, we focus on the integration of Graph Neural Networks (GNNs) for channel decoding, which offers a fresh perspective by adeptly handling graph-structured data and effectively modelling intricate interference and channel dependencies. The study systematically explores the potential performance tradeoffs that arise from modifying the graph structure. Furthermore, we extend our investigation by implementing the message-passing algorithm with GNN, employing a topk pooling method following pick, prune, and link optimization strategies. This strategic approach aims to mitigate computational complexity and minimize latency, by 30 to 35 % which is particularly advantageous for decoding BCH codes. This advancement promises to enhance the efficiency of communication systems sianificantly, 61. **Genetic algorithm-based beamforming in subarray architectures for geo satellites** (2024) — Juan Andrés Vásquez-Peralvo, Jorge Querol, Eva Lagunas, Flor Ortiz, Luis Manuel Garcés-Socarrás, Jorge Luis González-Rios, Victor Monzon Baeza, Symeon Chatzinotas. In *2024 18th European Conference on Antennas and Propagation (EuCAP)*. | Open Access: https://hdl.handle.net/10993/62760 URL: https://jorge.querol.org/publication/vasquez-2024-genetic/ - *Abstract*: The incorporation of subarrays in Direct Radiating Arrays for satellite missions is fundamental in reducing the number of Radio Frequency chains, which correspondingly diminishes cost, power consumption, space, and mass. Despite the advantages, previous beamforming schemes incur significant losses during beam scanning, particularly when hybrid beamforming is not employed. Consequently, this paper introduces an algorithm capable of compensating for these losses by increasing the power, for this, the algorithm will activate radiating elements required to address a specific Effective Isotropic Radiated Power for a beam pattern over Earth, projected from a GeoStationary satellite. In addition to the aforementioned compensation, other beam parameters have been addressed in the algorithm, such as beamwidth and Side Lobe Levels. To achieve these objectives, we propose employing the array thinning concept through the use of genetic algorithms, which enable beam shaping with the desired characteristics and power. The full array design considers an open-ended waveguide, configured to operate in circular polarization within the Ka-band frequency range of 17.7-20.2 GHz. 62. **Flexible Synchronous Federated Learning Approach for LEO Satellite Constellation Networks** (2024) — Madyan Alsenwi, Eva Lagunas, Jorge Querol, Mohammed Al-Ansi, Symeon Chatzinotas. In *2024 IEEE International Mediterranean Conference on Communications*. | Open Access: https://hdl.handle.net/10993/61532 URL: https://jorge.querol.org/publication/alsenwi-2024-flexible/ - *Abstract*: This paper presents a flexible synchronous federated learning (FlexSync-FL) approach for Low Earth Orbit (LEO) satellite constellation networks, where LEO satellites train local models and conduct a collaborative global model at the Network Operations Center (NOC). Unlike the standard synchronous FL, FlexSync-FL employs a dual-trigger synchronization mechanism that initiates global model aggregation either upon receiving updates from all clients (satellites) or after a predefined maximum interval time has elapsed. Furthermore, FlexSync-FL leverages inter-satellite links (ISLs) to facilitate forwarding local models among satellites, especially for those without direct visibility to ground gateway stations (GWs). In particular, FlexSync-FL aims to mitigate the impact of long latency and intermittent connectivity, inherent in satellite networks, on the FL process. The effectiveness of the proposed FlexSync-FL framework is demonstrated through simulations that employ Long ShortTerm Memory (LSTM) networks to train local models at each LEO satellite for traffic forecasting using real-world aeronautical datasets. 63. **Flexible Payload Configuration for Satellites using Machine Learning** (2024) — Marcele OK Mendonça, Flor G Ortiz-Gomez, Jorge Querol, Eva Lagunas, Juan A Vásquez Peralvo, Victor Monzon Baeza, Symeon Chatzinotas, Bjorn Ottersten. In *2024 IEEE International Conference on Machine Learning for Communication*. | Open Access: https://hdl.handle.net/10993/58800 URL: https://jorge.querol.org/publication/mendoncca-2024-flexible/ - *Abstract*: Satellite communications, essential for modern connectivity, extend access to maritime, aeronautical, and remote areas where terrestrial networks are unfeasible. Current GEO systems distribute power and bandwidth uniformly across beams using multi-beam footprints with fractional frequency reuse. However, recent research reveals the limitations of this approach in heterogeneous traffic scenarios, leading to inefficiencies. To address this, this paper presents a machine learning (ML)-based approach to Radio Resource Management (RRM).We treat the RRM task as a regression ML problem, integrating RRM objectives and constraints into the loss function that the ML algorithm aims at minimizing. Moreover, we introduce a context-aware ML metric that evaluates the ML model’s performance but also considers the impact of its resource allocation decisions on the overall performance of the communication system. 64. **Enhancing Handover Performance in LEO Satellite Networks with Multi-Connectivity and Conditional Handover Approach** (2024) — Mohammed Al-Ansi, Jorge Querol, Madyan Alsenwi, Eva Lagunas, Symeon Chatzinotas. In *2024 International Conference on Software, Telecommunications and Computer*. | Open Access: https://hdl.handle.net/10993/62165 URL: https://jorge.querol.org/publication/al-2024-enhancing/ - *Abstract*: Low Earth orbit (LEO) satellites have emerged as an essential technology for 5G and beyond, with the capability to provide high-speed Internet connectivity on a global scale. However, the continuous movement of these satellites is a significant challenge. Most existing handover (HO) solutions rely on switching between serving and target satellites, resulting in a single-connectivity (SC) hard HO. In contrast, this study introduces a soft-HO methodology that uses dual connectivity and packet duplication during the multi-coverage period to connect users to both serving and target satellites via a multiconnectivity (MC) architecture. MC-HO considers the conditional HO technique and location-based trigger criterion. Compared to SC-HO, MC-HO exhibits a reduction in the average number of HOs and radio link failures. Thus, the proposed approach promises to improve the performance of handover, resulting in more stable and reliable connectivity. 65. **Energy-efficient precoding and feeder-link-beam matching design for bent-pipe satcom systems** (2024) — Vu Nguyen Ha, Juan Carlos Merlano Duncan, Eva Lagunas, Jorge Querol, Symeon Chatzinotas. In *ICC 2024-IEEE International Conference on Communications*. | Open Access: https://hdl.handle.net/10993/61310 URL: https://jorge.querol.org/publication/ha-2024-energy/ - *Abstract*: This paper proposes a joint optimization framework for energy-efficient linear precoding and feeder-link-beam matching design in a multi-gateway multi-beam bent-pipe satellite communication system. The proposed scheme jointly optimizes the precoding vectors at the gateway antennas and amplifying-and-matching mechanism at the satellite to maximize the system-weighted energy efficiency under the transmit power budget constraint. The technical designs are formulated into a non-convex sparsity problem consisting of a fractional-form objective function and sparsity-related constraints. To address these challenges, two iterative efficient designs are proposed by utilizing the concepts of Dinkelbach's method and the compressed-sensing approach. The simulation results demonstrate the effectiveness of the proposed scheme compared to another benchmark method. 66. **Energy-Efficient Precoding and Feeder-Link-Beam Matching Design for Bent-Pipe SATCOM Systems** (2024) — Vu Nguyen Ha, Juan Carlos Merlano Duncan, Eva Lagunas, Jorge Querol, Symeon Chatzinotas. In *ArXiv*. | Open Access: https://hdl.handle.net/10993/61310 URL: https://jorge.querol.org/publication/energy-efficient-precoding-and-feeder-link-beam-ma-2024/ - *Abstract*: This paper proposes a joint optimization framework for energy-efficient linear precoding and feeder-link-beam matching design in a multi-gateway multi-beam bent-pipe satellite communication system. The proposed scheme jointly optimizes the precoding vectors at the gateway antennas and amplifying-and-matching mechanism at the satellite to maximize the system-weighted energy efficiency under the transmit power budget constraint. The technical designs are formulated into a non-convex sparsity problem consisting of a fractional-form objective function and sparsity-related constraints. To address these challenges, two iterative efficient designs are proposed by utilizing the concepts of Dinkelbach's method and the compressed-sensing approach. The simulation results demonstrate the effectiveness of the proposed scheme compared to another benchmark method. 67. **Edge Learning Optimization in Task-Oriented NOMA Communications for Autonomous Vehicle Perception** (2024) — Carla E Garcia, Mario R Camana, Abuzar B Mohammad, Jorge Querol, Symeon Chatzinotas. In *2024 IEEE Wireless Communications and Networking Conference (WCNC)*. | Open Access: https://hdl.handle.net/10993/62712 URL: https://jorge.querol.org/publication/garcia-2024-edge/ - *Abstract*: The Internet of Vehicles (IoV) is undergoing swift advancements in capability and intelligence, poised to facilitate a diverse range of innovative applications. Within the IoV, edge learning empowers intelligent applications and services by leveraging data -driven tasks. Therefore, in this paper, we propose optimizing the edge learning error prediction within an edge-supported Non-Orthogonal Multiple Access (NOMA) in task-oriented communications. Specifically, we consider three autonomous vehicle perception tasks, called: object detection, traffic sign, and weather classification. For this purpose, we propose a novel approach based on the Particle Swarm Optimization (PSO) algorithm to jointly minimize the edge learning error and optimize power allocation variables. Moreover, we investigate alternative benchmark schemes, including Quantum Particle Swarm Optimization, Cuckoo Search, and Butterfly Op-timization algorithms. Satisfactorily, our simulations substantiate the superiority of the PSO algorithm over the baseline schemes, delivering superior performance with reduced computation time. 68. **Demonstration of Safe Electromagnetic Radiation Emitted by 5G Active Antenna Systems** (2024) — Sumit Kumar, Chandan Kumar Sheemar, Abdelrahman Astro, Jorge Querol, Symeon Chatzinotas. In *arXiv preprint arXiv:2406.07910*. | DOI: https://doi.org/10.48550/arxiv.2406.07910 URL: https://jorge.querol.org/publication/kumar-2024-demonstration/ - *Abstract*: The careful planning and safe deployment of 5G technologies will bring enormous benefits to society and the economy. Higher frequency, beamforming, and small-cells are key technologies that will provide unmatched throughput and seamless connectivity to 5G users. Superficial knowledge of these technologies has raised concerns among the general public about the harmful effects of radiation. Several standardization bodies are active to put limits on the emissions which are based on a defined set of radiation measurement methodologies. However, due to the peculiarity of 5G such as dynamicity of the beams, network densification, Time Division Duplexing mode of operation, etc, using existing EMF measurement methods may provide inaccurate results. In this context, we discuss our experimental studies aimed towards the measurement of radiation caused by beam-based transmissions from a 5G base station equipped with an Active Antenna System(AAS). We elaborate on the shortcomings of current measurement methodologies and address several open questions. Next, we demonstrate that using user-specific downlink beamforming, not only better performance is achieved compared to non-beamformed downlink, but also the radiation in the vicinity of the intended user is significantly decreased. Further, we show that under weak reception conditions, an uplink transmission can cause significantly high radiation in the vicinity of the user equipment. We believe that our work will help in clearing several misleading concepts about the 5G EMF radiation effects. We conclude the work by providing guidelines to improve the methodology of EMF measurement by considering the spatiotemporal dynamicity of the 5G transmission. 69. **Classification and Characterization of RFI Events for Passive Earth Observation Bands** (2024) — Adrian Perez-Portero, Jorge Querol, Adriano Camps. In *IGARSS 2024-2024 IEEE International Geoscience and Remote Sensing Symposium*. | Open Access: https://hdl.handle.net/10993/62570 URL: https://jorge.querol.org/publication/perez-2024-classification/ - *Abstract*: Passive Microwave remote sensing is a very energy-efficient and time-proven technology for remote sensing. Microwave Radiometry and Global Navigation Satellite System (GNSS)-Reflectometry are two widely-used examples. The increasing effects of Radio-Frequency Interferences (RFI) on the performance of these receivers have sparked serious concerns due to their proliferation. Detection and mitigation of RFI heavily rely on the identification and location of the interference sources. Due to the vast amount of degrees of freedom found in these RFIs, classification using classical signal processing techniques becomes problematic, especially if combined RFIs are found within the same bandwidth. In this work, continuous recordings of real RFI events from a real-time system to detect and locate RFI sources are used as training data for an automated classification system, the description and performance of which are presented and analyzed. 70. **Artificial Intelligence Satellite Telecommunication Testbed using Commercial Off-The-Shelf Chipsets** (2024) — Luis Manuel GARCES SOCARRAS, Amirhossein Nik, Flor de Guadalupe ORTIZ GOMEZ, Juan Andres VASQUEZ-PERALVO, Jorge Luis GONZALEZ RIOS, Mouhamad CHEHAITLY, Marcele OLIVEIRA KUHFUSS DE MENDONÇA, Eva Lagunas, Jan Thoemel, Sumit Kumar, Jorge Querol. In *AI in and for Space (ESA SPAICE 2024)*. | Open Access: https://hdl.handle.net/10993/62127 URL: https://jorge.querol.org/publication/garces-2024-artificial/ - *Abstract*: The Artificial Intelligence Satellite Telecommunications Testbed (AISTT), part of the ESA project SPAICE, is focused on the transformation of the satellite payload by using artificial intelligence (AI) and machine learning (ML) methodologies over available commercial off-the-shelf (COTS) AI-capable chips for onboard processing. The objectives include validating artificial intelligence-driven SATCOM scenarios such as interference detection, spectrum sharing, radio resource management, decoding, and beamforming. The study highlights hardware selection and payload architecture. Preliminary results show that ML models significantly improve signal quality, spectral efficiency, and throughput compared to conventional payload. Moreover, the testbed aims to evaluate the performance and the use of AI-capable COTS chips in onboard SATCOM contexts. 71. **Adaptive Carrier Aggregation for Enhanced Reliability in Multi-Band GEO Satellite Systems** (2024) — Mohammed Al-Ansi, Jorge Querol, Eva LAGUNAS, Joan Bas, Symeon CHATZINOTAS. In *IEEE International Symposium on Personal, Indoor and Mobile Radio Communications*. | Open Access: https://hdl.handle.net/10993/61964 URL: https://jorge.querol.org/publication/al-2024-adaptive/ - *Abstract*: Enhancing reliability in high-throughput satellites (HTS) operating in geostationary orbit (GEO) is critical, particularly under adverse channel conditions. This study investigates the potential of multi-connectivity (MC) enabled by carrier aggregation (CA) to improve the data rate, ensuring a high level of reliability of multi-band Ka/Ku GEO HTS systems. A system and channel model for the multi-band GEO satellite system is developed, and an inter-band CA algorithm is proposed. This algorithm dynamically adjusts the user link transmission scheme based on channel quality and user requirements, ranging from a single Ka-band connectivity to MC, utilizing both bands with CA via packet duplication or packet splitting. The numerical results in various weather scenarios validate the effectiveness of the algorithm, demonstrating significant improvements in system performance, reduced outage probability, and improved overall system reliability. These findings highlight the importance of MC and multi-band technologies in future 6G networks. 72. **A Study of Lunar Proximity Networks: Scenarios and Architectures** (2024) — Mouhamad CHEHAITLY, Houcine CHOUGRANI, Sumit KUMAR, Youssouf DRIF, Jorge Querol, Stefano PETRI, Leonardo TURCHI, Symeon CHATZINOTAS. In *The IEEE Wireless in Space and Extreme Environments*. | Open Access: https://hdl.handle.net/10993/62636 URL: https://jorge.querol.org/publication/chehaitly-2024-study/ - *Abstract*: High data rate, adaptive, inter networked proximity communications for Space, part of the ESA project PROSPECT, is focused on selecting the best-fit terrestrial technology for lunar proximity communications scenarios. This study explores the concept of lunar proximity networks, which play an essential role in enabling direct and short-range communication between devices on the lunar surface. The study is organized to analyze scenarios where these networks are applicable, the potential communication architectures, and the technologies that could be utilized. Furthermore, it includes a trade-off analysis that focuses on the lunar channel model and technology selection, followed by simulation results that offer valuable insights into the performance and feasibility of these networks. The study ends with recommendations for the design and implementation of lunar proximity networks, highlighting their pivotal role in future lunar missions to support the long-term human mission to the Moon. 73. **5G Non-Terrestrial Networks with OpenAirInterface: An Experimental Study over GEO Satellites** (2024) — Florian Völk, Thomas Schlichter, Sumit Kumar, Robert T. Schwarz, Andreas Knopp, Marwan Hammouda, Thomas Heyn, Jorge Querol, Symeon Chatzinotas, Adam Kapovits. In *IEEE Access*. | DOI: https://doi.org/10.1109/ACCESS.2024.3483958 | Open Access: https://hdl.handle.net/10993/62569 URL: https://jorge.querol.org/publication/volk-20245-g/ - *Abstract*: The 3rd Generation Partnership Project (3GPP) aims to integrate non-terrestrial networks (NTNs) with terrestrial 5G networks. In this context, prototyping and testing are essential to demonstrate the readiness of new 5G-NTN releases. However, commercial 5G protocol stack implementations are usually costly and closed solutions, which makes it challenging for universities and nonprofit research institutions to adapt and customize them for 5G-NTN testing and development purposes. Software-defined radio testbeds that utilize open-source software implementations are an attractive alternative. In this article, we describe our protocol stack adaptation of an open-source implementation for 5G-NTN based on OpenAirInterface (OAI), which runs on commodity hardware. We evaluate the performance of our 5G-NTN in various layers in real-world environments with a transparent geostationary satellite. We validate our testbed with a variety of Internet applications. These include streaming video, web browsing, and voice over IP. The results indicate that the current implementation utilizing the 5 MHz bandwidth is reliable over several hours and achieves both downlink and uplink speeds of 3.6 Mb/s while maintaining a typical geostationary latency of approximately 530 ms. The tests demonstrate that our 5G-NTN testbed is an reliable alternative to costly commercial implementations. 74. **System Analysis of Lunar Computations Communication Architectures** (2023) — Laura Chikosman, Miguel Angel OLIVARES MENDEZ, Juan Carlos MERLANO DUNCAN, Sumit Kumar, Chandan Kumar SHEEMAR, Symeon Chatzinotas, Loveneesh Rana, Andreas Hein, Youssouf Drif, Swetha Varadarajulu, Jorge Querol. In *Space Resources Week*. | Open Access: https://hdl.handle.net/10993/60144 URL: https://jorge.querol.org/publication/chikosman-2023-system/ - *Abstract*: This research contribution by Laura Chikosman, Miguel Angel OLIVARES MENDEZ, Juan Carlos MERLANO DUNCAN, Sumit Kumar et al. (2023), published in Space Resources Week, investigates "System Analysis of Lunar Computations Communication Architectures" within the domains of Satellite Communications, Signal Processing. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 75. **Single-and multi-connectivity for multi-satellite 6G communication networks** (2023) — Mohammed Al-Ansi, Jorge Querol, Eva Lagunas, Symeon Chatzinotas. In *IET Digital Library*. | Open Access: https://hdl.handle.net/10993/58289 URL: https://jorge.querol.org/publication/al-2023-single/ - *Abstract*: This study explores the connectivity strategies for downlink multi-satellites in 6G communication networks. We begin with concepts, technologies, and trade-offs of Single-Connectivity (SC) and Multi-Connectivity (MC). Within the realm of MC, we present three different scenarios, one of which serves as a case study with a particular emphasis on Dual Connectivity (DC). This DC is performed between Geostationary Earth Orbit (GEO) and Low Earth Orbit (LEO) satellites for public safety systems. To improve reliability, we consider packet duplication mechanisms in addition to multi-band satellite capabilities. This supports the LEO link, addresses its limited availability, and facilitates a smooth handover between LEO satellites. Using link-level simulation, outage probability is examined by comparing the SC and MC modes under normal and adverse weather conditions. The findings of this study pave the way for more research to enhance connectivity solutions for more reliable and efficient global communication networks by bringing to light the MC opportunities for multi-satellite systems. 76. **Signal Processing Based Antenna Pattern Characterization for MIMO Systems** (2023) — Chandan Kumar Sheemar, Jorge Querol, Symeon Chatzinotas. In *2023 International Conference on Software, Telecommunications and Computer*. | DOI: https://doi.org/10.23919/SoftCOM58365.2023.10271685 | Open Access: https://hdl.handle.net/10993/58107 URL: https://jorge.querol.org/publication/sheemar-2023-signal/ - *Abstract*: Sophisticated antenna technologies are constantly evolving to meet the escalating data demands projected for 6G and future networks. The characterization of these emerging antenna systems poses challenges that necessitate a reevaluation of conventional techniques, which rely solely on simple measurements conducted in advanced anechoic chambers. In this study, our objective is to introduce a novel endeavour for antenna pattern characterization (APC) in next-generation multiple-input-multiple-output (MIMO) systems by utilizing the potential of signal processing tools. In contrast to traditional methods that struggle with multi-path scenarios and require specialized equipment for measurements, we endeavour to estimate the antenna pattern by exploiting information from both line-of-sight (LoS) and non-LoS contributions. This approach enables antenna pattern characterization in complex environments without the need for anechoic chambers, resulting in substantial cost savings. Furthermore, it grants a much wider research community the ability to independently perform APC for emerging complex 6G antenna systems, without relying on anechoic chambers. Simulation results demonstrate the efficacy of the proposed novel approach in accurately estimating the true antenna pattern. 77. **Short-Packet Communication Assisted Reliable Control of UAV for Optimum Coverage Range** (2023) — Sourabh Solanki, Vibhum Singh, Sumit Gautam, Jorge Querol, Symeon Chatzinotas. In *ICC 2023-IEEE International Conference on Communications*. | DOI: https://doi.org/10.1109/ICC45041.2023.10279207 | Open Access: https://hdl.handle.net/10993/54730 URL: https://jorge.querol.org/publication/solanki-2023-short/ - *Abstract*: The reliability of command and control (C2) operation of the UAV is one of the crucial aspects for the success of UAV applications beyond 5G wireless networks. In this paper, we focus on the short-packet communication to maximize the coverage range of reliable UAV control. We quantify the reliability performance of the C2 transmission from a multi-antenna ground control station (GCS), which also leverages maximal-ratio transmission beamforming, by deriving the closed-form expression for the average block error rate (BLER). To obtain additional insights, we also derive the asymptotic expression of the average BLER in the high-transmit power regime and subsequently analyze the possible UAV configuration space to find the optimum altitude. Based on the derived average BLER, we formulate a joint optimization problem to maximize the range up to which a UAV can be reliably controlled from a GCS. The solution to this problem leads to the optimal resource allocation parameters including blocklength and transmit power while exploiting the vertical degrees of freedom for UAV placement. Finally, we present numerical and simulation results to corroborate the analysis and to provide various useful design insights. 78. **Robust Beamforming for IRS Aided MIMO Full Duplex Systems** (2023) — Chandan Kumar Sheemar, Jorge Querol, Sourabh Solanki, Sumit Kumar, Symeon Chatzinotas. In *GLOBECOM 2023-2023 IEEE Global Communications Conference*. | Open Access: https://hdl.handle.net/10993/58142 URL: https://jorge.querol.org/publication/sheemar-2023-robust/ - *Abstract*: In this paper, a novel robust beamforming for an intelligent reflecting surface (IRS) assisted FD system is presented. Since perfect channel state information (CSI) is often challenging to acquire in practice, we consider the case of imperfect CSI and adopt a statistically robust beamforming approach to maximize the ergodic weighted sum rate (WSR). We also analyze the achievable WSR of an IRS-assisted FD with imperfect CSI, for which the lower and the upper bounds are derived. The ergodic WSR maximization problem is tackled based on the expected Weighted Minimum Mean Squared Error (WMMSE), which is guaranteed to converge to a local optimum. The effectiveness of the proposed design is investigated with extensive simulation results. It is shown that our robust design achieves significant performance gain compared to the naive beamforming approaches and considerably outperforms the robust Half-Duplex (HD) system. 79. **Radio Communication Blackout Mitigation: Ray Tracing Analysis and Signal Characterization Including Experimental Validation for Non-magnetized Plasmas** (2023) — Johannes Laur, Diana Luis, Alan Viladegut, Vincent F Giangaspero, Andrea Lani, Jorge Luis González Rios, Jorge Querol, J Peralvo, J Merlano Duncan, AM Hein. In *AEC 2023-10th EUCASS-9th CEAS*. | Open Access: https://hdl.handle.net/10993/67963 URL: https://jorge.querol.org/publication/laur-2023-radio/ - *Abstract*: Atmospheric entries and hypersonic flights are challenging. The bow shock in front of the vehicle and friction heat the gas flow around the vehicle and result in the ionization of molecules and atoms. This plasma surrounding the spacecraft leads to a total or partial cut-off of radio communication for telecommand, telemetry, and navigation if the plasma frequency is near or exceeds the radio frequency of the communication system. Recent improvements in high-temperature superconducting materials brought back the focus on the magnetic windowing radio communication blackout mitigation method. Within the Horizon 2020 MEESST (Magnetohydrodynamic Enhanced Entry System for Space Transportation) project the effect of an applied magnetic field using a superconductive magnet with a sufficiently strong magnetic field is analyzed. The BlackOut Ray-Tracer (BORAT) was further developed to predict the wave propagation in the plasma in two dimensions for magnetized plasma using the Eikonal solver. A signal characterization model was added for a better understanding of the physics of wave propagation. The latest results for non-magnetized plasma show a good agreement between the numerical solutions and the experiment. The signal characterization allows us to further define brownout scenarios with partially disrupted communication. The effect of a weak applied magnetic field on the ray propagation path and the signal characteristics are discussed leading to the conclusion that the magnetic windowing method is promising to mitigate radio blackout when strong magnetic fields are applied. 80. **Per-link Parallel and Distributed Hybrid Beamforming for Multi-Cell Massive MIMO Millimeter Wave Full Duplex** (2023) — Chandan Kumar Sheemar, Symeon Chatzinotas, Dirk Slock, Eva Lagunas, Jorge Querol. In *Authorea Preprints*. | DOI: https://doi.org/10.36227/techrxiv.21904665 | Open Access: https://hdl.handle.net/10993/62460 URL: https://jorge.querol.org/publication/sheemar-2023-per/ - *Abstract*: Full duplex (FD) is an auspicious wireless technology that holds the potential to double data rates through simultaneous transmission and reception. This paper proposes two innovative designs of hybrid beamforming (HYBF) for a multicell massive multiple-input-multiple-output (mMIMO) millimeter wave (mmWave) FD system. Initially, we introduce a novel centralized HYBF (C-HYBF) scheme, which employs the minorization-maximization (MM) method. However, while centralized beamforming designs offer superior performance, they suffer from high computational complexity, substantial communication overhead, and demand expensive computational resources. To surmount these challenges, we present a framework that facilitates per-link parallel and distributed HYBF (P$\&$D-HYBF) in the mmWave frequency band. This cooperative approach enables each base station (BS) to independently solve its local, low-complexity sub-problems in parallel, resulting in a substantial reduction in communication overhead and computational complexity. Simulation results demonstrate that P$\&$D-HYBF achieves comparable performance to C-HYBF, and with only a few radio-frequency (RF) chains, both designs surpass the capabilities of fully digital half duplex (HD) systems. 81. **Onboard processing in satellite communications using ai accelerators** (2023) — Flor Ortíz, Víctor Monzón Baeza, Luis Manuel Garcés-Socarrás, Juan A. Vásquez-Peralvo, Jorge Luis González Ríos, Gianluca Fontanesi, Eva Lagunas, Jorge Querol, Symeon Chatzinotas. In *Aerospace*. | DOI: https://doi.org/10.3390/AEROSPACE10020101 | Open Access: https://hdl.handle.net/10993/54478 URL: https://jorge.querol.org/publication/ortiz-2023-onboard/ - *Abstract*: Satellite communication (SatCom) systems operations centers currently require high human intervention, which leads to increased operational expenditure (OPEX) and implicit latency in human action that causes degradation in the quality of service (QoS). Consequently, new SatCom systems leverage artificial intelligence and machine learning (AI/ML) to provide higher levels of autonomy and control. Onboard processing for advanced AI/ML algorithms, especially deep learning algorithms, requires an improvement of several magnitudes in computing power compared to what is available with legacy, radiation-tolerant, space-grade processors in space vehicles today. The next generation of onboard AI/ML space processors will likely include a diverse landscape of heterogeneous systems. This manuscript identifies the key requirements for onboard AI/ML processing, defines a reference architecture, evaluates different use case scenarios, and assesses the hardware landscape for current and next-generation space AI processors. 82. **MEC-assisted low latency communication for autonomous flight control of 5G-connected UAV** (2023) — Sourabh Solanki, Asad Mahmood, Vibhum Singh, Sumit Gautam, Jorge Querol, Symeon Chatzinotas. In *2023 IEEE 97th Vehicular Technology Conference (VTC2023-Spring)*. | DOI: https://doi.org/10.1109/VTC2023-Spring57618.2023.10200917 | Open Access: https://hdl.handle.net/10993/54731 URL: https://jorge.querol.org/publication/solanki-2023-mec/ - *Abstract*: Proliferating applications of unmanned aerial vehicles (UAVs) impose new service requirements, leading to several challenges. One of the crucial challenges in this vein is to facilitate the autonomous navigation of UAVs. Concretely, the UAV needs to individually process the visual data and subsequently plan its trajectories. Since the UAV has limited onboard storage constraints, its computational capabilities are often restricted and it may not be viable to process the data locally for trajectory planning. Alternatively, the UAV can send the visual inputs to the ground controller which, in turn, feeds back the command and control signals to the UAV for its safe navigation. However, this process may introduce some delays, which is not desirable for autonomous UAVs’ safe and reliable navigation. Thus, it is essential to devise techniques and approaches that can potentially offer low-latency solutions for planning the UAV’s flight. To this end, this paper analyzes a multi-access edge computing aided UAV and aims to minimize the latency of the task processing. More specifically, we propose an offloading strategy for a UAV by optimally designing the offloading parameter, local computational resources, and altitude of the UAV. The numerical and simulation results are presented to offer various design insights, and the benefits of the proposed strategy are also illustrated in contrast to the other baseline approaches. 83. **Location dependent allocation of timers and buffers at layer-2 in LEO based 5G-NTN** (2023) — Chandan Kumar Sheemar, Sumit Kumar, Jorge Querol, Symeon Chatzinotas. In *IET Conference Proceedings CP873*. | Open Access: https://hdl.handle.net/10993/58108 URL: https://jorge.querol.org/publication/sheemar-2023-location/ - *Abstract*: The integration of Terrestrial Networks (TN) and Non-Terrestrial Networks (NTN), primarily utilizing satellites, has gained significant attention due to the potential of NTN to provide widespread coverage. The unique physical layer properties of 5G-NR offer the possibility of direct access to 5G services through satellites. However, the substantial Round-Trip Delays (RTD) associated with NTNs necessitate a re-evaluation of the design of timers and buffers in the radio link control (RLC) and packet data convergence protocol (PDCP) layers. This is particularly crucial for regenerative payload satellites with limited computational resources that require optimal utilization of the available resources. This research aims to explore the integration of emerging NTNs with limited resources from a higher-layer perspective. We propose a novel and efficient method for designing the buffers and timers in the RLC and PDCP layers without the need for intensive computations. Since the optimal solution depends on the RTD, which might result to be different for users located at different spots of the satellite beam, a user location-dependent approach is adopted. This approach is particularly relevant for efficiently utilizing the available limited resources and avoiding unnecessary delays in the system. Through simulations, we demonstrate that the proposed methods significantly improve performance in terms of resource utilization and reducing delays. 84. **Localization as a key enabler of 6G wireless systems: A comprehensive survey and an outlook** (2023) — Stylianos E. Trevlakis, Alexandros-Apostolos A. Boulogeorgos, Dimitrios Pliatsios, Jorge Querol, Konstantinos Ntontin, Panagiotis Sarigiannidis, Symeon Chatzinotas, Marco Di Renzo. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2023.3324952 | Open Access: https://hdl.handle.net/10993/58652 URL: https://jorge.querol.org/publication/trevlakis-2023-localization/ - *Abstract*: When fully implemented, sixth generation (6G) wireless systems will constitute intelligent wireless networks that enable not only ubiquitous communication but also high-accuracy localization services. They will be the driving force behind this transformation by introducing a new set of characteristics and service capabilities in which location will coexist with communication while sharing available resources. To that purpose, this survey investigates the envisioned applications and use cases of localization in future 6G wireless systems, while analyzing the impact of the major technology enablers. Afterwards, system models for millimeter wave, terahertz and visible light positioning that take into account both line-of-sight (LOS) and non-LOS channels are presented, while localization key performance indicators are revisited alongside mathematical definitions. Moreover, a detailed review of the state of the art conventional and learning-based localization techniques is conducted. Furthermore, the localization problem is formulated, the wireless system design is considered and the optimization of both is investigated. Finally, insights that arise from the presented analysis are summarized and used to highlight the most important future directions for localization in 6G wireless systems. 85. **Implementation of Edge-driven Geofencing and BVLOS Control for 5G-enabled Delivery Drone** (2023) — Abhishek Bera, Youssouf Drif, Jorge Querol, Miguel Olivares-Mendez. In *2023 IEEE Globecom Workshops (GC Wkshps)*. | Open Access: https://hdl.handle.net/10993/62634 URL: https://jorge.querol.org/publication/bera-2023-implementation/ - *Abstract*: Drone-assisted applications have gained significant attention in both academic and industrial research and development. The utilization of advanced technologies like 5G and edge computing plays a vital role in facilitating the capabilities of these drone applications. Time-critical drone applications can be effectively supported by leveraging the high-bandwidth connectivity provided by 5G networks. Moreover, the integration of edge offloading addresses the challenge of limited onboard processing power in drone operations. This paper demonstrates the requirements and implementation of drone, edge, and 5G technology use case scenarios. Specifically, we focus on implementing a dynamic geofencing algorithm and beyond visual line of sight (BVLOS) control for the delivery drone use case in a real system using 5G, exploiting the use of edge computing to extend the onboard processing power of the drone. Finally, the obtained results and accompanying videos provide concrete evidence of the applicability of edge-driven 5G-enabled drones in drone-assisted use-case scenarios. 86. **IRS Assisted MIMO Full Duplex: Rate Analysis and Beamforming Under Imperfect CSI** (2023) — Chandan Kumar Sheemar, Sourabh Solanki, Jorge Querol, Sumit Kumar, Symeon Chatzinotas. In *IEEE Open Journal of the Communications Society*. | DOI: https://doi.org/10.1109/OJCOMS.2023.3306524 | Open Access: https://hdl.handle.net/10993/58102 URL: https://jorge.querol.org/publication/sheemar-2023-irs/ - *Abstract*: Intelligent reflecting surfaces (IRS) have emerged as a promising technology to enhance the performance of wireless communication systems. By actively manipulating the wireless propagation environment, IRS enables efficient signal transmission and reception. In recent years, the integration of IRS with full-duplex (FD) communication has garnered significant attention due to its potential to further improve spectral and energy efficiencies. IRS-assisted FD systems combine the benefits of both IRS and FD technologies, providing a powerful solution for the next generation of cellular systems. In this manuscript, we present a novel approach to jointly optimize active and passive beamforming in a multiple-input-multiple-output (MIMO) FD system assisted by an IRS for weighted sum rate (WSR) maximization. Given the inherent difficulty in obtaining perfect channel state information (CSI) in practical scenarios, we consider imperfect CSI and propose a statistically robust beamforming strategy to maximize the ergodic WSR. Additionally, we analyze the achievable WSR for an IRS-assisted MIMO FD system under imperfect CSI by deriving both the lower and upper bounds. To tackle the problem of ergodic WSR maximization, we employ the concept of expected weighted minimum mean squared error (EWMMSE), which exploits the information of the expected error covariance matrices and ensures convergence to a local optimum. We evaluate the effectiveness of our proposed design through extensive simulations. The results demonstrate that our robust approach yields significant performance improvements compared to the simplistic beamforming approach that disregards CSI errors, while also outperforming the robust half-duplex (HD) system considerably. 87. **Genetic Algorithm-based Beamforming in Subarray Architectures for GEO Satellites** (2023) — Juan Andrés Vásquez-Peralvo, Jorge Querol, Eva Lagunas, Flor Ortiz, Luis Manuel Garcés-Socarrás, Jorge Luis González-Rios, Victor Monzon Baeza, Symeon Chatzinotas. In *arXiv e-prints*. | Open Access: https://hdl.handle.net/10993/62760 URL: https://jorge.querol.org/publication/andres-2023-genetic/ - *Abstract*: The incorporation of subarrays in Direct Radiating Arrays for satellite missions is fundamental in reducing the number of Radio Frequency chains, which correspondingly diminishes cost, power consumption, space, and mass. Despite the advantages, previous beamforming schemes incur significant losses during beam scanning, particularly when hybrid beamforming is not employed. Consequently, this paper introduces an algorithm capable of compensating for these losses by increasing the power, for this, the algorithm will activate radiating elements required to address a specific Effective Isotropic Radiated Power for a beam pattern over Earth, projected from a GeoStationary satellite. In addition to the aforementioned compensation, other beam parameters have been addressed in the algorithm, such as beamwidth and Side Lobe Levels. To achieve these objectives, we propose employing the array thinning concept through the use of genetic algorithms, which enable beam shaping with the desired characteristics and power. The full array design considers an open-ended waveguide, configured to operate in circular polarization within the Ka-band frequency range of 17.7-20.2 GHz. 88. **Full-duplex-enabled joint communications and sensing with reconfigurable intelligent surfaces** (2023) — Chandan Kumar Sheemar, George C. Alexandropoulos, Dirk Slock, Jorge Querol, Symeon Chatzinotas. In *2023 31st European Signal Processing Conference (EUSIPCO)*. | DOI: https://doi.org/10.23919/EUSIPCO58844.2023.10289881 URL: https://jorge.querol.org/publication/sheemar-2023-full/ - *Abstract*: The full-duplex (FD) technology has the potential to radically evolve wireless systems, facilitating the integration of both communications and radar functionalities into a single device, thus, enabling joint communication and sensing (JCAS). In this paper, we present a novel approach for JCAS that incorporates a reconfigurable intelligent surface (RIS) in the near-field of an FD multiple-input multiple-output (MIMO) node, which is jointly optimized with the digital beamformers to enable JSAC and efficiently handle self-interference (SI). We propose a novel problem formulation for FD MIMO JCAS systems to jointly minimize the total received power at the FD node's radar receiver, while maximizing the sum rate of downlink communications subject to a Cramer-Rao bound (CRB) constraint. In contrast to the typically used CRB in the relevant literature, we derive a novel, more accurate, target estimation bound that fully takes into account the RIS deployment. The considered problem is solved using alternating optimization, which is guaranteed to converge to a local optimum. The simulation results demonstrate that the proposed scheme achieves significant performance improvement both for communications and sensing. It is showcased that, jointly designing the FD MIMO beamformers and the RIS phase configuration to be SI aware can significantly loosen the requirement for additional SI cancellation. 89. **Flexible beamforming for direct radiating arrays in satellite communications** (2023) — Juan Andrés Vásquez-Peralvo, Jorge Querol, Flor Ortíz, Jorge Luis González Rios, Eva Lagunas, Victor Monzon Baeza, Gianluca Fontanesi, Luis Manuel Garcés-Socorrás, Juan Carlos Merlano Duncan, Symeon Chatzinotas. In *IEEE Access*. | DOI: https://doi.org/10.1109/ACCESS.2023.3300039 | Open Access: https://hdl.handle.net/10993/58212 URL: https://jorge.querol.org/publication/vasquez-2023-flexible/ - *Abstract*: Onboard satellite communication systems generate and manage coverage beams over the Earth. Depending on data traffic requirements, the number of beams, side lobe levels, nulls, and EIRP, their beamwidth must be efficiently generated and managed. Therefore, this paper describes an approach for beam pattern synthesis applied to geostationary satellite communication systems. The beam pattern synthesis can generate beams with a beamwidth variation from 0.45° to 1.5°, which can be controlled independently for the two principal cuts. In addition, other requirements have been considered, e.g., latitude, and longitude, required EIRP, minimum and maximum side love levels for the two principal cuts, and nulling direction. The output of the synthesizer is a weight matrix with beamforming coefficients of the required beam. The direct radiating array in this contribution utilizes an open-ended waveguide antenna as unit cell elements with a period of 0.875λ0designed to work in left-hand circular polarization in the frequency band from 17.7 to 20.1 GHz. Since this design is intended for high-data rates applications, the minimum beamwidth requirements are very narrow. Therefore, 36 × 36 sub-arrays of 4 × 4 unit cells with a period of 3.5λ are considered to accomplish the beamwidth requirements while maintaining reduced computational and time resources for the weight matrix calculation compared to the conventional counterpart of 144×144 unit cells. The results show that the algorithm, which uses the surrogate optimizer, can compute the weight matrix and synthesize the beam with a slight deviation from the input data. 90. **Flexible Payload Configuration for Satellites using Machine Learning** (2023) — Marcele OLIVEIRA KUHFUSS DE MENDONÇA, Flor de Guadalupe ORTIZ GOMEZ, Jorge Querol, Eva Lagunas, Juan Andres VASQUEZ-PERALVO, Victor MONZON BAEZA, Symeon Chatzinotas, Björn OTTERSTEN. In *IEEE International Conference on Machine Learning for Communication*. | Open Access: https://hdl.handle.net/10993/58800 URL: https://jorge.querol.org/publication/oliveira-2023-flexible/ - *Abstract*: Satellite communications, essential for modern connectivity, extend access to maritime, aeronautical, and remote areas where terrestrial networks are unfeasible. Current GEO systems distribute power and bandwidth uniformly across beams using multi-beam footprints with fractional frequency reuse. However, recent research reveals the limitations of this approach in heterogeneous traffic scenarios, leading to inefficiencies. To address this, this paper presents a machine learning (ML)-based approach to Radio Resource Management (RRM).We treat the RRM task as a regression ML problem, integrating RRM objectives and constraints into the loss function that the ML algorithm aims at minimizing. Moreover, we introduce a context-aware ML metric that evaluates the ML model’s performance but also considers the impact of its resource allocation decisions on the overall performance of the communication system. 91. **Experimental Study of the Effects of RLC Modes for 5G-NTN applications using OpenAirInterface5G** (2023) — Sumit Kumar, Chandan Kumar Sheemar, Jorge Querol, Amirhossein Nik, Symeon Chatzinotas. In *2023 IEEE Globecom Workshops (GC Wkshps)*. | Open Access: https://hdl.handle.net/10993/58936 URL: https://jorge.querol.org/publication/kumar-2023-experimental/ - *Abstract*: Provisioning of 5G services via Non-Terrestrial Networks (5G-NTN) has become a reality. Currently, 5G-NTN is being developed by adapting the 5G Terrestrial Network (5G-TN) protocol which presents several challenges as the satellite channel is significantly different from terrestrial channels. The retransmission mechanism is one of them. Recent works on 5G-NTN have followed the approach of disabling retransmissions from the 5G protocol stack such as Hybrid Automatic Repeat Request (HARQ) at the MAC layer and Automatic Repeat Request (ARQ) at the RLC layer while delegating it to the application layer. This approach degrades the end-user-throughput and latency. In this work, we experimentally study the effect of enabling ARQ retransmission, by using RLC Acknowledged Mode (RLC-AM) in a GEO-based 5G-NTN which is susceptible to packet loss caused by low SNR. We conduct realtime experiments to compare the effects of RLC-AM and RLC Unacknowledged Mode(RLC-Um)on applications(VoIP, video stream, file transfer) using TCP and UDP for different SNR regimes. We have used OpenAirInterface5G-NTN, which is developed to perform realtime 5G-NTN experiments, and a satellite channel emulator. We observe that for low SNR, RLC-AM performs better than RLC-UM in achieving the required bitrate and packet error rate. The reason being RLC-AM recovers the lost packets earlier in the protocol stack without delegating the retransmissions to the application layer. This becomes especially useful when HARQ is disabled. We believe that our experimental study will complement the ongoing theoretical research and help improve the procedures of the Radio Resource Control(RRC) layer in 5G-NTN-specific applications. 92. **End-to-end performance evaluation of slp waveforms** (2023) — Jevgenij Krivochiza, Juan Carlos Merlano Duncán, Jorge Querol, Symeon Chatzinotas. In *IEEE Access*. | DOI: https://doi.org/10.1109/ACCESS.2023.3327643 | Open Access: https://hdl.handle.net/10993/57343 URL: https://jorge.querol.org/publication/krivochiza-2023-end/ - *Abstract*: In this paper, we investigate the demodulation and decoding of the symbol-level precoded (SLP) signal using the conventional logarithmic likelihood ratio (LLR) and low-density parity check (LDPC) decoding algorithms operating in real-time on the software-defined radio (SDR) receiver. Its conventional forward error correction (FEC) is designed assuming symmetric additive white Gaussian noise (AWGN). While SLP generates asymmetric constellation point clouds it is unclear if it can achieve similar FEC gains in an end-to-end coded setup. The receiver is implemented based on the DVB-S2X standard. It estimates multi-beam interference-limited channel coefficients by using the orthogonal pilots embedded into the DVB-S2X frames to facilitate precoding at the transmitter. After the received frames are fully synchronized the payload symbols are decoded in two stages: soft decision using the LLR and hard decision using the LDPC decoders. We benchmark the bit error rate (BER) and frame error rate (FER) of the complete decoding chain while using the zero-forcing (ZF) and the selected SLP channel-interference canceling techniques. The conducted in-lab experiments show that the SLP can improve BER and FER performance in the conventional receiving and decoding design for symmetric constellations while achieving its original optimization goals. 93. **Doppler effect mitigation in LEO-based 5G non-terrestrial networks** (2023) — Ashish Kumar Meshram, Sumit Kumar, Jorge Querol, Symeon Chatzinotas. In *2023 IEEE Globecom Workshops (GC Wkshps)*. | Open Access: https://hdl.handle.net/10993/58801 URL: https://jorge.querol.org/publication/meshram-2023-doppler/ - *Abstract*: In recent years, integrating Non-Terrestrial Networks (NTN) components with 5G Terrestrial Networks (TN) has led to considerable attention from academia and industry, leading to the standardization of 5G-NTN in 3GPP. Among the various NTN solutions, a notable one is the Low Earth Orbit (LEO)-based 5G-NTN with a regenerative payload. This system stands out because it can provide latency and throughput levels similar to terrestrial 5G networks. However, a significant challenge in this integration arises from the substantial Doppler effect caused by the rapid movement of LEO satellites. This effect must be effectively addressed to establish a successful data link between the User Equipment (UE) and the gNodeB (gNB). This study proposes a simple yet efficient method to tackle this issue. The method involves using a regenerative LEO satellite-based 5G gNB, which pre-compensates the Doppler frequency with respect to its beam center before initiating any data transmission. Subsequently, the UE performs post-compensation to handle residual Doppler frequency and achieve accurate initial synchronization. We evaluated the performance through simulations and demonstrated the effectiveness of the proposed system. The results indicate successful mitigation of Doppler effects, facilitating seamless communication between LEO satellite-based 5G NTN. 94. **Beam centric Doppler pre-compensation for LEO-based 5G-NTN** (2023) — Ashish Kumar Meshram, Sumit Kumar, Jorge Querol, Symeon Chatzinotas. In *IET Digital Library*. | Open Access: https://hdl.handle.net/10993/58790 URL: https://jorge.querol.org/publication/meshram-2023-beam/ - *Abstract*: Integration of Non-Terrestrial Networks (NTN) components with 5G Terrestrial Networks (TN) is getting sig- nificant traction from academia and industry, resulting in the standardization of 5G-NTN in 3GPP. Low Earth Orbit (LEO) based 5G-NTN, especially regenerative payload, are of particular interest as they can provide latency and throughput comparable to terrestrial 5G networks. Initial synchronization is the first step when a User Equipment (UE) attempts to establish a data link with the gNB. However, the excessive Doppler caused by the LEO satellite's fast movement must be exclusively compensated before the UE can successfully align time and frequency. This work presents an effective method to address this issue. In this method, a regenerative LEO satellite-based 5G gNodeB (gNB) pre-compensates the Doppler with respect to its Beam Center (BC) before any transmission. Further, a UE post-compensates the residual Doppler to achieve successful initial synchronization. With the proposed methodology, we expect the accuracy of initial synchronization to be comparable to 5G-TN without increasing the processing complexity at the UE. Furthermore, for the realistic scenario, our analysis includes the effect of the LEO satellite trajectory error sphere and pointing error. 95. **Adaptive Timers and Buffer Optimization for Layer-2 Protocols in 5G Non-Terrestrial Networks** (2023) — Chandan Kumar Sheemar, Sumit Kumar, Jorge Querol, Symeon Chatzinotas. In *2023 International Conference on Software, Telecommunications and Computer*. | Open Access: https://hdl.handle.net/10993/58103 URL: https://jorge.querol.org/publication/sheemar-2023-adaptive/ - *Abstract*: Interest in the integration of Terrestrial Networks (TN) and Non-Terrestrial Networks (NTN); primarily satellites; has been rekindled due to the potential of NTN to provide ubiquitous coverage. Especially with the peculiar and flexible physical layer properties of 5G-NR, now direct access to 5G services through satellites could become possible. However, the large Round-Trip Delays (RTD) in NTNs require a re-evaluation of the design of RLC and PDCP layers timers (and associated buffers), in particular for the regenerative payload satellites which have limited computational resources, and hence need to be optimally utilized. Our aim in this work is to initiate a new line of research for emerging NTNs with limited resources from a higher-layer perspective. To this end, we propose a novel and efficient method for optimally designing the RLC and PDCP layers’ buffers and timers without the need for intensive computations. This approach is relevant for low-cost satellites, which have limited computational and energy resources. The simulation results show that the proposed methods can significantly improve the performance in terms of resource utilization and delays. 96. **5G Positioning Reference Signal Configuration for Integrated Terrestrial/Non-Terrestrial Network Scenario** (2023) — Alejandro Gonzalez-Garrido, Jorge Querol, Symeon Chatzinotas. In *2023 IEEE/ION Position, Location and Navigation Symposium (PLANS)*. | Open Access: https://hdl.handle.net/10993/58324 URL: https://jorge.querol.org/publication/gonzalez-20235-g/ - *Abstract*: The Fifth Generation (5G) New Radio offers a new Positioning, Navigation, and Timing (PNT) service with larger signal bandwidth and higher frequency carriers than previous generations, delivering more accurate measurements. This allows other vertical industries to benefit from this feature, opening up new possibilities. Furthermore, the 5G network includes Non-Terrestrial Network (NTN) elements such as Unmanned Aerial Vehicle (UAV), High-Altitude Platform Systems (HAPS), and satellites, which are gaining significant attention from the industry to allow for global communication. The future 6G aims to create a single network entity with multiple connectivity layers for all devices in all scenarios. Therefore, when combining both aspects of the 5G networks, the PNT service, and the NTN, there are several benefits such as: an independent and complete communication and navigation system under a single network, higher accuracy on the PNT solution than previous generation, global coverage for join navigation and communication, higher resilience on the positioning estimation, or new services offered. However, this is not free of challenges, as it is expected to achieve an accuracy, at least, similar to Global Navigation Satellite System (GNSS). One of the challenges is the multiplexing of the data and positioning service using a single infrastructure such a satellite. This paper has the purpose of analysing the effect in the accuracy of a delay estimator when a satellite constellation send a Positioning Reference Signal (PRS). Assuming that all satellites share the same frequency carrier and are synchronised between them. This 5G PRS main characteristic is its flexibility in terms of resource usage such as bandwidth, resource element density, symbols periodicity, a muting scheme, etc. This flexibility will be exploited in this paper to get a UE capable to estimate the Downlink Observed Time Difference of Arrival (DL-OTDoA) of the signal. Two challenges are present in this work, both are related to the characteristics of the RF channel between the Next Generation Base Station (gNB) and the User Equipment (UE): the first one is how the UE will cope with the high Doppler shift due to the high speed of the Low Earth Orbit (LEO) gNB increasing the Inter-Carrier Interference (ICI); and the second challenge is the effect of variable delay between OFDM symbols in the same slot and transmitter, increasing the effect of Intersymbol Interference (ISI). The contribution of the authors on this paper is the analysis of different PRS configuration that keeps a low interfere level between the moving gNBs. The result of this research highlight the impact that the length in number of subcarriers and number of OFDM symbol has in the accuracy of the delay estimation. It shows a trade-off in the constellation design, as a higher number of satellites in visibility also increase the ICI and ISI. 97. **5G NTN LEO based demonstrator using OpenAirInterface5G** (2023) — Sumit Kumar, Chandan Kumar Sheemar, Jorge Querol, Turker Yilmaz, Symeon Chatzinotas, Marwan Hammouda, Thomas Heyn, Thomas Schlichter, Paulo Marques, Luis Pereira. In *ICSSC*. | Open Access: https://hdl.handle.net/10993/58109 URL: https://jorge.querol.org/publication/kumar-20235-g/ - *Abstract*: 3GPP Release-17 formally recognizes Non- Terrestrial Network (NTN) components as an integral part of future telecommunication networks. The integration of 5G with NTN has gained significant traction due to the joint effort from academia, industry, and government space agencies. The first phase of 5G-NTN prototype development has been successful using GEO satellites. Moving ahead, LEO satellites can provide higher data rates and lower latency compared to GEO. In this paper, we discuss the 3GPP Release-17 compliant cross-layered adaptations done in OpenAirInterface5G during the project 5G-LEO (OpenAirInterface5G Extension for 5G Satellite Links). 5G-LEO aims to provide direct access to 5G services to a ground UE via a transparent payload LEO satellite. To the best of our knowledge, 5G-LEO is the first work involving the adaptation of 5G protocol addressing the challenges presented by the LEO satellite channel for example high and time-varying Doppler, Round-Trip-Time; and frequent handover. A Software Defined Radio-based end-to-end demonstrator has been developed during the project. Results from the experiments conducted during functional validation over the demonstrator are presented in this work. Our initial experiments show promising results and the feasibility of direct access to 5G services through transparent payload LEO satellites. 98. **RFI detection and mitigation for advanced correlators in interferometric radiometers** (2022) — Adrián Pérez-Portero, Jorge Querol, Adriano Camps, Manuel Martín‐Neira, Martin Süess, Juan Ignacio Ramirez, Alberto Zurita, Joséep Closa, Roger Oliva, R. Onrubia. In *Remote Sensing*. | DOI: https://doi.org/10.3390/RS14184672 URL: https://jorge.querol.org/publication/perez-2022-rfi/ - *Abstract*: This work presents the first RFI detection and mitigation algorithm for the interferometric radiometers that will be implemented in its correlator unit. The algorithm operates in the time and frequency domains, applying polarimetric and statistical tests in both domains, and exhibiting a tunable and arbitrary low probability of false alarm. It is scalable to a configurable number of receivers, and it is optimized in terms of quantization bits and the implementation of the cross-correlations in the time or frequency domains for hardware resource saving. New features of this algorithm are the computation of the Stokes parameters per frequency bin in the Short-Time Fourier Transform and a new parameter called Polarimetric Kurtosis. If RFI is detected in one domain or in both, it is removed using the calculated blanking masks. The optimum algorithm parameters are computed, such as length of the FFTs, the threshold selection for a given probability of false alarm, and the selection of the blanking masks. Last, an important result refers to the application of Parseval’s theorem for the computation of the cross-correlations in the frequency domain, instead of in the time domain, which is more efficient and leads to smaller errors even when using moderate quantization levels. The algorithm has been developed in the framework of the ESA’s technology preparation for a potential L-band radiometer mission beyond SMOS. However, it is also applicable to (polarimetric) real aperture radiometers, and its performance would improve if more than one bit is used in the signal quantization. 99. **OpenAirInterface as a platform for 5G-NTN Research and Experimentation** (2022) — Sumit Kumar, Ashish Kumar Meshram, Abdelrahman Astro, Jorge Querol, Thomas Schlichter, Guido Casati, Thomas Heyn, Florian Völk, Robert T. Schwarz, Andreas Knopp, Paulo Marques, Luis Pereira, Roberto Magueta, Adam Kapovits, Florian Kaltenberger. In *2022 IEEE Future Networks World Forum (FNWF)*. | DOI: https://doi.org/10.1109/FNWF55208.2022.00094 | Open Access: https://hdl.handle.net/10993/53157 URL: https://jorge.querol.org/publication/kumar-2022-openairinterface/ - *Abstract*: Technical advancements and experimental works for the integration of 5G and Non-Terrestrial Networks (NTN) have gained significant traction over the past few years. NTN components have been officially included in the 5G ecosystem by 3GPP in the latest Release-17. 5G-NTN research is ongoing and it is desirable to have a platform that facilitates quick prototyping of the proof-of-concept methods. OpenAirInterface(OAI) is an open-source experimental yet 3GPP standard-compliant Software Defined Radio (SDR) based protocol stack that has been widely known for implementing 4G/5G technologies. Due to its proven capabilities and flexibility, OAI is currently in the developmental process of integrating adaptations for the 5G-NTN. In this work, we discuss the peculiar features of OAI which are shaping it towards becoming a preferred tool for research and experimentation related to 5G-NTN. We provide details of completed/ongoing 5G-NTN projects leveraging OAI to achieve their objectives. In particular, we discuss 5G-GOA and 5G-LEO where critical adaptations in OAI are being done to support 5G-NTN use-cases. Such adaptations enable direct-access between UE and gNB via transparent payload Geostationary (5G-GOA) and Non-geostationary satellites (5G-LEO). Both projects have closely followed 3GPP discussions over 5G-NTN and the adaptations are compliant with the currently frozen 3GPP Release-17. OAI adaptations from both projects will be merged into the main development branch of OAI. We also provide a future roadmap of OAI towards 5G-NTN development. We believe that the pioneering steps taken in the course of the aforementioned projects will establish OAI as a preferred tool for 5G-NTN research and experimentations. 100. **Non-terrestrial network testbeds for 5G and beyond** (2022) — Jorge Querol, Sumit Kumar, Oltjon Kodheli, Abdelrahman Astro, Juan Duncan, Mohammad Gholamian, Rakesh Palisetty, Symeon Chatzinotas, Thomas Heyn, Guido Casati. In chapter. | DOI: https://doi.org/10.1049/pbte105e_ch16 URL: https://jorge.querol.org/publication/querol-2022-non/ - *Abstract*: The fifth generation (5G) of wireless communications offers a plethora of new communications paradigms, scenarios, and services. Among them, the integration of terrestrial and non-terrestrial networks is one of the most relevant aiming at providing seamless ubiquity connectivity and economies of scale for satellite communications. This chapter presents the most relevant experimental testbeds for the demonstration of 5G and beyond 5G adaptations for their use in non-terrestrial networks. In the first sections, a state-of-the-art review is presented including a description of the principal hardware and software components, highlighting OpenAirInterface as the most prominent open-source 5G stack. The latest sections describe the features and capabilities of the most advanced 5G non-terrestrial network testbeds based on OpenAirInterface: the 5G-SpaceLab and the 5G-Lab. 101. **Non-coherent massive MIMO integration in satellite communication** (2022) — V.M. Baeza, V.N. Ha, Jorge Querol, S. Chatzinotas. In *39th International Communications Satellite Systems Conference (ICSSC*. | Open Access: https://hdl.handle.net/10993/52126 URL: https://jorge.querol.org/publication/baeza-2022-non/ - *Abstract*: Massive Multiple Input-Multiple Output (mMIMO) technique has been considered an efficient standard to improve the transmission rate significantly for the following wireless communication systems, such as 5G and beyond. However, implementing this technology has been facing a critical issue of acquiring much channel state information. Primarily, this problem becomes more criticising in the integrated satellite and terrestrial networks (3GPP-Release 15) due to the countable high transmission delay. To deal with this challenging problem, the mMIMO-empowered non-coherent technique can be a promising solution. To our best knowledge, this paper is the first work considering employing the non-coherent mMIMO in satellite communication systems. This work aims to analyse the challenges and opportunities emerging with this integration. Moreover, we identified the issues in this conjunction. The preliminary results presented in this work show that the performance measured in bit error rate (BER) and the number of antennas are not far from that required for terrestrial links. Furthermore, thanks to mMIMO in conjunction with the non-coherent approach, we can work in a low signal-to-noise ratio (SNR) regime, which is an excellent advantage for satellite links. 102. **Non-Coherent Massive MIMO Integration in Satellite Communication** (2022) — Víctor Monzón Baeza, Vu Nguyen Ha, Jorge Querol, Symeon Chatzinotas. In *arXiv preprint arXiv:2209.09701*. | DOI: https://doi.org/10.1049/icp.2023.1386 | Open Access: https://hdl.handle.net/10993/52126 URL: https://jorge.querol.org/publication/monzon-2022-non/ - *Abstract*: Massive Multiple Input-Multiple Output (mMIMO) technique has been considered an efficient standard to improve the transmission rate significantly for the following wireless communication systems, such as 5G and beyond. However, implementing this technology has been facing a critical issue of acquiring much channel state information. Primarily, this problem becomes more criticising in the integrated satellite and terrestrial networks (3GPP-Release 15) due to the countable high transmission delay. To deal with this challenging problem, the mMIMO-empowered non-coherent technique can be a promising solution. To our best knowledge, this paper is the first work considering employing the non-coherent mMIMO in satellite communication systems. This work aims to analyse the challenges and opportunities emerging with this integration. Moreover, we identified the issues in this conjunction. The preliminary results presented in this work show that the performance measured in bit error rate (BER) and the number of antennas are not far from that required for terrestrial links. Furthermore, thanks to mMIMO in conjunction with the non-coherent approach, we can work in a low signal-to-noise ratio (SNR) regime, which is an excellent advantage for satellite links. 103. **Machine learning for radio resource management in multibeam GEO satellite systems** (2022) — Flor Ortíz, Lei Lei, Eva Lagunas, Ramón Martínez Rodríguez‐Osorio, Daniele Tarchi, Jorge Querol, Miguel A. Salas‐Natera, Symeon Chatzinotas. In *Electronics*. | DOI: https://doi.org/10.3390/electronics11070992 | Open Access: https://hdl.handle.net/10993/50865 URL: https://jorge.querol.org/publication/ortiz-2022-machine/ - *Abstract*: Satellite communications (SatComs) systems are facing a massive increase in traffic demand. However, this increase is not uniform across the service area due to the uneven distribution of users and changes in traffic demand diurnal. This problem is addressed by using flexible payload architectures, which allow payload resources to be flexibly allocated to meet the traffic demand of each beam. While optimization-based radio resource management (RRM) has shown significant performance gains, its intense computational complexity limits its practical implementation in real systems. In this paper, we discuss the architecture, implementation and applications of Machine Learning (ML) for resource management in multibeam GEO satellite systems. We mainly focus on two systems, one with power, bandwidth, and/or beamwidth flexibility, and the second with time flexibility, i.e., beam hopping. We analyze and compare different ML techniques that have been proposed for these architectures, emphasizing the use of Supervised Learning (SL) and Reinforcement Learning (RL). To this end, we define whether training should be conducted online or offline based on the characteristics and requirements of each proposed ML technique and discuss the most appropriate system architecture and the advantages and disadvantages of each approach. 104. **Hybridization of GNSS and 5G Measurements for Assured Positioning, Navigation and Timing** (2022) — Alejandro Gonzalez-Garrido, Jorge Querol, Symeon Chatzinotas. In *Proceedings of the 35th International Technical Meeting of the Satellite*. | Open Access: https://hdl.handle.net/10993/53185 URL: https://jorge.querol.org/publication/gonzalez-2022-hybridization/ - *Abstract*: Positioning, Navigation and Timing (PNT) services based on the Global Navigation Satellite System (GNSS) have a number of known drawbacks that makes them prone to suffer a disruption. These flaws can be exploited to disable this service in critical infrastructures. Therefore, the hybridization of GNSS and 5G measurements enabling Assured PNT (APNT) services is growing up and gaining attention by governmental bodies. 5G signals emitted by terrestrial networks and by Low Earth Orbit (LEO) satellites can complement GNSS, enhancing their reliability, security and accuracy. For example, the larger Signal-to-Noise Ratio (SNR) of a terrestrial system makes them more difficult to suffer a jamming attack as compared to GNSS signals. A joint data and positioning signal enhances the security and reliability of the APNT solution with, for example, the successful decoding of encrypted data, this could be used for system authentication. Moreover, a larger signal bandwidth increases the accuracy of the PNT solution. All of these benefits can be extracted from the 5G terrestrial and non-terrestrial networks that transmit the Positioning Reference Signal (PRS). The rationale for these benefits rely on the flexibility of this pilot signal in terms of bandwidth or symbols used for the APNT service. This paper aims to analyse how this flexibility can be optimized to achieve a specific level of accuracy, minimizing the resources used under certain constrains of bandwidth or latency. The results present the optimal parameters to design a 5G PRS waveform with a target scenario constrains. Then, we compare it with the GNSS service and how to benefit when using them in combination. Finally, the paper concludes with the future research lines proposing a joint communications and positioning system as a closed loop. In such scenario, the user achieved accuracy is sent back to the infrastructure, and using the dynamic PRS flexibility, the system increases or reduces the PRS resources in order to meet the user accuracy requirements. 105. **Differential phase compensation in over-the-air precoding test-bed for a multi-beam satellite** (2022) — Liz Martínez Marrero, Juan Carlos Merlano Duncán, Jorge Querol, Nicola Maturo, Jevgenij Krivochiza, Symeon Chatzinotas, Björn Ottersten. In *2022 IEEE Wireless Communications and Networking Conference (WCNC)*. | DOI: https://doi.org/10.1109/WCNC51071.2022.9771918 | Open Access: https://hdl.handle.net/10993/53080 URL: https://jorge.querol.org/publication/marrero-2022-differential/ - *Abstract*: This article presents a closed-loop differential phase compensation system for a precoding-enabled multibeam satellite forward link and its validation by live experiments on a GEO satellite scenario. The precoding operation avoids inter-beam interference and maximizes the spectrum efficiency by full frequency reuse as an alternative to the traditional two-color or four-color reuse methods proposed in the DVB-S2 standard. However, the satellite payload introduces differential phase and frequency impairments, which can degrade the precoding performance. This work describes the implementation of the differential phase and frequency tracking and compensation loop in an end-to-end testbed over a multibeam satellite system with independent local oscillators. The developed system performs end-to-end real-time communication over the satellite link, including channel measurements and precompensation. Results are validated by an over-the-air demonstration using two beams of the SES-14 multibeam satellite. Each beam is transmitted by independent transponders, which results in differential frequency and phase offsets due to the transponder undisciplined local oscillators. This phase offset makes it impossible to use precoding without the phase compensation loop. We prove that the implemented system can successfully track and compensate the differential phase and frequency to improve precoding performance. 106. **Architectures and synchronization techniques for distributed satellite systems: A survey** (2022) — Liz Martínez Marrero, Juan Carlos Merlano Duncán, Jorge Querol, Sumit Kumar, Jevgenij Krivochiza, Shree Krishna Sharma, Symeon Chatzinotas, Adriano Camps, Björn Ottersten. In *IEEE access*. | DOI: https://doi.org/10.1109/ACCESS.2022.3169499 | Open Access: https://hdl.handle.net/10993/53760 URL: https://jorge.querol.org/publication/marrero-2022-architectures/ - *Abstract*: Cohesive Distributed Satellite Systems (CDSSs) is a key enabling technology for the future of remote sensing and communication missions. However, they have to meet strict synchronization requirements before their use is generalized. When clock or local oscillator signals are generated locally at each of the distributed nodes, achieving exact synchronization in absolute phase, frequency, and time is a complex problem. In addition, satellite systems have significant resource constraints, especially for small satellites, which are envisioned to be part of the future CDSSs. Thus, the development of precise, robust, and resource-efficient synchronization techniques is essential for the advancement of future CDSSs. In this context, this survey aims to summarize and categorize the most relevant results on synchronization techniques for Distributed Satellite Systems (DSSs). First, some important architecture and system concepts are defined. Then, the synchronization methods reported in the literature are reviewed and categorized. This article also provides an extensive list of applications and examples of synchronization techniques for DSSs in addition to the most significant advances in other operations closely related to synchronization, such as inter-satellite ranging and relative position. The survey also provides a discussion on emerging data-driven synchronization techniques based on Machine Learning (ML). Finally, a compilation of current research activities and potential research topics is proposed, identifying problems and open challenges that can be useful for researchers in the field. 107. **5G-NTN GEO-based in-lab demonstrator using OpenAirInterface5G** (2022) — Sumit Kumar, Abdelrahman Abdalla, Oltjon Kodheli, Jorge Querol, Symeon Chatzinotas, Thomas Schlichter, Guido Casati, Thomas Heyn, Florian Volk, Sertac Kaya. In *11th Advanced Satellite Multimedia Conference*. | Open Access: https://hdl.handle.net/10993/53156 URL: https://jorge.querol.org/publication/kumar-20225-g/ - *Abstract*: This research contribution by Sumit Kumar, Abdelrahman Abdalla, Oltjon Kodheli, Jorge Querol et al. (2022), published in 11th Advanced Satellite Multimedia Conference, investigates "5G-NTN GEO-based in-lab demonstrator using OpenAirInterface5G" within the domains of 6G-NTN, Satellite Communications, AI & Neuromorphic SatCom. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 108. **5G space communications lab: Reaching new heights** (2022) — Oltjon Kodheli, Jorge Querol, Abdelrahman Astro, Sofia Coloma, Loveneesh Rana, Zhanna Bokal, Sumit Kumar, Carol Martinez Luna, Jan Thoemel, Juan Carlos Merlano Duncan, Miguel Angel Olivares Mendez, Symeon Chatzinotas, Bjorn Ottersten. In *2022 18th International Conference on Distributed Computing in Sensor*. | DOI: https://doi.org/10.1109/DCOSS54816.2022.00063 | Open Access: https://hdl.handle.net/10993/53019 URL: https://jorge.querol.org/publication/kodheli-20225-g/ - *Abstract*: The new era of space exploration demands a significant increase in the number of human and robotic missions, thus resulting in novel communication and service requirements. To satisfy such requirements, the fifth generation of mobile communication systems (5G), despite providing connectivity on Earth, has the potential to serve as a communication standard for space resource missions, particularly the ones targeting the Moon. In fact, 5G non-terrestrial networks (NTNs) are already in the standardization process and new techniques are being proposed in order to counteract the peculiarities of the non-terrestrial channel. However, going one step ahead and deploying constellations of satellites around the Earth or the Moon, requires first a detailed analysis and testing of the validity of the proposed techniques. Therefore, in this paper, we introduce the 5G Space Communications Lab, which has been developed with the purpose of simulating space-based 5G communications. The designed testbed proposed here increases the technology readiness level (TRL) of NTN-based 5G systems, demonstrating over a laboratory environment successful 5G communication via space links. 109. **Wireless and networking technologies for social distancing-indoor and outdoor** (2021) — Jorge Querol, Alejandro González, Vu Nguyen Ha, Sumit Kumar, Symeon Chatzinotas. In article-journal. | DOI: https://doi.org/10.1049/pbte104e_ch3 URL: https://jorge.querol.org/publication/querolwireless/ - *Abstract*: This chapter reviews the suitability of the most relevant wireless and networking communications technologies (e.g. GNSS, cellular, WiFi, Bluetooth and RFID) for the implementation of social distancing applications such as interpersonal distancing, real-time area monitoring, or geo-fencing. 110. **Solar-Aerodynamic Formation Flight for 5G Experiments** (2021) — Jan Thoemel, Jorge Querol, Zhanna Bokal, Juan Carlos Merlano Duncan, Mohammad Gholamian, Oltjon Kodheli, Sumit Kumar, Carol Martinez Luna, Nicola Maturo, Loveneesh Rana. In *Proceedings of the 12th European CubeSatSymposium*. | Open Access: https://hdl.handle.net/10993/50276 URL: https://jorge.querol.org/publication/thoemel-2021-solar/ - *Abstract*: This research contribution by Jan Thoemel, Jorge Querol, Zhanna Bokal, Juan Carlos Merlano Duncan et al. (2021), published in Proceedings of the 12th European CubeSatSymposium, investigates "Solar-Aerodynamic Formation Flight for 5G Experiments" within the domains of 6G-NTN. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 111. **Random access procedure over non-terrestrial networks: From theory to practice** (2021) — Oltjon Kodheli, Abdelrahman Astro, Jorge Querol, Mohammad Gholamian, Sumit Kumar, Nicola Maturo, Symeon Chatzinotas. In *IEEE Access*. | DOI: https://doi.org/10.1109/ACCESS.2021.3101291 | Open Access: https://hdl.handle.net/10993/50188 URL: https://jorge.querol.org/publication/kodheli-2021-random/ - *Abstract*: Non-terrestrial Networks (NTNs) have become an appealing concept over the last few years and they are foreseen as a cornerstone for the next generations of mobile communication systems. Despite opening up new market opportunities and use cases for the future, the novel impairments caused by the signal propagation over the NTN channel, compromises several procedures of the current cellular standards. One of the first and most important procedures impacted is the random access (RA) procedure, which is mainly utilized for achieving uplink synchronization among users in several standards, such as the fourth and fifth generation of mobile communication (4 & 5G) and narrowband internet of things (NB-IoT). In this work, we analyse the challenges imposed by the considerably increased delay in the communication link on the RA procedure and propose new solutions to overcome those challenges. A trade-off analysis of various solutions is provided taking into account also the already existing ones in the literature. In order to broaden the scope of applicability, we keep the analysis general targeting 4G, 5G and NB-IoT systems since the RA procedure is quasi-identical among these technologies. Last but not least, we go one step further and validate our techniques in an experimental setup, consisting of a user and a base station implemented in open air interface (OAI), and an NTN channel implemented in hardware that emulates the signal propagation delay. The laboratory test-bed built in this work, not only enables us to validate various solutions, but also plays a crucial role in identifying novel challenges not previously treated in the literature. Finally, an important key performance indicator (KPI) of the RA procedure over NTN is shown, which is the time that a single user requires to establish a connection with the base station. 112. **Parallel and distributed hybrid beamforming for multicell millimeter wave full duplex** (2021) — Chandan Kumar Sheemar, Symeon Chatzinotas, Dirk Slock, Eva Lagunas, Jorge Querol. In *arXiv preprint arXiv: 2112.02335*. | DOI: https://doi.org/10.48550/arXiv.2112.02335 | Open Access: https://hdl.handle.net/10993/62460 URL: https://jorge.querol.org/publication/sheemar-2021-parallel/ - *Abstract*: Full duplex (FD) is an auspicious wireless technology that holds the potential to double data rates through simultaneous transmission and reception. This paper proposes two innovative designs of hybrid beamforming (HYBF) for a multicell massive multiple-input-multiple-output (mMIMO) millimeter wave (mmWave) FD system. Initially, we introduce a novel centralized HYBF (C-HYBF) scheme, which employs the minorization-maximization (MM) method. However, while centralized beamforming designs offer superior performance, they suffer from high computational complexity, substantial communication overhead, and demand expensive computational resources. To surmount these challenges, we present a framework that facilitates per-link parallel and distributed HYBF (P$\&$D-HYBF) in the mmWave frequency band. This cooperative approach enables each base station (BS) to independently solve its local, low-complexity sub-problems in parallel, resulting in a substantial reduction in communication overhead and computational complexity. Simulation results demonstrate that P$\&$D-HYBF achieves comparable performance to C-HYBF, and with only a few radio-frequency (RF) chains, both designs surpass the capabilities of fully digital half duplex (HD) systems. 113. **End-to-end precoding validation over a live GEO satellite forward link** (2021) — Jevgenij Krivochiza, Juan Carlos Merlano Duncan, Jorge Querol, Nicola Maturo, Liz Martinez Marrero, Stefano Andrenacci, Jens Krause, Symeon Chatzinotas. In *IEEE Access*. | Open Access: https://hdl.handle.net/10993/46728 URL: https://jorge.querol.org/publication/krivochiza-2021-end/ - *Abstract*: In this paper we demonstrate end-to-end precoded multi-user multiple-input single-output (MU-MISO) communications over a live GEO satellite link. Precoded communications enable full frequency reuse (FFR) schemes in satellite communications (SATCOM) to achieve broader service availability and higher spectrum efficiency than with the conventional four-color (4CR) and two-color (2CR) reuse approaches. In this scope, we develop an over-the-air test-bed for end-to-end precoding validations. We use an actual multi-beam satellite to transmit and receive precoded signals using the DVB-S2X standard based gateway and user terminals. The developed system is capable of end-to-end real-time communications over the satellite link including channel measurements and precompensation. It is shown, that by successfully canceling inter-user interference in the actual satellite FFR link precoding brings gains in terms of enhanced SINR and increased system goodput. 114. **Centralized gateway concept for precoded multi-beam GEO satellite networks** (2021) — Steven Kisseleff, Eva Lagunas, Jevgenij Krivochiza, Jorge Querol, Nicola Maturo, Liz Martínez Marrero, Juan Carlos Merlano Duncán, Symeon Chatzinotas. In *2021 IEEE 94th Vehicular Technology Conference (VTC2021-Fall)*. | DOI: https://doi.org/10.1109/VTC2021-Fall52928.2021.9625524 | Open Access: https://hdl.handle.net/10993/48039 URL: https://jorge.querol.org/publication/kisseleff-2021-centralized/ - *Abstract*: Satellite Communications offer complementary benefits to terrestrial 5G/6G infrastructure, covering a wide range of use cases in need of ubiquitous coverage and reliability. However, to be as competitive as the terrestrial counterpart in terms of supplied throughput, satellite communications require a highly efficient use of the limited available spectrum. Linear precoding has demonstrated the ability to boost the spectral efficiency in the satellite domain, but raising a new issue: the bandwidth requirements of the feeder link. Deployment of several gateways, each of which precoding an independent cluster of beams causes performance degradation. Therefore, in this paper, we investigate the centralized gateway concept, where all digital baseband processes (including precoding) are implemented in a remote server connected via high speed fibers to the distributed remote gateways responsible for the downlink and uplink of the satellite radio frequency signals. In particular, we highlight the main technical challenges and provide a preliminary vision of potential solutions. 115. **A pre-correlation RFI mitigation algorithm for L-band interferometric radiometers** (2021) — Jorge Querol, A. Camps, A. Perez, R. Oliva, R. Onrubia, J. I. Ramirez-Martinez, A. Zurita, M. Suess, M. Martin-Neira. In *2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS*. | DOI: https://doi.org/10.1109/IGARSS47720.2021.9553195 URL: https://jorge.querol.org/publication/querol-2021-pre/ - *Abstract*: Radio Frequency Interference (RFI) is a major concern for both real and synthetic aperture radiometers. After the lessons learnt from SMOS, ESA is preparing the next generation of L-band interferometric radiometers with RFI mitigation integrated into the cross-correlators. This work presents a preliminary design and results of a pre-correlation RFI mitigation algorithm tailored for interferometric radiometers. The results show that the correlation error introduced by the RFI is reduced on average to the half, with peaks of 20 dB of mitigation. 116. **A design strategy for phase synchronization in Precoding-enabled DVB-S2X user terminals** (2021) — Liz Martinez Marrero, Juan Carlos Merlano Duncan, Jorge Querol, Symeon Chatzinotas, Adriano Camps, Bjorn Ottersten. In *ICC 2021-IEEE International Conference on Communications*. | DOI: https://doi.org/10.1109/ICC42927.2021.9500634 | Open Access: https://hdl.handle.net/10993/46321 URL: https://jorge.querol.org/publication/marrero-2021-design/ - *Abstract*: This paper address the design of a phase tracking block for the DVB-S2X user terminals in a satellite precoding system. The spectral characteristics of the phase noise introduced by the oscillator, the channel, and the thermal noise at the receiver are taken into account. Using the expected phase noise mask, the optimal parameters for a second-order PLL intended to track channel variations from the pilots are calculated. To validate the results a Simulink model was implemented considering the characteristics of the hardware prototype. The performance of the design was evaluated in terms of the accuracy and stability for the frame structure of superframe Format 2, as described in Annex E of DVB-S2X. 117. **A cubesat-ready phase synchronization digital payload for coherent distributed remote sensing missions** (2021) — Jorge Querol, J. C. Merlano-Duncan, L. Martinez-Marrero, J. Krivochiza, S. Kumar, N Maturo, A. Camps, S. Chatzinotas, B. Ottersten. In *2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS*. | DOI: https://doi.org/10.1109/IGARSS47720.2021.9554042 | Open Access: https://hdl.handle.net/10993/48050 URL: https://jorge.querol.org/publication/querol-2021-cubesat/ - *Abstract*: Distributed antenna arrays, fractionated payloads and cooperative platforms can provide unprecedented performance in the next generation of spaceborne communications and remote sensing systems. Remote phase synchronization of physically separated oscillators is the first step towards a coherent operation of distributed systems. This work shows the preliminary results of a TDD remote phase synchronization algorithm with a master-follower architecture. Herein, we describe the implementation and validation of the proposed algorithm. The implementation has been conducted in a Cubesat-ready software defined radio and validated at the end-to-end satellite communications testbed available at the University of Luxembourg. 118. **5G-SpaceLab** (2021) — Jorge Querol, Abdelrahman Abdalla, Zhanna Bokal, Juan Carlos Merlano Duncan, Mohammad Gholamian, Oltjon Kodheli, Jevgenij Krivochiza, Sumit Kumar, Carol Martinez Luna, Nicola Maturo. In *2021 Space Resources Week*. | Open Access: https://hdl.handle.net/10993/47772 URL: https://jorge.querol.org/publication/querol-20215-g/ - *Abstract*: This research contribution by Jorge Querol, Abdelrahman Abdalla, Zhanna Bokal, Juan Carlos Merlano Duncan et al. (2021), published in 2021 Space Resources Week, investigates "5G-SpaceLab" within the domains of 6G-NTN. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 119. **5G-NTN Prototyping and Experimentation Results** (2021) — Sumit Kumar, Jorge Querol, Symeon Chatzinotas, Marwan Hammouda, Thomas Heyn, Thomas Schlichter, Paulo Marques, Luis Pereira, Roberto Magueta, Florian Völk. In article-journal. URL: https://jorge.querol.org/publication/kumar-5-g/ - *Abstract*: This research contribution by Sumit Kumar, Jorge Querol, Symeon Chatzinotas, Marwan Hammouda et al. (2021), published in peer-reviewed journal, investigates "5G-NTN Prototyping and Experimentation Results" within the domains of 6G-NTN. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 120. **Technology developments for an advanced l-band radiometer mission** (2020) — Manuel Martin-Neira, Martin Suess, Nikos Karafolas, Petri Piironen, Francois Deborgies, Albert Catalan, Roger Vilaseca, Josée Montero, Montserrat Puertolas, Diego Outumuro, Ignasi Corbella, Israel Duran, Nuria Duffo, Roberto Materni, Teresa Mengual, Miguel Angel Piqueras, Ana Olea, Andres Solana, Joséep Closa, Albert Zurita, Juan Ignacio Ramirez, Olav Breinbjerg, Jeppe Majlund Bjorstorp, Kyriakos Kaslis, Steen S. Kristensen, Roger Oliva, Raul Onrubia, Adriano Camps, Jorge Querol. In *IGARSS 2020-2020 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS39084.2020.9324378 URL: https://jorge.querol.org/publication/martin-2020-technology/ - *Abstract*: ESA's Soil Moisture and Ocean Salinity (SMOS) mission was launched 2 Nov 2009 and, to date, is still in good health, providing valuable L-band observations of the Earth surface [1]. A number of products are obtained from these, including thin sea ice [2], frost/thaw soils [3], high winds [4], ocean surface wind [5] and Sun brightness temperature [6], besides the main mission measurements of soil moisture and sea surface salinity [7] [8]. This paper deals with the description and early results of some technology activities conducted by ESA applying the lessons learnt by SMOS and in preparation of an advanced L-band radiometer mission. 121. **System modeling and design aspects of next generation high throughput satellites** (2020) — Shree Krishna Sharma, Jorge Querol Borras, Nicola Maturo, Symeon Chatzinotas, Bjorn Ottersten. In *IEEE Communications Letters*. | DOI: https://doi.org/10.1109/LCOMM.2020.3036593 | Open Access: https://hdl.handle.net/10993/45240 URL: https://jorge.querol.org/publication/sharma-2020-system/ - *Abstract*: As compared to terrestrial systems, the design of Satellite Communication (SatCom) systems requires a different approach due to differences in terms of wave propagation, operating frequency, antenna structures, interfering sources, limitations of onboard processing, power limitations and transceiver impairments. In this regard, this letter aims to identify and discuss important modeling and design aspects of the next generation High Throughput Satellite (HTS) systems. First, communication models of HTSs including the ones for multibeam and multicarrier satellites, multiple antenna techniques, and for SatCom payloads and antennas are highlighted and discussed. Subsequently, various design aspects of SatCom transceivers including impairments related to the transceiver, payload and channel, and traffic-based coverage adaptation are presented. Finally, some open topics are identified and discussed. 122. **System Modelling and Design Aspects of Next Generation High Throughput Satellites** (2020) — Shree Krishna Sharma, Jorge Querol, Nicola Maturo, Symeon Chatzinotas, Björn Ottersten. In *arXiv e-prints*. | DOI: https://doi.org/10.48550/arXiv.2011.09333 | Open Access: https://hdl.handle.net/10993/45240 URL: https://jorge.querol.org/publication/krishna-2020-system/ - *Abstract*: As compared to terrestrial systems, the design of Satellite Communication (SatCom) systems requires a different approach due to differences in terms of wave propagation, operating frequency, antenna structures, interfering sources, limitations of onboard processing, power limitations and transceiver impairments. In this regard, this letter aims to identify and discuss important modeling and design aspects of the next generation High Throughput Satellite (HTS) systems. First, communication models of HTSs including the ones for multibeam and multicarrier satellites, multiple antenna techniques, and for SatCom payloads and antennas are highlighted and discussed. Subsequently, various design aspects of SatCom transceivers including impairments related to the transceiver, payload and channel, and traffic-based coverage adaptation are presented. Finally, some open topics are identified and discussed. 123. **Satellite communications in the new space era: A survey and future challenges** (2020) — Oltjon Kodheli, Eva Lagunas, Nicola Maturo, Shree Krishna Sharma, Bhavani Shankar, Jesus Fabian Mendoza Montoya, Juan Carlos Merlano Duncan, Danilo Spano, Symeon Chatzinotas, Steven Kisseleff, Jorge Querol. In *IEEE Communications Surveys & Tutorials*. | Open Access: https://hdl.handle.net/10993/45772 URL: https://jorge.querol.org/publication/kodheli-2020-satellite/ - *Abstract*: Satellite communications (SatComs) have recently entered a period of renewed interest motivated by technological advances and nurtured through private investment and ventures. The present survey aims at capturing the state of the art in SatComs, while highlighting the most promising open research topics. Firstly, the main innovation drivers are motivated, such as new constellation types, on-board processing capabilities, non-terrestrial networks and space-based data collection/processing. Secondly, the most promising applications are described, i.e., 5G integration, space communications, Earth observation, aeronautical and maritime tracking and communication. Subsequently, an in-depth literature review is provided across five axes: i) system aspects, ii) air interface, iii) medium access, iv) networking, v) testbeds & prototyping. Finally, a number of future challenges and the respective open research topics are described. 124. **SDR implementation of a testbed for synchronization of coherent distributed remote sensing systems** (2020) — J. C. Merlano-Duncan, Jorge Querol, L. Martinez-Marrero, J. Krivochiza, A. Camps, S. Chatzinotas, B. Ottersten. In *IGARSS 2020-2020 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS39084.2020.9324220 | Open Access: https://hdl.handle.net/10993/46215 URL: https://jorge.querol.org/publication/merlano-2020-sdr/ - *Abstract*: Remote Sensing from distributed platforms has become attractive for the community in the last years. Phase, frequency, and time synchronization are a crucial requirement for many such applications as multi-static remote sensing and also for distributed beamforming for communications. The literature on the field is extensive, and in some cases, the requirements an complexity of the proposed synchronization solution may surpass the ones set by the application itself. Moreover, the synchronization solution becomes even more challenging when the nodes are flying or hovering on aerial or space platforms. In this work, we discuss the synchronization considerations for the implementation of distributed remote sensing applications. The general framework considered is based on a distributed collection of autonomous nodes that synchronize their clocks with a common reference using inter-satellite links. For this purpose, we implement a synchronization link between two nodes operating in a full-duplex fashion. The experimental testbed uses commercially available SDR platforms to emulate two satellites, two targets, and the communication channel. The proposal is evaluated considering phase and frequency errors for different system parameters. 125. **Radio-frequency interference location, detection and classification using deep neural networks** (2020) — A. Perez, Jorge Querol, H. Park, A. Camps. In *IGARSS 2020-2020 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS39084.2020.9324532 | Open Access: https://hdl.handle.net/10993/41379 URL: https://jorge.querol.org/publication/perez-2020-radio/ - *Abstract*: Global Navigation Satellite System (GNSS) signals are used in Earth Observation for Radio Occultation and Reflectometry. The increasing effects of Radio-Frequency Interferences (RFI) on the performance of these receivers and navigation have suddenly sparked serious concerns due to their proliferation. Detection and mitigation of RFI heavily relies on the nature and location of the interfering sources. In some cases, null-steering or shielding can be used to mitigate RFI effects. In this work, a system to detect and locate RFI sources is presented, including signal classification and recording for countermeasure-related decision-making. 126. **L-band vegetation optical depth estimation using transmitted GNSS signals: Application to GNSS-reflectometry and positioning** (2020) — Adriano Camps, Alberto Alonso-Arroyo, Hyuk Park, Raul Onrubia, Daniel Pascual, Jorge Querol. In *Remote sensing*. | DOI: https://doi.org/10.3390/rs12152352 URL: https://jorge.querol.org/publication/camps-2020-band/ - *Abstract*: At L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C/N0) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C/N0 and NDVI data, obtaining R2 coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50°. Data were also fit to a simple τ-ω model to estimate a single scattering albedo parameter (ω) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (ω(θe)), at elevation angles smaller than ~67°, the ω(θe) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning. 127. **Implementation of a testbed for GNSS-R payload performance evaluation** (2020) — Adrián Pérez-Portero, Joan Francesc Muñoz-Martín, Jorge Querol, Hyuk Park, Adriano Camps. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/JSTARS.2020.2997717 | Open Access: https://hdl.handle.net/10993/46215 URL: https://jorge.querol.org/publication/perez-2020-implementation/ - *Abstract*: The functional performance of space-borne instruments must be validated on ground before and after satellite integration. The effects of radio-frequency interference are also becoming more important, even in protected bands for earth observation. In this article, a GNSS and GNSS-R signal simulator is developed as part of a testbed of GNSS receivers and GNSS-R payloads' performance in high dynamics, and to study the effects of RFI in the GNSS-R observables. This article describes the different concepts and key enabling techniques that have been developed to support this project. 128. **A remote carrier synchronization technique for coherent distributed remote sensing systems** (2020) — Juan Carlos Merlano Duncán, Liz Martínez Marrero, Jorge Querol, Sumit Kumar, Adriano Camps, Symeon Chatzinotas, Björn Ottersten. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/JSTARS.2020.3046776 | Open Access: https://hdl.handle.net/10993/45428 URL: https://jorge.querol.org/publication/merlano-2020-remote/ - *Abstract*: Phase, frequency, and time synchronization are crucial requirements for many applications, such as multistatic remote sensing and communication systems. Moreover, the synchronization solution becomes even more challenging when the nodes are orbiting or flying on airborne or spaceborne platforms. This article compares the available technologies used for the synchronization and coordination of nodes in distributed remote sensing applications. Additionally, this article proposes a general system model and identifies preliminary guidelines and critical elements for implementing the synchronization mechanisms exploiting the intersatellite communication link. The distributed phase synchronization loop introduced in this work deals with the self-interference in a full-duplex point to point scenario by transmitting two carriers at each node. All carriers appear with different frequency offsets around a central frequency, called the application central-frequency or the beamforming frequency. This article includes a detailed analysis of the proposed algorithm and the required simulations to verify its performance for different phase noise, additive white Gaussian noise, and Doppler shift scenarios. 129. **Real-time Radio Frequency Interference Detection and Mitigation with the Front-End GNSS Interference eXcisor (FENIX)** (2019) — Jorge Querol, Adrián Pérez-Portero, Joan Francesc Muñoz-Martín, Adriano Camps. In *RFI 2019 - Coexisting with Radio Frequency Interference*. | DOI: https://doi.org/10.1109/RFI48793.2019.9111819 | Open Access: https://hdl.handle.net/10993/42797 URL: https://jorge.querol.org/publication/querol-2019-real/ - *Abstract*: This paper presents the real-time hardware architecture and experimental evaluation of the Front-End GNSS Interference eXcisor (FENIX), demonstrating standalone pre-correlation time-frequency excision of continuous-wave, chirp, and pulsed jamming signals across civilian GNSS bands. 130. **Architectures and synchronization techniques for coherent distributed remote sensing systems** (2019) — Juan Carlos Merlano-Duncan, Jorge Querol, Adriano Camps, Symeon Chatzinotas, Björn Ottersten. In *IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS.2019.8898444 | Open Access: https://hdl.handle.net/10993/40788 URL: https://jorge.querol.org/publication/merlano-2019-architectures/ - *Abstract*: Coherent Distributed Remote Sensing Systems require strict time, frequency, and phase synchronization across distributed satellite nodes. This paper analyzes distributed architectures and wireless inter-satellite synchronization techniques suitable for coherent multistatic SAR, interferometric radiometry, and GNSS reflectometry missions. 131. **The global navigation satellite systems reflectometry (GNSS-R) microwave interferometric reflectometer: Hardware, calibration, and validation experiments** (2019) — Raul Onrubia, Daniel Pascual, Jorge Querol, Hyuk Park, Adriano Camps. In *Sensors*. | DOI: https://doi.org/10.3390/s19051019 URL: https://jorge.querol.org/publication/onrubia-2019-global/ - *Abstract*: This manuscript describes the Microwave Interferometric Reflectometer (MIR) instrument, a multi-beam dual-band GNSS-Reflectometer with beam-steering capabilities built to assess the performance of a PAssive Reflectrometry and Interferometry System-In Orbit Demonstrator (PARIS-IoD) like instrument and to compare the performance of different GNSS-R techniques and signals. The instrument is capable of tracking up to 4 different GNSS satellites, two at L1/E1 band, and two at L5/E5 band. The calibration procedure of the up- and down-looking arrays is presented, the calibration performance is evaluated, and the results of the validation experiments carried out before the field experiments are shown in this paper. 132. **On the new architecture and capabilities of the front-end GNSS interference excisor (FENIX)** (2019) — Adrián Pérez, Adriano Camps, Jorge Querol. In *IGARSS 2019-2019 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/igarss.2019.8900263 URL: https://jorge.querol.org/publication/perez-2019-new/ - *Abstract*: The number of applications based on Global Navigation Satellite Systems (GNSS) has been increasing in the last years. With its proliferation, Radio-Frequency Interference (RFI) has become one of the most concerning topics on GNSS-based devices for navigation, positioning and timing, but also for Earth Observation purposes such as GNSS-Reflectometry and Radio Occultations due to the corruption of the received signal and the corresponding geophysical measurements. The Front-End GNSS Interference eXcisor (FENIX) mitigates the problem of RFI by providing a plug and play solution to excise interferences out of virtually any system. The new version of FENIX is also capable of operating with large signal bandwidths (~50 MHz) and dual-frequency applications. This paper shows the performance of the system for commercial GNSS receivers and GNSS-reflectometry applications. A discussion of the impact of the new architecture on its future capabilities is presented as well. 133. **Hardware precoding demonstration in multibeam UHTS communications under realistic payload characteristics** (2019) — Juan Duncan, Jorge Querol, Nicola Maturo, Jevgenij Krivochiza, Danilo Spano, Norshahida Saba, Liz Marrero, Symeon Chatzinotas, Björn Ottersten. In *Advances in Communications Satellite Systems. Proceedings of the 37th*. | Open Access: https://hdl.handle.net/10993/41695 URL: https://jorge.querol.org/publication/duncan-2019-hardware/ - *Abstract*: In this chapter, we present a new hardware test-bed to demonstrate closed-loop precoded communications for interference mitigation in multibeam ultrahigh throughput satellite systems under realistic payload and channel impairments. We build the test-bed to demonstrate a real-time channel aided precoded transmission under realistic conditions such as the power constraints and satellite-payload nonlinearities. We develop a scalable architecture of an SDR platform with the DVB-S2X piloting. The SDR platform consists of two parts: analog-to-digital (ADC) and digital-to-analog (DAC) converters preceded by radio frequency (RF) front end and field-programmable gate array (FPGA) backend. The former introduces realistic impairments in the transmission chain such as carrier frequency and phase misalignments, quantization noise of multichannel ADC and DAC, and nonlinearities of RF components. It allows evaluating the performance of the precoded transmission in a more realistic environment rather than using only numerical simulations. We benchmark the performance of the communication standard in realistic channel scenarios, evaluate received signal SNR, and measure the actual channel throughput using LDPC codes. 134. **Effects of differential oscillator phase noise in precoding performance** (2019) — L. Martinez Marrero, J.C. Merlano Duncan, Jorge Querol, S. Chatzinotas, A.J. Camps Carmona, B. Ottersten. In *Advances in Communications Satellite Systems. Proceedings of the 37th*. | DOI: https://doi.org/10.1049/cp.2019.1261 URL: https://jorge.querol.org/publication/marrero-2019-effects/ - *Abstract*: This research contribution by L. Martinez Marrero, J.C. Merlano Duncan, Jorge Querol, S. Chatzinotas et al. (2019), published in Advances in Communications Satellite Systems. Proceedings of the 37th, investigates "Effects of differential oscillator phase noise in precoding performance" within the domains of Beamforming & MIMO. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 135. **Demonstrator of precoding technique for a multi-beams satellite system** (2019) — Nicola Maturo, Juan Carlos Merlano Duncan, Jevgenij Krivochiza, Jorge Querol, Danilo Spano, Symeon Chatzinotas, Björn Ottersten. In *2019 8th International Workshop on Tracking, Telemetry and Command*. | DOI: https://doi.org/10.1109/TTC.2019.8895466 | Open Access: https://hdl.handle.net/10993/41151 URL: https://jorge.querol.org/publication/maturo-2019-demonstrator/ - *Abstract*: In this document, we present a real-time demonstrator of precoding technique, to be used to enable full frequency reuse in the forward link of future multi-beam satellite systems. To this aim, our demonstrator will implement all the functionalities required to correctly exploit the achievable gain coming from the usage of precoding. In particular, the main functionality to be included on the User Terminal (UT) side is the proper collection of the estimated Channel State Information (CSI). On the Gateway (GW), a computationally-efficient calculation of the precoding matrix and application of the resulting precoder to the vectors of symbol streams, have to been developed. Using this demonstrator we are able to prove the feasibility of precoding implementation in satellite communications relying on the superframe framing structure defined in Annex E of the DVB-S2X standard. 136. **A review of RFI mitigation techniques in microwave radiometry** (2019) — Jorge Querol, Adrián Pérez-Portero, Adriano Camps. In *Remote Sensing*. | DOI: https://doi.org/10.3390/RS11243042 | Open Access: https://hdl.handle.net/10993/41375 URL: https://jorge.querol.org/publication/querol-2019-review/ - *Abstract*: Radio frequency interference (RFI) is a well-known problem in microwave radiometry (MWR). Any undesired signal overlapping the MWR protected frequency bands introduces a bias in the measurements, which can corrupt the retrieved geophysical parameters. This paper presents a literature review of RFI detection and mitigation techniques for microwave radiometry from space. The reviewed techniques are divided between real aperture and aperture synthesis. A discussion and assessment of the application of RFI mitigation techniques is presented for each type of radiometer. 137. **Radio frequency interference detection and mitigation techniques for navigation and Earth observation** (2018) — Jorge Querol. In *PhD Thesis, Universitat Politècnica de Catalunya (UPC-BarcelonaTech)*. | DOI: https://doi.org/10.5821/dissertation-2117-125028 | Open Access: https://hdl.handle.net/10993/41379 URL: https://jorge.querol.org/publication/querol-2018-radio/ - *Abstract*: This PhD thesis is devoted to the design, implementation, and experimental validation of innovative Radio-Frequency Interference (RFI) detection, localization, and mitigation countermeasures in the fields of Microwave Radiometry (MWR), Global Navigation Satellite Systems (GNSS), and GNSS-Reflectometry (GNSS-R). It completes the development of the MERITXELL multi-frequency radiometer, introduces the Multiresolution Fourier Transform (MFT) mitigation algorithm, proposes the Generalized Spectral Separation Coefficient (GSSC) metric for GNSS-R under interference, and presents the patented FENIX real-time pre-correlation anti-jamming architecture (US Patent US9596610B1), demonstrating up to 30 dB of jamming resilience across GPS L1 C/A, GPS L2C, and Galileo E1OS signals. Awarded Best PhD Thesis 2018 by the IEEE Geoscience and Remote Sensing Society (GRSS) Spanish Chapter. 138. **‘Ionospheric scintillation impact on GNSS-R altimetry** (2018) — A Camps, H Park, E Lancheros, R Onrubia, D Pascual, Jorge Querol. In *GNSS+ R, Ann Arbor, MI, USA, Tech. Rep*. URL: https://jorge.querol.org/publication/camps-2018-ionospheric/ - *Abstract*: This research contribution by A Camps, H Park, E Lancheros, R Onrubia et al. (2018), published in GNSS+ R, Ann Arbor, MI, USA, Tech. Rep, investigates "‘Ionospheric scintillation impact on GNSS-R altimetry" within the domains of JCAS & Earth Observation, GNSS & Positioning, Quantum & Optical Space Links. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 139. **Wind direction signatures in GNSS-R observables from space** (2018) — Dongliang Guan, Hyuk Park, Adriano Camps, Yong Wang, Raul Onrubia, Jorge Querol, Daniel Pascual. In *Remote Sensing*. | DOI: https://doi.org/10.3390/rs10020198 URL: https://jorge.querol.org/publication/guan-2018-wind/ - *Abstract*: Wind speed and direction are important essential climate variables (ECVs). GNSS-R is an emerging remote sensing technique that can be potentially used to retrieve wind speed from space. However, few studies have addressed the wind direction retrieval from spaceborne GNSS-R observables, namely the Delay Doppler map (DDM). In this study, the feasibility of retrieving wind direction from the synthetic DDMs is analyzed. First, the simulation tool P2EPS is used to generate the DDMs under different geometry configurations, wind speed, and wind direction. Then, DDM changes caused by the wind direction are investigated, and two metrics are proposed to retrieve the wind direction from the DDM shape changes. The influence on wind direction retrieval of the wind speed, receiver’s elevation, and azimuth is further discussed. Finally, the sensitivity of DDM changes to noise is investigated, as well as the impact of noise on these two metrics. 140. **Spaceborne GNSS-R end-to-end simulator: Topography and vegetation effects** (2018) — H. Park, A. Camps, D. Pascual, Jorge Querol, R. Onrubia. In *IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS.2018.8517790 URL: https://jorge.querol.org/publication/park-2018-spaceborne/ - *Abstract*: As the TDS-1 and CYGNSS spaceborne GNSS-R missions progress, a large number of Delay-Doppler Maps (DDM) is being collected, from the land scattered as well as from the ocean. Based on those data, the feasibility study on the retrieval of land geophysical parameters such as soil moisture and vegetation is being studied. This work presents the E2E simulator that generates the synthesized DDM reflected over land. For the efficient development, the existing simulator for ocean scattering has been upgraded to accommodate the specific functionalities for land scattering: topography, surface roughness, vegetation effects, in addition to surface soil moisture, obviously. The developed end-to-end (E2E) simulator is used to conceive the retrieval algorithms and assess their performance. In this work, the upgraded items are described and illustrated with some simulation results. 141. **RFI analysis and mitigation in airborne GNSS-R campaign** (2018) — Jorge Querol, R. Onrubia, D. Pascual, J. Castellvi-Esturi, H. Park, A. Camps. In *IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS.2018.8518827 URL: https://jorge.querol.org/publication/querol-2018-rfi/ - *Abstract*: Radio-Frequency Interference (RFI) is one of the most concerning topics in Global Navigation Satellite Systems (GNSS) and GNSS - Reflectometry (GNSS-R) because any undesired signal present at the antenna can corrupt the received signal and the eventual geophysical measurements. The purpose of this paper is two-fold. First, an RFI analysis is performed to the raw data obtained from an airborne dual-band GNSS reflectometer. Finally, the Front-End GNSS Interference eXcisor (FENIX) mitigation algorithm is applied to the raw data, and then the Signal-to-Noise Ratio (SNR) improvement at the Delay-Doppler Map (DDM) is obtained. From the analysis of one of the datasets, two RFI signals were detected and characterized. Moreover, FENIX output signal was revealed to be much cleaner than before. The mean SNR improvement with coherent DDMs of 1 ms is 0.72 dB, whereas the SNR improvement increases to 1.49 dB when considering 50 incoherent averages. This improvement represents a reduction in the geophysical parameter estimation uncertainty. 142. **Preliminary altimetry results of the MALYGNSS instrument in the HUMIT project** (2018) — R. Onrubia, D. Pascual, Jorge Querol, J. Castellvi-Esturi, J. Corbera, H. Park, A. Camps. In *IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS.2018.8518636 URL: https://jorge.querol.org/publication/onrubia-2018-preliminary/ - *Abstract*: In order to provide high resolution soil moisture maps, the Institut Cartografic i Geológic de Catalunya (ICGC) in colab-oration with Universitat Politecnica de Catalunya are planing to deploy the3Cat-3 picosatellite, which aims to estimate soil moisture from space using Global Navigation Satellite Systems - Reflectometry (GNSS-R) and to downscale it using data fusion with a multi-spectral camera. As a proof of concept, a field campaign is being carried out in Lleida, Catalunya. MALYGNSS is a GNSS reflectometer flying as an opportunity sensor that will validate the main reflectometer of the project: the CORTO instrument. 143. **Generic simulator for conical scanning microwave radiometers** (2018) — H. Park, A. Camps, Jorge Querol, K. Szczepankiewicz, C. De Negueruela, W. Oryszczak, L. Soto, R. Kedzierawski, F. E. Aleman Roda. In *2018 IEEE 15th Specialist Meeting on Microwave Radiometry and Remote*. | DOI: https://doi.org/10.1109/MICRORAD.2018.8430699 URL: https://jorge.querol.org/publication/park-2018-generic/ - *Abstract*: This work describes a software tool developed for ESA within the project BIBLOS-2 (BuIlding BLOcks for earth observation mission performance simulator) to model typical conical scanning microwave radiometers in a generic Earth Observation mission. It consists of functional modules: Geometry, Scene Generator, Instrument, and Level 1 data generation modules. This structure follows the architecture for generic Earth Observation mission simulator study, ARCHEO-E2E (ARCHitecture of Earth Observation). The improvement in the BIBLOS-2 Passive Microwave is developing the Radio Frequency Interferences (RFI) generation and mitigation functionality. The developed simulation modules will be provided soon via the BIBLOS web page (https://gmv-biblos.gmv.com/). In this paper, the functions of the BIBLOS-2 passive microwave are described module by module, including the RFI generation/mitigation examples. 144. **Determination of sea correlation time at L-Band with airborne reflected new GNSS signals** (2018) — D. Pascual, R. Onrubia, Jorge Querol, J. Castellvi-Esturi, H. Park, A. Camps. In *IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS.2018.8518552 URL: https://jorge.querol.org/publication/pascual-2018-determination/ - *Abstract*: The maximum coherent integration time of GNSS reflected (GNSS-R) signals over sea depends on the sea state, as well as on the geometry formed by the receiver, the GNSS satellite and the reflection point. In this paper, real data obtained with a dedicated airborne instrument named MALYGNSS (Multi-band Airborne L-Band reflectometrY with GNSS) is used to acquire GPS L1 C/A and L2C, and Galileo E1OS signals. The direct signals are used as a reference to detect any phase shift due to data bits changes and the presence of a residual Doppler frequency. These phase transitions are removed in the reflected signals, and coherent correlations of different lengths are performed in order to study sea correlation time. 145. **Antena Bi-banda con conformación de dos haces simultáneos para sistemas GNSS-R** (2018) — Raúl Onrubia Ibáñez, Daniel Pascual Biosca, Jorge Querol, Adriano Joséé Camps Carmona. In *XXXIII Simposium Nacional de la Unión Cientı́fica Internacional de*. URL: https://jorge.querol.org/publication/onrubia-2018-antena/ - *Abstract*: This research contribution by Raúl Onrubia Ibáñez, Daniel Pascual Biosca, Jorge Querol, Adriano Joséé Camps Carmona (2018), published in XXXIII Simposium Nacional de la Unión Cientı́fica Internacional de, investigates "Antena Bi-banda con conformación de dos haces simultáneos para sistemas GNSS-R" within the domains of JCAS & Earth Observation, GNSS & Positioning. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 146. **An anti-jamming system for GNSS timing applications** (2018) — Jorge Querol, Adriano Camps, Esteban Garbin Manfredini, Ricardo Piriz. In *2018 European Frequency and Time Forum (EFTF)*. | DOI: https://doi.org/10.1109/EFTF.2018.8409021 URL: https://jorge.querol.org/publication/querol-2018-anti/ - *Abstract*: Radio-Frequency Interference (RFI) and jamming are increasing problems for timing applications based on Global Navigation Satellite Systems (GNSS). FENIX-lite is a real-time pre-correlation anti-jamming system designed to provide increased resilience against RFI/jamming in critical GNSS-enabled applications. This work aims to evaluate the combined performance of FENIX-lite and a timing setup composed by two GNSS disciplined oscillators named DOWR. The results show that FENIX provides an anti-jamming resilience of 10-30 dB, at the expense of introducing a small bias and an additional jitter of 2-4 ns. 147. **3CAT-3/MOTS, an experimental nanosatellite for multispectral and GNSS-R earth observation: airborne optical and GNSS-R campaign** (2018) — Jordi Castellvi-Esturi, Adriano Camps, Jordi Corbera, Raul Onrubia, Ramon Alamús, Daniel Pascual, Jorge Querol, Hyuk Park. In *IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/igarss.2018.8518216 URL: https://jorge.querol.org/publication/castellvi-20183-cat/ - *Abstract*: The3Cat-3/MOTS mission is a joint initiative between the Institut Cartogràfic i Geològic de Catalunya (ICGC) and the Universitat Politècnica de Catalunya-BarcelonaTech (UPC) to foster new and innovative technologies on Earth Observation (EO) based on the data fusion of Global Navigation Satellite Systems Reflectometry (GNSS-R) and optical payloads on a 6U CubeSat platform. The final objective of the mission is to provide soil moisture mapping through the GNSS-R payload and improve its resolution by data fusion with the multi-spectral optical data acquired. This technique has been successfully applied to SMOS, but never performed from a 6U CubeSat carrying both payloads. An airborne optical and GNSS-R field experiment has been carried out to test/develop the algorithm and to analyze the results both separately (GNSS-R + optical data) and as a soil moisture product, once performed the data fusion. 148. **A radio-frequency interference detector for GNSS navigation and GNSS-reflectometry applications** (2017) — Jorge Querol, Raul Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps. In *2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2017.8127965 URL: https://jorge.querol.org/publication/querol-2017-radio/ - *Abstract*: This paper presents a real-time Radio-Frequency Interference (RFI) detection and monitoring system designed for Global Navigation Satellite Systems (GNSS) navigation and GNSS-Reflectometry (GNSS-R) receivers operating at L-band, evaluating detection sensitivity against continuous-wave, swept-chirp, and pulsed interference sources. 149. **System and method for detecting and eliminating radio frequency interferences in real time** (2017) — Jorge Querol, Adriano Joséé Camps Carmona. In manuscript. URL: https://jorge.querol.org/publication/querol-2017-system/ - *Abstract*: This research contribution by Jorge Querol, Adriano Joséé Camps Carmona (2017), published in international conference proceedings, investigates "System and method for detecting and eliminating radio frequency interferences in real time" within the domains of RFI Mitigation & GNSS Security. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech. 150. **SNR and standard deviation of cGNSS-R and iGNSS-R scatterometric measurements** (2017) — Alberto Alonso-Arroyo, Jorge Querol, Carlos Lopez-Martinez, Valery Zavorotny, Hyuk Park, Daniel Pascual, Raul Onrubia, Adriano Camps. In *Sensors*. | DOI: https://doi.org/10.3390/s17010183 URL: https://jorge.querol.org/publication/alonso-2017-snr/ - *Abstract*: This work addresses the accuracy of the Global Navigation Satellite Systems (GNSS)-Reflectometry (GNSS-R) scatterometric measurements considering the presence of both coherent and incoherent scattered components, for both conventional GNSS-R (cGNSS-R) and interferometric GNSS-R (iGNSS-R) techniques. The coherent component is present for some type of surfaces, and it has been neglected until now because it vanishes for the sea surface scattering case. Taking into account the presence of both scattering components, the estimated Signal-to-Noise Ratio (SNR) for both techniques is computed based on the detectability criterion, as it is done in conventional GNSS applications. The non-coherent averaging operation is considered from a general point of view, taking into account that thermal noise contributions can be reduced by an extra factor of 0.88 dB when using partially overlapped or partially correlated samples. After the SNRs are derived, the received waveform's peak variability is computed, which determines the system's capability to measure geophysical parameters. This theoretical derivations are applied to the United Kingdom (UK) TechDemoSat-1 (UK TDS-1) and to the future GNSS REflectometry, Radio Occultation and Scatterometry on board the International Space Station (ISS) (GEROS-ISS) scenarios, in order to estimate the expected scatterometric performance of both missions. 151. **Real-time Pre-correlation Anti-jamming System for Civilian GNSS Receivers** (2017) — Jorge Querol, Adriano Camps. In *Proceedings of the 30th International Technical Meeting of The Satellite*. | DOI: https://doi.org/10.33012/2017.15304 URL: https://jorge.querol.org/publication/querol-2017-real/ - *Abstract*: Global Navigation Satellite Systems (GNSS) have become a key technology that enables numerous location and navigation applications, thanks to the 24/7 worldwide availability of their signals, and the positioning accuracy that can be reached with them. However, GNSS have also some weaknesses, and the most relevant is that their signals reach the Earth’s surface with very low power. This makes them quite vulnerable to the effect of Radio-Frequency Interference (RFI), and particularly to intentional jamming, which degrades, or even disrupts, the performance of the receivers. This problem is particularly threatening for those critical GNSS-enabled applications that trust on the integrity and continuity of GNSS signals, whose reliability may be committed. Such liability/security-critical civilian applications include autonomous aerial/terrestrial navigation, automatic rail signaling, geo-localized toll/insurance payments, or network synchronization among others. Moreover, RFI is also troublesome for derived GNSS applications such as GNSS-Reflectometry (GNSS-R) where GNSS signals are used as signals of opportunity in a multi-static radar configuration for Earth observation purposes. A number of mitigation solutions have been proposed to increase the continuity of GNSS signals in the presence of jamming signals. Regarding the structure of a GNSS system, the mitigation process can be performed at different stages: antenna, front-end, pre-correlation, post-correlation, or measurement. Common antenna solutions can provide spatiotemporal selectivity, which can reach interference rejection ration higher than 40 dB, but this is only achieved in static scenarios. On the contrary, pre-correlation techniques work at signal level, between antenna and GNSS correlators, providing interference selectivity in time, frequency, statistical, or other sub-space signal domains, which can mitigate jamming signals regardless the scenario dynamics. Moreover, pre-correlation techniques usually have a high computational burden in order to achieve high performance with interference rejection ratios higher than 30 dB. However, last generation Field Programmable Gate Arrays (FPGA) can overcome this drawback, and they even enable real-time pre-correlation anti-jamming solutions. The Front-End GNSS Interference eXcisor (FENIX) is a GNSS anti-jamming technology based on the patented combination of statistical interference detection, and a multiresolution time-frequency blanking algorithm for jamming mitigation in DSSS-based multi-constellation GNSS receivers [1]. The main goal of FENIX is to increase the C/N0 in the presence of interference signals, thus improving the continuity of GNSS services. Moreover, the mitigation algorithm has been designed to be DSSS-based multi-constellation, frequency independent (i.e. it works at L1 and L2, L5…), and it is capable of mitigating almost all kinds of jamming signals. A general description of the major building blocks of FENIX was first presented in [2]. This work aims at showing the implementation and first results of a real-time L1/L2 GPS/Galileo lite version of FENIX (FENIX-lite) tested using commercial jammers and GNSS receivers. The FENIX-lite demonstrator has been implemented using a two Software Defined Radio (SDR) model USRP B200mini, the first covers the GPS L1 C/A and Galileo E1 OS services, whereas the second does the same with the GPS L2C signal. The SDR front-ends are tuned to the L1 and L2 bands, and the FENIX interference detection and mitigation algorithm is running in real-time in both FPGA. The FENIX algorithm detects the interference signal using a statistical domain analysis based on normality tests, while the samples containing most part of interference power signal are excised in the time-frequency space computed using the Multiresolution Fourier Transform (MFT). The use of the MFT allows to mitigate almost of kinds of jamming signals since it maximized the projection of the interference signal in the transformed domain as demonstrated in [3]. In order to evaluate the improvement in the continuity of the GNSS signals, the degradation of the SNR with and without the FENIX-lite is compared using jammers at different bands and commercial GNSS receivers. [1] J. Querol, and A. Camps, “System and method for detecting and eliminating radio frequency interferences in real time,” U.S. Patent Application 15 222 036, issued date July 28, 2016. [2] J. Querol, E. M. Julian, R. Onrubia, A. Alonso-Arroyo, D. Pascual and A. Camps, “Preliminary results of FENIX: Front-End GNSS Interference eXcisor,” 2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Beijing, 2016, pp. 5627-5630. [3] J. Querol; R. Onrubia; A. Alonso-Arroyo; D. Pascual; H. Park; A. Camps, “Performance Assessment of Time-Frequency RFI Mitigation Techniques in Microwave Radiometry,” in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, in press. 152. **Performance assessment of time--frequency RFI mitigation techniques in microwave radiometry** (2017) — Jorge Querol, R. Onrubia, A. Alonso-Arroyo, Daniel Pascual, Hyuk Park, Adriano Camps. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/JSTARS.2017.2654541 URL: https://jorge.querol.org/publication/querol-2017-performance/ - *Abstract*: Radio-frequency interference (RFI) signals are a well-known threat for microwave radiometry (MWR) applications. In order to alleviate this problem, different approaches for RFI detection and mitigation are currently under development. Since RFI signals are man made, they tend to have their power more concentrated in the time-frequency (TF) space as compared to naturally emitted noise. The aim of this paper is to perform an assessment of different TF RFI mitigation techniques in terms of probability of detection, resolution loss (RL), and mitigation performance. In this assessment, six different kinds of RFI signals have been considered: a glitch, a burst of pulses, a wide-band chirp, a narrow-band chirp, a continuous wave, and a wide-band modulation. The results show that the best performance occurs when the transform basis has a similar shape as compared to the RFI signal. For the best case performance, the maximum residual RFI temperature is 14.8 K, and the worst RL is 8.4%. Moreover, the multiresolution Fourier transform technique appears as a good tradeoff solution among all other techniques since it can mitigate all RFI signals under evaluation with a maximum residual RFI temperature of 21 K, and a worst RL of 26.3%. Although the obtained results are still far from an acceptable bias <; 1 K for MWR applications, there is still work to do in a combined test using the information gathered simultaneously by all mitigation techniques, which could improve the overall performance of RFI mitigation. 153. **MERITXELL: the Multifrequency Experimental Radiometer with Interference Tracking for Experiments over Land and Littoral—instrument description, calibration and performance** (2017) — Jorge Querol, J. M. Tarongíi, Giuseppe Forte, Joséé Luís Eguia Gómez, Adriano Camps. In *Sensors*. | DOI: https://doi.org/10.3390/S17051081 URL: https://jorge.querol.org/publication/querol-2017-meritxell/ - *Abstract*: MERITXELL is a ground-based multisensor instrument that includes a multiband dual-polarization radiometer, a GNSS reflectometer, and several optical sensors. Its main goals are twofold: to test data fusion techniques, and to develop Radio-Frequency Interference (RFI) detection, localization and mitigation techniques. The former is necessary to retrieve complementary data useful to develop geophysical models with improved accuracy, whereas the latter aims at solving one of the most important problems of microwave radiometry. This paper describes the hardware design, the instrument control architecture, the calibration of the radiometer, and several captures of RFI signals taken with MERITXELL in urban environment. The multiband radiometer has a dual linear polarization total-power radiometer topology, and it covers the L-, S-, C-, X-, K-, Ka-, and W-band. Its back-end stage is based on a spectrum analyzer structure which allows to perform real-time signal processing, while the rest of the sensors are controlled by a host computer where the off-line processing takes place. The calibration of the radiometer is performed using the hot-cold load procedure, together with the tipping curves technique in the case of the five upper frequency bands. Finally, some captures of RFI signals are shown for most of the radiometric bands under analysis, which evidence the problem of RFI in microwave radiometry, and the limitations they impose in external calibration. 154. **Calibration of GNSS-R receivers with PRN signal injection: Methodology and validation with the microwave interferometric reflectometer (MIR)** (2017) — D. Pascual, R. Onrubia, Jorge Querol, H. Park, A. Camps. In *2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2017.8128131 URL: https://jorge.querol.org/publication/pascual-2017-calibration/ - *Abstract*: The demonstration of the feasibility of navigation signals signals for remote sensing has lead to a significant increase of new GNSS-R instruments in the recent years. Despite of the type instrument, the observables are based on the cross-correlations of the received GNSS signals. Most of these instruments combine the signals received by multiple chains, in such a way that they need a proper calibration. This work proposes a calibration procedure for GNSS-R instruments by using a calibration signal with similar statistics to the GNSS signals. The method is tested and validated with the Microwave Interferometric Reflectometer (MIR) instrument, which contains 152 chains. The test results will be presented at the conference. 155. **Beamformer characterization of the MIR instrument: The microwave interferometric reflectometer** (2017) — R. Onrubia, D. Pascual, Jorge Querol, H. Park, A. Camps. In *2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2017.8128132 URL: https://jorge.querol.org/publication/onrubia-2017-beamformer/ - *Abstract*: Global Navigation Satellite Systems - Reflectometry (GNSS-R) has opened promising results for remote sensing applications. The broadcast of new signals with wider bandwidth provides an opportunity to increase the performance of GNSS reflectometry applications. The Microwave Interferometric Reflectometer (MIR) is an instrument being developed to compare different GNSS-R techniques, namely the conventional and interferometric ones, and assess the capabilities of these new signals and bands of the GPS and Galileo systems. This work describes the tests to validate the beamforming system. 156. **A generic level 1 simulator for spaceborne GNSS-R missions and application to GEROS-ISS ocean reflectometry** (2017) — Hyuk Park, Adriano Camps, Daniel Pascual, Yujin Kang, R. Onrubia, Jorge Querol, A. Alonso-Arroyo. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/JSTARS.2017.2720625 URL: https://jorge.querol.org/publication/park-2017-generic/ - *Abstract*: In the past decade Global Navigation Satellites System Reflectometry (GNSS-R) has emerged as a new technique for earth remote sensing for various applications, such as ocean altimetry and sea state monitoring. After the success of the GNSS-R demonstrator payloads aboard the UK-DMC or TDS-1 satellites; at present, there are several missions planned to carry GNSS reflectometers. The GNSS rEflectometry, Radio Occultation, and Scatterometry onboard International Space Station (GEROS-ISS) is an innovative ISS experiment exploiting GNSS-R technique to measure key parameters of ocean, land, and ice surfaces. For GEROSISS mission, the European Space Agency (ESA) supported the study of GNSS-R assessment of requirements and consolidation of retrieval algorithms (GARCA). For this, it was required to accurately simulate the GEROS-ISS measurements including the whole range of parameters affecting the observation conditions and the instrument, which is called GEROS-SIM. To meet these requirements, the PAU/PARIS end-to-end performance simulator (P2 EPS) previously developed by UPC BarcelonaTech was used as the baseline building blocks for the level 1 (L1) processor of GEROS-SIM. P2EPS is a flexible tool, and is capable of systematically simulating the GNSS-R observations for spaceborne GNSS-R missions. Thanks to the completeness and flexibility, the instrument-to-L1 data module of GEROS-SIM could be implemented by proper modification and update of P2EPS. The developed GEROS-SIM was verified and validated in the GARCA study as comparing to the TDS-1 measurements. This paper presents the design, implementation, and results of the GEROS-SIM L1 module in a generic way to be applied to GNSS-R instruments. 157. **SNR degradation in GNSS-R measurements under the effects of radio-frequency interference** (2016) — Jorge Querol, A. Alonso-Arroyo, R. Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/JSTARS.2016.2597438 URL: https://jorge.querol.org/publication/querol-2016-snr/ - *Abstract*: Radio-frequency interference (RFI) is a serious threat for systems working with low power signals such as those coming from the global navigation satellite systems (GNSS). The spectral separation coefficient (SSC) is the standard figure of merit to evaluate the signal-to-noise ratio (SNR) degradation due to the RFI. However, an in-depth assessment in the field of GNSS-Reflectometry (GNSS-R) has not been performed yet, and particularly, about which is the influence of the RFI on the so-called delay-Doppler map (DDM). This paper develops a model that evaluates the contribution of intra-/inter-GNSS and external RFI effects to the degradation of the SNR in the DDM for both conventional and interferometric GNSS-R techniques. Moreover, a generalized SSC is defined to account for the effects of nonstationary RFI signals. The results show that highly directive antennas are necessary to avoid interference from other GNSS satellites, whereas mitigation techniques are essential to keep GNSS-R instruments working under external RFI degradation. 158. **Preliminary results of FENIX: front-end GNSS interference eXcisor** (2016) — Jorge Querol, E. M. Julian, R. Onrubia, A. Alonso-Arroyo, D. Pascual, A. Camps. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2016.7730470 URL: https://jorge.querol.org/publication/querol-2016-preliminary/ - *Abstract*: The number of applications based on Global Navigation Satellite Systems (GNSS) has been increasing in last years. In the passive remote sensing field, GNSS-Reflectometry (GNSS-R) systems have been revealed as cost-effective solutions to retrieve a number of geophysical parameters. However, GNSS-based devices are prone to suffer from Radio-Frequency Interference (RFI) effects due to the extreme low power of involved signals. This paper shows the preliminary results of the Front-End GNSS Interference eXcisor (FENIX), a system designed to mitigate the RFI problem in GNSS-based systems. FENIX is composed by two stages: the RF stage and the SP stage. The former conditions the signal from the antenna, throw the SP stage, and to the receiver; and the latter excises the RFI from the GNSS signal combining thresholding with the Multiresolution Fourier Transform (MFT). Preliminary results show that FENIX can mitigate up to 30 dB a chirp RFI signal generated from commercial jammers. 159. **On the correlation between GNSS-R reflectivity and L-band microwave radiometry** (2016) — Alberto Alonso-Arroyo, Adriano Camps, Alessandra Monerris, Christoph Rudiger, Jeffrey P. Walker, Raul Onrubia, Jorge Querol, Hyuk Park, Daniel Pascual. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/jstars.2016.2588281 URL: https://jorge.querol.org/publication/alonso-2016-correlation/ - *Abstract*: This work compares microwave radiometry and global navigation satellite systems-reflectometry (GNSS-R) observations using data gathered from airborne flights conducted for three different soil moisture conditions. Two different regions are analyzed, a crops region and a grassland region. For the crops region, the correlation with the I/2 (first Stokes parameter divided by two) was between 0.74 and 0.8 for large incidence angle reflectivity data (30°-50°), while it was between 0.51 and 0.61 for the grassland region and the same incidence angle conditions. For the crops region, the correlation with the I/2 was between 0.64 and 0.69 for lower incidence angle reflectivity data (<;30°), while it was between 0.41 and 0.6 for the grassland region. This indicates that for large incidence angles the coherent scattering mechanism is dominant, while the lower incidence angles are more affected by incoherent scattering. Also a relationship between the reflectivity and the polarization index (PI) is observed. The PI has been used to remove surface roughness effects, but due to its dependence on the incidence angle only the large incidence angle observations were useful. The difference in ground resolution between microwave radiometry and GNSS-R and their strong correlation suggests that they might be combined to improve the spatial resolution of microwave radiometry measurements in terms of brightness temperature and consequently soil moisture retrievals. 160. **Improvement of PAU/PARIS end-to-end performance simulator (P 2 EPS): Land scattering including topography** (2016) — Hyuk Park, Adriano Camps, Daniel Pascual, Alberto Alonso-Arroyo, Jorge Querol, Raul Onrubia. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2016.7730464 URL: https://jorge.querol.org/publication/park-2016-improvement/ - *Abstract*: This work presents an improvement of the P2EPS end-to-end simulator to assess the performances of Global Navigation Satellite System Reflectometry (GNSS-R) space missions over land. Beyond the single specular reflection model, topography effects are included. In order to avoid the computational burden of facet approach based on the bi-static radar model, the Phong reflection model is employed. By calculating the delay, Doppler frequency, and relative intensity of scattered points, the topography effects can be accounted for as a sort of impulse response in the delay, and Doppler domains to be convolved with the Woodward Ambiguity function. 161. **Impact of multi-path by ISS structure on GEROS-ISS measured waveforms** (2016) — Hyuk Park, Adriano Camps, Ivan Sekulic, J. M. Rius, Daniel Pascual, Alberto Alonso-Arroyo, Jorge Querol, Raul Onrubia. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2016.7730463 URL: https://jorge.querol.org/publication/park-2016-impact/ - *Abstract*: The GNSS rEflectometry, Radio Occultation and Scatterometry onboard the International Space Station (GEROS-ISS) experiment consists of the installation of a GNSS reflectometry (GNSS-R) instrument on the International Space Station (ISS). Due to the complex structure of ISS, the GEROS-ISS instrument suffers from multipath effects. The collected signals are not only from received directly, but also after multiple reflections in the ISS structure. This work analyzes the multipath effect of the GEROS-ISS instrument based on the ISS structure. Using the ray tracing simulation, all rays reaching the instrument after one or two reflections are computed, as well as the corresponding additional delays. This information, together with the direction of arrival to the antenna arrays (up and down-looking), and the co- and cross-polar antenna patterns is used to assess the impact of multipath on the waveforms are demonstrated. 162. **First Delay Doppler Maps obtained with the Microwave Inteferometric Reflectometer (MIR)** (2016) — D. Pascual, R. Onrubia, Jorge Querol, A. Alonso-Arroyo, H. Park, A. Camps. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2016.7729514 URL: https://jorge.querol.org/publication/pascual-2016-first/ - *Abstract*: This work presents the first Delay Doppler Maps (DDMs) obtained with the Microwave Interferometric Reflectometer (MIR) airborne instrument. MIR is a GNSS Reflectometer (GNSS-R) which uses the conventional (cGNSS-R) and interferometric (iGNSS-R) techniques for ocean and land observation. It computes real-time sample-to-sample complex DDMs with averaging and alignment, of up to 4 simultaneous GPS/Galileo satellites at the L1/E1, and L5/E5a bands. Satellites are tracked with high directivity antennas with beam steering. The MIR instrument is designed to validate and compare both GNSS-R techniques with the new available signals, with special focus in the GEROS-ISS payload, and to contribute to the development of geophysical retrieval algorithms. 163. **DME/TACAN impact analysis on GNSS reflectometry** (2016) — R. Onrubia, Jorge Querol, Daniel Pascual, A. Alonso-Arroyo, Hyuk Park, Adriano Camps. In *IEEE Journal of Selected Topics in Applied Earth Observations and Remote*. | DOI: https://doi.org/10.1109/JSTARS.2016.2556745 URL: https://jorge.querol.org/publication/onrubia-2016-dme/ - *Abstract*: Global navigation satellite system reflectometry (GNSS-R) is becoming a widely accepted technique for remote sensing. The interferometric technique (iGNSS-R) correlates the direct signal received from a satellite and the same signal reflected on the Earth's surface, whereas the conventional technique (cGNSS-R) correlates the reflected signal with a locally generated replica of the transmitted code. As GNSS signals are received below the noise level, this technique is extremely sensitive to radio frequency interference. The distance measurement equipment, and the TACtical air navigation systems are two radio navigation systems that transmit in the GPS L5, and Galileo E5 bands with powers up to 3.5 kW. This work studies in depth the impact of these systems on iGNSS-R, and cGNSS-R instruments. This study is then applied to a hypothetical reflectometer that will be placed in the international space station: The GEROS experiment. It is shown that the received power in space will be strong enough to degrade the system's performance by increasing the noise floor, but the sea altimetry precision will still be accurate enough for scientific studies. 164. **Crosstalk statistics and impact in interferometric GNSS-R** (2016) — Daniel Pascual, Hyuk Park, R. Onrubia, A. Alonso-Arroyo, Jorge Querol, Adriano Camps. In *IEEE journal of selected topics in applied earth observations and remote*. | DOI: https://doi.org/10.1109/JSTARS.2016.2551981 URL: https://jorge.querol.org/publication/pascual-2016-crosstalk/ - *Abstract*: This paper presents a statistical analysis of the crosstalk phenomenon in interferometric Global Navigation Satellite Systems Reflectometry (iGNSS-R). Crosstalk occurs when the Delay-Doppler Map (DDM) of a tracked satellite overlaps others from undesired satellites. This study is performed for ground-based and airborne receivers and for a receiver onboard the International Space Station (ISS) such as the upcoming GNSS Reflectometry, Radio Occultation and Scatterometry onboard ISS experiment. Its impact on ocean altimetry retrievals is analyzed for different antenna arrays. Results show that for elevation angles higher than 60°, crosstalk can be almost permanent from ground, up to 61% from airborne receivers at 2-km height, and up to ~10% at the ISS. Crosstalk can only be mitigated using highly directive antennas with narrow beamwidths. Crosstalk impact using a seven-element hexagonal array still induces large errors on ground, but reduces to centimeter level on airborne receivers, and is negligible from the ISS. 165. **Comparison of real-time time-frequency RFI mitigation techniques in microwave radiometry** (2016) — Jorge Querol, R. Onrubia, D. Pascual, A. Alonso-Arroyo, H. Park, A. Camps. In *2016 14th Specialist Meeting on Microwave Radiometry and Remote Sensing*. | DOI: https://doi.org/10.1109/MICRORAD.2016.7530506 URL: https://jorge.querol.org/publication/querol-2016-comparison/ - *Abstract*: Radio-Frequency Interference (RFI) is a well-known problem for Microwave Radiometers (MWR). A number of RFI mitigation techniques have been studied to deal with RFI from the receiver's side. In this study, a comparison in terms of performance among several real-time time-frequency RFI mitigation techniques is presented. Time-frequency techniques are of high importance because the vast majority of RFI signals are well-localized in the time-frequency space. The five techniques compared under study are: Pulse Blanking (PB), Frequency Blanking (FB), Spectrogram Blanking (SB), Wavelet Denoising (WD), and Multiresolution Fourier Transform (MFT). Results show that the best performance depends on the particular type of RFI, and occurs when the transform basis is similar to the RFI, that is, the projection on that particular basis is maximized. However, there is not a single technique that is effective for all RFI signals, and future approaches may be based on a combination of several techniques. 166. **Can we measure vegetation water content and vegetation opacity at L-band with a single GPS receiver?** (2016) — A. Alonso-Arroyo, Jorge Querol, A. Camps, R. Onrubia, H. Park, D. Pascual. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/igarss.2016.7729512 URL: https://jorge.querol.org/publication/alonso-2016-can/ - *Abstract*: This work shows a technique to estimate the vegetation opacity and infer the vegetation water content using a single GPS receiver located under the vegetation layer being analyzed. It is based on the measurement of the received signal power when the GPS satellite is at the zenith, and when the GPS satellite is with an elevation of 30 degrees. Assuming a horizontally stratified vegetation layer, the attenuation on the GPS signal due to vegetation doubles at 30° elevation angle compared to the zenith. This attenuation is directly related to the vegetation opacity. Then, the vegetation opacity is related to the vegetation water content by a linear parameter. Initial results relating the measured GPS signal power to canopy parameters obtained from hemispheric photos are shown. 167. **Assessment of DME/TACAN RFI mitigation techniques in GNSS-R** (2016) — R. Onrubia, Jorge Querol, D. Pascual, H. Park, A. Alonso-Arroyo, A. Camps. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2016.7730255 URL: https://jorge.querol.org/publication/onrubia-2016-assessment/ - *Abstract*: Global Navigation Satellite Systems Reflectometry (GNSSR) is now being recognized as a powerfull tool for remote sensing. With the addition of new frequency bands and codes, it is possible to increase the resolution and accuracy of the measurements. GPS L5 and Galileo E5 bands are becoming popular because of the open codes, with wider bandwidths than the L1 band ones. However, these bands are shared with two radio navigation systems (DME and TACAN) that transmit with high powers and might interfere them. The use of mitigation techniques may affect the power of the received signal, which will affect the GNSS-R observables. This work presents several the mitigation techniques, and evaluates the performance and impact of the selected ones for ESA's GEROS experiment onboard the International Space Station. 168. **Altimetric performance of the GEROS experiment at the ISS** (2016) — A. Camps, H. Park, R. Onrubia, D. Pascual, Jorge Querol, A. Alonso-Arroyo, J. Benito, A. Andres-Beivide, S. Moreno, X. Ballesteros, M. Segarra, R. Vilaseca, A. Rius, M. Martin-Neira. In *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/igarss.2016.7730468 URL: https://jorge.querol.org/publication/camps-2016-altimetric/ - *Abstract*: The GNSS rEflectometry, Radio Occultation and Scatterometry onboard the International Space Station (GEROS-ISS) is an innovative experiment for climate research, proposed in 2011 within a call of the European Space Agency (ESA) for installation at the ISS. This international proposal was the only one selected for further studies by ESA out of ~25 submitted ones. In this work, an updated assessment of the instrument performance for the near-nadir altimetry (GNSS-R) mode and scatterometry is assessed, including the effect of the inter-modulation signals, and the expected degradation due to presence of radio-frequency interference coming from DME/TACAN systems. These results correspond to the study lead by Airbus Defence and Space-Spain, one of the two parallel Phase A studies conducted by ESA. 169. **Two dedicated soil moisture experiments using the scatterometric properties of GNSS-reflectometry** (2015) — A. Alonso-Arroyo, S. Torrecilla, Jorge Querol, A. Camps, D. Pascual, H. Park, R. Onrubia. In *2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/igarss.2015.7326682 URL: https://jorge.querol.org/publication/alonso-2015-two/ - *Abstract*: This work presents two field campaigns performed between December 2014 and June 2015 in order to better understand the behavior of Global Navigation Satellite Systems (GNSS) reflected signals over land. The instruments used in both field campaigns are briefly introduced. One of them is focused on circular polarization, whereas the other is focused on linear polarization (horizontal and vertical). In one field experiment there is evidence of multipath due to the antenna performance. A method to mitigate it is proposed in this work. Finally, some preliminary soil moisture estimations using vertical polarization are shown. 170. **First results of a GNSS-R experiment from a stratospheric balloon over boreal forests** (2015) — Hugo Carreno-Luengo, Adriano Camps, Jorge Querol, Giuseppe Forte. In *IEEE Transactions on Geoscience and Remote Sensing*. | DOI: https://doi.org/10.1109/tgrs.2015.2504242 URL: https://jorge.querol.org/publication/carreno-2015-first/ - *Abstract*: The empirical results of a global navigation satellite systems reflectometry (GNSS-R) experiment onboard the Balloon EXperiments for University Students (BEXUS) 17 stratospheric balloon performed north of Sweden over boreal forests show that the power of the reflected signals is nearly independent of the platform height for a high coherent integration time Tc= 20 ms. This experimental evidence shows a strong coherent component in the forward scattered signal, as compared with the incoherent component, that allows to be tracked. The bistatic coherent reflectivity is also evaluated as a function of the elevation angle, showing a decrease of ~6 dB when the elevation angle increases from 35° to 70°. The received power presents a clearly multimodal behavior, which also suggests that the coherent scattering component may be taking place in different forest elements, i.e., soil, canopy, and through multiple reflections canopy-soil and soil-trunk. This experiment has provided the first GNSS-R data set over boreal forests. The evaluation of these results can be useful for the feasibility study of this technique to perform biomass monitoring that is a key factor to analyze the carbon cycle. 171. **Assessment of back-end RFI mitigation techniques in passive remote sensing** (2015) — Jorge Querol, A. Alonso-Arroyo, R. Onrubia, D. Pascual, A. Camps. In *2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2015.7326890 URL: https://jorge.querol.org/publication/querol-2015-assessment/ - *Abstract*: Radio-Frequency Interference (RFI) is a growing problem specially for those systems that work with low power signals such as passive remote sensing instruments. Consequently, RFI mitigation techniques are currently under development. This works aims at evaluating back-end mitigation algorithms in terms of their probability of detection and mitigation performance. Results show that Wavelet Denoising (WD), and Multiresolution Fourier Transform (MFT) are the best techniques in most scenarios, specially for GNSS-based instruments. 172. **Advances in the MIR instrument: Integration, control subsystem and analysis of the flight dynamics for beamsteering purposes** (2015) — R. Onrubia, L. Garrucho, D. Pascual, H. Park, Jorge Querol, A. Alonso-Arroyo, A. Camps. In *2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*. | DOI: https://doi.org/10.1109/IGARSS.2015.7326895 URL: https://jorge.querol.org/publication/onrubia-2015-advances/ - *Abstract*: The MIR (Microwave Interferometric Reflectometer) is a new dual frequency Global Navigation Satellite Systems Reflectometry (GNSS-R) instrument that implements conventional and interferometric reflectometry, both with GPS and Galileo signals. This paper presents the instrument development progress, mainly in the control part, where a methodology to determine how much the platform attitude will affect the beam steering and a satellite selection algorithm have been developed. 173. **Study of RFI signals in protected GNSS bands generated by common electronic devices: Effects on GNSS-R measurements** (2014) — Jorge Querol, G. F. Forte, A. Camps. In *2014 IEEE Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/IGARSS.2014.6947375 URL: https://jorge.querol.org/publication/querol-2014-study/ - *Abstract*: RFI (Radio Frequency Interference) signals are a threat for GNSS-R (Global Navigation Satellite Systems - Reflectometry) due to the very low power of the navigation signals. Interference signals coming from computers or high-speed buses may affect GNSS-R measurements introducing a bias or even corrupting them completely. These RFI may be in-band or near-band and can desensitize GNSS and GNSS-R receivers. A number of techniques are currently under development to mitigate the effect of RFI signals. 174. **Review of GNSS-R instruments and tools developed at the Universitat Politecnica de Catalunya-Barcelona tech** (2014) — A. Camps, J. F. Marchan-Hernandez, X. Bosch-Lluis, N. Rodriguez-Alvarez, I. Ramos-Perez, E. Valencia, J. M. Tarongíi, H. Park, H. Carreno-Luengo, A. Alonso-Arroyo, D. Pascual, R. Onrubia, G. Forte, Jorge Querol. In *2014 IEEE Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/igarss.2014.6947318 URL: https://jorge.querol.org/publication/camps-2014-review/ - *Abstract*: Reflectometry using Global Navigation Satellite System's signals of opportunity (GNSS-R) was originally conceived in the early 90s for mesoscale altimetry, and since then, many studies have shown its applicability to other remote sensing applications. In 2002, the Remote Sensing Lab at the Universitat Politècnica de Catalunya started working in Global Navigation Satellite Reflectometry (GNSS-R) to perform a more accurate correction of the sea state when retrieving sea surface salinity from L-band microwave radiometer data (e.g. SMOS). During these 12 years, the lab has developed ground-based, airborne, balloon, and spaceborne GNSS-R payloads for a number of different applications. This paper provides an overview of the families of instruments, and the design choices made. 175. **A stratospheric balloon GNSS-R experiment: The 3 Cat-2 project in DLR/SNSB BEXUS** (2014) — H. Carreno-Luengo, A. Camps, Jorge Querol, G. Forte, R. Onrubia, R. Diez. In *2014 IEEE Geoscience and Remote Sensing Symposium*. | DOI: https://doi.org/10.1109/igarss.2014.6947268 URL: https://jorge.querol.org/publication/carreno-2014-stratospheric/ - *Abstract*: Universitat Politècnica de Catalunya (UPC) - BarcelonaTech Remote Sensing Laboratory focus on the development of breakthrough concepts. The3Cat-2 mission is on the synergy of GNSS reflectometry and the CubeSat concept. Scientifically valuable mission data will improve our understanding on the Earth's environment. In particular, ocean currents need further investigation because of the spatio-temporal evolution of the mesoscale phenomena. The spacecraft development work includes two stratospheric flights in the frame of the REXUS/BEXUS programme coordinated by the European Space Agency (ESA). Coherent and incoherent scattering of Earth-reflected GNSS signals as sensed by the P(Y) & C/A ReflectOmeter (PYCARO) payload will be evaluated using the main state-of-the art Global Navigation Satellite Systems Reflectometry (GNSS-R) methodologies. Future spaceborne activities could take advantage of it, including the GNSS REflectometry, Radio Occultation and Scatterometry on-board International Space Station (GEROS-ISS) experiment. 176. **Real-time RFI detection and mitigation system for microwave radiometers** (2013) — Giuseppe F. Forte, Jorge Querol, Adriano Camps, Merce Vall-llossera. In *IEEE transactions on geoscience and remote sensing*. | DOI: https://doi.org/10.1109/tgrs.2013.2267595 URL: https://jorge.querol.org/publication/forte-2013-real/ - *Abstract*: Microwave radiometers are very sensitive passive sensors that measure the power of the thermal noise within a determined bandwidth. Therefore, any other signal present in the band modifies the value of the measured power, and the corresponding estimated antenna temperature, from which the geophysical parameters are retrieved. Due to the high sensitivity and accuracy required for these instruments, radio frequency interference (RFI) is becoming more and more a serious problem. On one hand, ground-based or global RFI surveys are helping to understand the occurrence and types of RFI sources. If RFI does not necessarily affect the whole bandwidth, or it is not present during the whole integration time, the application of either frequency blanking, time blanking or signal spectrogram techniques can be applied. However, it would be desirable to apply techniques to estimate the RFI signal so that it can be subtracted from the received signal itself so that some useful measurements are still possible. Such a real-time system is currently being developed for RFI detection and mitigation. This work focuses however in the description and performance of a wavelet-based RFI-mitigation technique implemented in a FPGA hardware back-end. The interfering signal is estimated by using the powerful denoising capabilities of the wavelet transform, and it is then subtracted from the total received signal to obtain a RFI-mitigated noise signal. 177. **Implementation of Radio-Frequency Interference Detection and Mitigation Algorithms for Communications and Navigation** (2013) — Jorge Querol. In *Master Thesis, Universitat Politècnica de Catalunya (UPC-BarcelonaTech)*. URL: https://jorge.querol.org/publication/querol-2013-implementation/ - *Abstract*: Radio-Frequency Interference (RFI) signals are undesired signals that degrade or disrupt the performance of wireless communications and satellite navigation receivers. This Master Thesis presents the design, real-time FPGA hardware implementation, and experimental validation of digital signal processing algorithms for the detection and mitigation of continuous-wave, chirp, and pulsed radio-frequency interference in Global Navigation Satellite Systems (GNSS) and passive microwave remote sensing receivers. 178. **Digital back-end for RFI detection and mitigation in earth observation** (2013) — G.F. Forte, Jorge Querol, H. Park, A. Camps. In *2013 IEEE International Geoscience and Remote Sensing Symposium-IGARSS*. | DOI: https://doi.org/10.1109/igarss.2013.6723177 URL: https://jorge.querol.org/publication/forte-2013-digital/ - *Abstract*: A powerful real time Radio-frequency interference (RFI) mitigation back-end system is presented in this work. The interfering signals are estimated by using the wavelet transform to utilize its effective denoising capability. The estimated RFI signals are then subtracted from the total received signal, and ultimately the RFI-mitigated signal is obtained. Here, the hardware implementation and the system tests are demonstrated, showing sinusoid, chirp, and PRN interference mitigation under different Interference to Noise Ratios (INRs). 179. **MCU Controlled DC-DC Buck/Boost Converter for Supercapacitors** (2012) — Jorge Querol. In thesis. URL: https://jorge.querol.org/publication/querol-2012-mcu/ - *Abstract*: This work is focused on DC to DC conversion, what is a crucial function to enable the use of supercapacitors for energy storage. A theoretical study and comparison of methods, algorithms and techni ... 180. **Disseny i implementació d’un servidor de pàgines web per a la supervisió i difusió de mesures a temps real d’una instal• lació fotovoltaica especı́fica per a la mesura en mòduls fotovoltaics** (2011) — Jorge Querol. In thesis. URL: https://jorge.querol.org/publication/querol-2011-disseny/ - *Abstract*: This research contribution by Jorge Querol (2011), published in international conference proceedings, investigates "Disseny i implementació d’un servidor de pàgines web per a la supervisió i difusió de mesures a temps real d’una instal• lació fotovoltaica especı́fica per a la mesura en mòduls fotovoltaics" within the domains of AI & Neuromorphic SatCom. The work is part of Dr. Jorge Querol's research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.