Article-Journal | Dr. Jorge Querol

Lightweight Deep Learning-Aided LDPC Decoding for 5G NR UAV Communications

Mon, 18 May 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Carla E. García, Jorge Querol, Mario R. Camana, Symeon Chatzinotas
Venue: IEEE Transactions on Aerospace and Electronic Systems (2026)
Research Areas: 6G-NTN, AI & Neuromorphic SatCom
DOI: 10.1109/infocom59046.2026.11571367

Performance analysis of the Cassegrain telescope on the QKD with Mathieu-Gauss Beams

Mon, 11 May 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: S. Oktay, Mert Bayraktar, Francesco Vista, Jorge Querol, Yves Schmit, S. Chatzinotas
Venue: Scientific Reports (2026)
Research Areas: AI & Neuromorphic SatCom, Beamforming & MIMO, Quantum & Optical Space Links
DOI: 10.1038/s41598-026-51915-y
Open Access Repository: ORBiLu – University of Luxembourg

Collaborative Multi-Band Multi-Orbit 6G Satellites with Multi-Connectivity: The Roles of Carrier Aggregation and Dual Connectivity

Fri, 01 May 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Mohammed Al-Ansi, Jorge Querol, Eva Lagunas, Madyan Alsenwi, Symeon Chatzinotas
Venue: IEEE Communications Magazine (2026)
Research Areas: 6G-NTN, Satellite Communications
DOI: 10.1109/mcom.001.2500337
Open Access Repository: ORBiLu – University of Luxembourg

High-Accuracy Ranging in 5G Non-Terrestrial Networks: Receiver Architectures and Interference Analysis

Fri, 01 May 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, José A. del Peral-Rosado, Ivan Lapin
Venue: IEEE Transactions on Vehicular Technology (2026)
Research Areas: 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/navitec202669090.2026.11692531

Automatic RFI Detection, Location, and Classification System in GNSS Bands

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2026)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/jstars.2025.3647776
Open Access Repository: ORBiLu – University of Luxembourg

Holographic Joint Communications and Sensing With Cramér-Rao Bounds

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Chandan Kumar Sheemar, Wali Ullah Khan, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas
Venue: IEEE Journal on Selected Areas in Communications (2026)
Research Areas: JCAS & Earth Observation, Beamforming & MIMO
DOI: 10.1109/jsac.2025.3613282

Holographic Mimo for Next-Generation Nonterrestrial Networks: Motivation, Opportunities, and Challenges

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Giovanni Iacovelli, Chandan Kumar Sheemar, Wali Ullah Khan, Asad Mahmood, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas
Venue: IEEE Vehicular Technology Magazine (2026)
Research Areas: 6G-NTN, Beamforming & MIMO
DOI: 10.1109/mvt.2026.3673016

Impact of Out-of-Band Emissions From Active Antenna Systems on LEO Satellite Downlink Coexistence in the C-Band

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Carla E. García, Michael N. Dazhi, Jorge Querol, Eva Lagunas, Mario R. Camana, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2026)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/ojcoms.2026.3726684

Intelligent Handover Management for Hybrid TN–NTN Mobility in 6G Architectures

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Ons Aouedi, Tedros Salih Abdu, Kha Hung NGUYEN, Eva Lagunas, Jorge Querol, Joël Grotz
Venue: Open Repository and Bibliography (University of Luxembourg) (2026)
Research Areas: 6G-NTN
Open Access Repository: ORBiLu – University of Luxembourg

Joint Beamforming and 3D Location Optimization for Multi-User Holographic UAV Communications

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Chandan Kumar Sheemar, Asad Mahmood, Christo Kurisummoottil Thomas, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas, Walid Saad
Venue: IEEE Transactions on Communications (2026)
Research Areas: Beamforming & MIMO
DOI: 10.1109/tcomm.2026.3663285

Mirage Detector: A Reliable Multiuser Preamble Detector for 6G-NTN

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Ali Georganaki, Jorge Querol, Thang X. Vu, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2026)
Research Areas: 6G-NTN
DOI: 10.1109/ojcoms.2026.3679839
Open Access Repository: ORBiLu – University of Luxembourg

RIS-Enabled Joint Communications and Sensing in 6G NTNs: Opportunities and Challenges

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Wali Ullah Khan, Chandan Kumar Sheemar, Muhammad Ali Jamshed, Eva Lagunas, Jorge Querol, Aryan Kaushik, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2026)
Research Areas: 6G-NTN, JCAS & Earth Observation
DOI: 10.1109/ojcoms.2026.3655070

RPDMA: A PAPR-Aware Multiple Access Scheme

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Goli Srikanth, Shaik Basheeruddin Shah, Nazar T. Ali, Vijay Kumar Chakka, Jorge Querol, Ahmed Altunaiji, Dragan I. Olćan
Venue: IEEE Open Journal of Vehicular Technology (2026)
Research Areas: Satellite Communications, Signal Processing
DOI: 10.1109/ojvt.2026.3661153
Open Access Repository: ORBiLu – University of Luxembourg

Survey on Beyond Diagonal RIS-Enabled 6G Wireless Networks: Fundamentals, Recent Advances, and Challenges

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Wali Ullah Khan, Chandan Kumar Sheemar, Manzoor Ahmed, Marco Di Renzo, Syed Tariq Shah, Asad Mahmood, Eva Lagunas, Jorge Querol, Symeon Chatzinotas, Zhu Han
Venue: IEEE Open Journal of the Communications Society (2026)
Research Areas: 6G-NTN
DOI: 10.1109/ojcoms.2026.3734637
Open Access Repository: ORBiLu – University of Luxembourg

5G-NR Over Transparent Payload GEO Satellites: A Hands-On Approach Using OpenAirInterface5G-NTN

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Sumit Kumar, Jevgenij Krivochiza, Türker Yilmaz, Jorge Querol, Symeon Chatzinotas, Stefano Andrenacci, Joël Grotz
Venue: IEEE Open Journal of the Communications Society (2025)
Research Areas: 6G-NTN, Satellite Communications, AI & Neuromorphic SatCom, SDR & Experimental Testbeds
DOI: 10.1109/ojcoms.2025.3586871
Open Access Repository: ORBiLu – University of Luxembourg

A Vision, Survey, and Roadmap Toward Space Communications in the 6G and Beyond Era

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Konstantinos Ntontin, Eva Lagunas, Jorge Querol, Junaid ur Rehman, Joël Grotz, Symeon Chatzinotas, Björn Ottersten
Venue: Proceedings of the IEEE (2025)
Research Areas: 6G-NTN
DOI: 10.1109/jproc.2024.3512934
Open Access Repository: ORBiLu – University of Luxembourg

Joint Communication and Navigation From LEO Multi-Beam Satellite

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2025)
Research Areas: Satellite Communications, JCAS & Earth Observation, GNSS & Positioning, Beamforming & MIMO
DOI: 10.1109/ojcoms.2025.3568093
Open Access Repository: ORBiLu – University of Luxembourg

Joint Communication and Positioning Receiver Architecture for DSSS-Overlayed OFDM Waveform

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Alejandro Gonzalez-Garrido, Idir Edjekouane, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2025)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.1109/ojcoms.2025.3615957

Joint Holographic Beamforming and User Scheduling With Individual QoS Constraints

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Chandan Kumar Sheemar, Christo Kurisummoottil Thomas, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas, Walid Saad
Venue: IEEE Transactions on Vehicular Technology (2025)
Research Areas: AI & Neuromorphic SatCom, Beamforming & MIMO
DOI: 10.1109/tvt.2025.3569401

Optimal Linear Precoding Under Realistic Satellite Communications Scenarios

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: 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
Venue: IEEE Open Journal of Vehicular Technology (2025)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/ojvt.2024.3509646
Open Access Repository: ORBiLu – University of Luxembourg

Parallel and Distributed Hybrid Beamforming for Multicell Millimeter Wave MIMO Full Duplex

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Chandan Kumar Sheemar, Symeon Chatzinotas, Dirk Slock, Eva Lagunas, Jorge Querol
Venue: IEEE Transactions on Vehicular Technology (2025)
Research Areas: Beamforming & MIMO
DOI: 10.1109/tvt.2024.3488956
Open Access Repository: ORBiLu – University of Luxembourg

Reduced Complexity Initial Synchronization for 5G NR Multibeam LEO-Based Non-Terrestrial Networks

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Ashish Kumar Meshram, Sumit Kumar, Jorge Querol, Stefano Andrenacci, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2025)
Research Areas: 6G-NTN, Satellite Communications, Beamforming & MIMO
DOI: 10.1109/ojcoms.2025.3543625
Open Access Repository: ORBiLu – University of Luxembourg

User Equivalent Range Error and Positioning Accuracy Analysis for ToA-Based Techniques Using PRS and SSB in 5G/6G NTN

Wed, 01 Jan 2025 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2025)
Research Areas: 6G-NTN, GNSS & Positioning
DOI: 10.1109/ojcoms.2025.3623669
Open Access Repository: ORBiLu – University of Luxembourg

Resource-Efficient FPGA Architecture for Real-Time RFI Mitigation in Interferometric Radiometers

Sat, 14 Dec 2024 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Adriano Camps
Venue: Sensors (2024)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, SDR & Experimental Testbeds
DOI: 10.3390/s24248001
Open Access Repository: ORBiLu – University of Luxembourg

Development of a Dynamically Re-Configurable Radio-Frequency Interference Detection System for L-Band Microwave Radiometers

Fri, 21 Jun 2024 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Andreu Mas-Viñolas, A. Amézaga, R. Jove‐Casulleras, Adriano Camps
Venue: Sensors (2024)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.3390/s24134034
Open Access Repository: ORBiLu – University of Luxembourg

5G Non-Terrestrial Networks with OpenAirInterface: An Experimental Study over GEO Satellites

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Florian Völk, Thomas Schlichter, Sumit Kumar, Robert T. Schwarz, Andreas Knopp, Marwan Hammouda, Thomas Heyn, Jorge Querol, Symeon Chatzinotas, Adam Kapovits
Venue: IEEE Access (2024)
Research Areas: 6G-NTN, Satellite Communications, AI & Neuromorphic SatCom, SDR & Experimental Testbeds
DOI: 10.1109/access.2024.3483958
Open Access Repository: ORBiLu – University of Luxembourg

Interference Analysis and Modeling of Positioning Reference Signals in 5G NTN

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2024)
Research Areas: 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/ojcoms.2024.3503692
Open Access Repository: ORBiLu – University of Luxembourg

Multibeam Beamforming for Direct Radiating Arrays in Satellite Communications Using Genetic Algorithm

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: 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
Venue: IEEE Open Journal of the Communications Society (2024)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/ojcoms.2024.3385021
Open Access Repository: ORBiLu – University of Luxembourg

Rate-Splitting Multiple Access for Secure Communications Over CR MISO SWIPT Systems With Non-Linear EH Users

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Carla E. García, Mario R. Camana, Jorge Querol, Symeon Chatzinotas
Venue: IEEE Transactions on Green Communications and Networking (2024)
Research Areas: Satellite Communications, Signal Processing
DOI: 10.1109/tgcn.2024.3404891
Open Access Repository: ORBiLu – University of Luxembourg

Beam centric Doppler pre-compensation for LEO-based 5G-NTN

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Ashish Kumar Meshram, Sumit Kumar, Jorge Querol, Symeon Chatzinotas
Venue: IET Digital Library (2023)
Research Areas: 6G-NTN, Satellite Communications, GNSS & Positioning, Beamforming & MIMO
DOI: 10.1049/icp.2024.0815
Open Access Repository: ORBiLu – University of Luxembourg

End-to-end performance evaluation of slp waveforms

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jevgenij Krivochiza, Juan Carlos Merlano Duncán, Jorge Querol, Symeon Chatzinotas
Venue: IEEE Access (2023)
Research Areas: Satellite Communications, Signal Processing
DOI: 10.1109/access.2023.3327643
Open Access Repository: ORBiLu – University of Luxembourg

Flexible beamforming for direct radiating arrays in satellite communications

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: 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
Venue: IEEE Access (2023)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/access.2023.3300039
Open Access Repository: ORBiLu – University of Luxembourg

IRS Assisted MIMO Full Duplex: Rate Analysis and Beamforming Under Imperfect CSI

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Chandan Kumar Sheemar, Sourabh Solanki, Jorge Querol, Sumit Kumar, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2023)
Research Areas: Beamforming & MIMO
DOI: 10.1109/ojcoms.2023.3306524
Open Access Repository: ORBiLu – University of Luxembourg

Localization as a key enabler of 6G wireless systems: A comprehensive survey and an outlook

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Stylianos E. Trevlakis, Alexandros-Apostolos A. Boulogeorgos, Dimitrios Pliatsios, Jorge Querol, Konstantinos Ntontin, Panagiotis Sarigiannidis, Symeon Chatzinotas, Marco Di Renzo
Venue: IEEE Open Journal of the Communications Society (2023)
Research Areas: 6G-NTN, GNSS & Positioning
DOI: 10.1109/ojcoms.2023.3324952
Open Access Repository: ORBiLu – University of Luxembourg

Onboard processing in satellite communications using ai accelerators

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: 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
Venue: Aerospace (2023)
Research Areas: Satellite Communications, AI & Neuromorphic SatCom
DOI: 10.3390/aerospace10020101
Open Access Repository: ORBiLu – University of Luxembourg

Single-and multi-connectivity for multi-satellite 6G communication networks

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Mohammed Al-Ansi, Jorge Querol, Eva Lagunas, Symeon Chatzinotas
Venue: IET Digital Library (2023)
Research Areas: 6G-NTN, Satellite Communications
DOI: 10.1049/icp.2024.0840

Architectures and synchronization techniques for distributed satellite systems: A survey

Sat, 01 Jan 2022 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Liz Martínez Marrero, Juan Carlos Merlano Duncán, Jorge Querol, Sumit Kumar, Jevgenij Krivochiza, Shree Krishna Sharma, Symeon Chatzinotas, Adriano Camps, Björn Ottersten
Venue: IEEE access (2022)
Research Areas: Satellite Communications
DOI: 10.1109/access.2022.3169499

Machine learning for radio resource management in multibeam GEO satellite systems

Sat, 01 Jan 2022 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Flor Ortíz, Lei Lei, Eva Lagunas, Ramón Martínez Rodríguez‐Osorio, Daniele Tarchi, Jorge Querol, Miguel A. Salas‐Natera, Symeon Chatzinotas
Venue: Electronics (2022)
Research Areas: Satellite Communications, AI & Neuromorphic SatCom, Beamforming & MIMO
DOI: 10.3390/electronics11070992
Open Access Repository: ORBiLu – University of Luxembourg

RFI detection and mitigation for advanced correlators in interferometric radiometers

Sat, 01 Jan 2022 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Adriano Camps, Manuel Martín‐Neira, Martin Süess, Juan Ignacio Ramirez, Alberto Zurita, Joséep Closa, Roger Oliva, R. Onrubia
Venue: Remote Sensing (2022)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.3390/rs14184672

5G-NTN Prototyping and Experimentation Results

Fri, 01 Jan 2021 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Sumit Kumar, Jorge Querol, Symeon Chatzinotas, Marwan Hammouda, Thomas Heyn, Thomas Schlichter, Paulo Marques, Luis Pereira, Roberto Magueta, Florian Völk
Venue: Peer-Reviewed Journal Article (2021)
Research Areas: 6G-NTN

End-to-end precoding validation over a live GEO satellite forward link

Fri, 01 Jan 2021 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jevgenij Krivochiza, Juan Carlos Merlano Duncan, Jorge Querol, Nicola Maturo, Liz Martinez Marrero, Stefano Andrenacci, Jens Krause, Symeon Chatzinotas
Venue: IEEE Access (2021)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.48550/arxiv.2103.11760

Random access procedure over non-terrestrial networks: From theory to practice

Fri, 01 Jan 2021 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Oltjon Kodheli, Abdelrahman Astro, Jorge Querol, Mohammad Gholamian, Sumit Kumar, Nicola Maturo, Symeon Chatzinotas
Venue: IEEE Access (2021)
Research Areas: 6G-NTN
DOI: 10.1109/access.2021.3101291
Open Access Repository: ORBiLu – University of Luxembourg

Wireless and networking technologies for social distancing-indoor and outdoor

Fri, 01 Jan 2021 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jorge Querol, Alejandro González, Vu Nguyen Ha, Sumit Kumar, Symeon Chatzinotas
Venue: Institution of Engineering and Technology eBooks (2021)
Research Areas: Satellite Communications, Signal Processing
DOI: 10.1049/pbte104e_ch3

A remote carrier synchronization technique for coherent distributed remote sensing systems

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Juan Carlos Merlano Duncán, Liz Martínez Marrero, Jorge Querol, Sumit Kumar, Adriano Camps, Symeon Chatzinotas, Björn Ottersten
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2020)
Research Areas: JCAS & Earth Observation
DOI: 10.1109/jstars.2020.3046776
Open Access Repository: ORBiLu – University of Luxembourg

Implementation of a testbed for GNSS-R payload performance evaluation

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Adrián Pérez-Portero, Joan Francesc Muñoz-Martín, Jorge Querol, Hyuk Park, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2020)
Research Areas: JCAS & Earth Observation, GNSS & Positioning, SDR & Experimental Testbeds
DOI: 10.1109/jstars.2020.2997717

L-band vegetation optical depth estimation using transmitted GNSS signals: Application to GNSS-reflectometry and positioning

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Adriano Camps, Alberto Alonso-Arroyo, Hyuk Park, Raul Onrubia, Daniel Pascual, Jorge Querol
Venue: Remote sensing (2020)
Research Areas: JCAS & Earth Observation, GNSS & Positioning, Quantum & Optical Space Links
DOI: 10.3390/rs12152352

Satellite communications in the new space era: A survey and future challenges

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: 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
Venue: IEEE Communications Surveys & Tutorials (2020)
Research Areas: Satellite Communications
DOI: 10.1109/comst.2020.3028247
Open Access Repository: ORBiLu – University of Luxembourg

System modeling and design aspects of next generation high throughput satellites

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Shree Krishna Sharma, Jorge Querol Borras, Nicola Maturo, Symeon Chatzinotas, Bjorn Ottersten
Venue: IEEE Communications Letters (2020)
Research Areas: Satellite Communications
DOI: 10.1109/lcomm.2020.3036593

A review of RFI mitigation techniques in microwave radiometry

Tue, 01 Jan 2019 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jorge Querol, Adrián Pérez-Portero, Adriano Camps
Venue: Remote Sensing (2019)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.3390/rs11243042
Open Access Repository: ORBiLu – University of Luxembourg

The global navigation satellite systems reflectometry (GNSS-R) microwave interferometric reflectometer: Hardware, calibration, and validation experiments

Tue, 01 Jan 2019 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Raul Onrubia, Daniel Pascual, Jorge Querol, Hyuk Park, Adriano Camps
Venue: Sensors (2019)
Research Areas: Satellite Communications, JCAS & Earth Observation, GNSS & Positioning, SDR & Experimental Testbeds
DOI: 10.3390/s19051019

Wind direction signatures in GNSS-R observables from space

Mon, 01 Jan 2018 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Dongliang Guan, Hyuk Park, Adriano Camps, Yong Wang, Raul Onrubia, Jorge Querol, Daniel Pascual
Venue: Remote Sensing (2018)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.3390/rs10020198

A generic level 1 simulator for spaceborne GNSS-R missions and application to GEROS-ISS ocean reflectometry

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Hyuk Park, Adriano Camps, Daniel Pascual, Yujin Kang, R. Onrubia, Jorge Querol, A. Alonso-Arroyo
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2017)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.1109/jstars.2017.2720625

MERITXELL: the Multifrequency Experimental Radiometer with Interference Tracking for Experiments over Land and Littoral—instrument description, calibration and performance

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jorge Querol, J. M. Tarongíi, Giuseppe Forte, Joséé Luís Eguia Gómez, Adriano Camps
Venue: Sensors (2017)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, SDR & Experimental Testbeds
DOI: 10.3390/s17051081

Performance assessment of time--frequency RFI mitigation techniques in microwave radiometry

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jorge Querol, R. Onrubia, A. Alonso-Arroyo, Daniel Pascual, Hyuk Park, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2017)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/jstars.2017.2654541

SNR and standard deviation of cGNSS-R and iGNSS-R scatterometric measurements

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Alberto Alonso-Arroyo, Jorge Querol, Carlos Lopez-Martinez, Valery Zavorotny, Hyuk Park, Daniel Pascual, Raul Onrubia, Adriano Camps
Venue: Sensors (2017)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.3390/s17010183

Crosstalk statistics and impact in interferometric GNSS-R

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Daniel Pascual, Hyuk Park, R. Onrubia, A. Alonso-Arroyo, Jorge Querol, Adriano Camps
Venue: IEEE journal of selected topics in applied earth observations and remote (2016)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.1109/jstars.2016.2551981

DME/TACAN impact analysis on GNSS reflectometry

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: R. Onrubia, Jorge Querol, Daniel Pascual, A. Alonso-Arroyo, Hyuk Park, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2016)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.1109/jstars.2016.2556745

On the correlation between GNSS-R reflectivity and L-band microwave radiometry

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Alberto Alonso-Arroyo, Adriano Camps, Alessandra Monerris, Christoph Rudiger, Jeffrey P. Walker, Raul Onrubia, Jorge Querol, Hyuk Park, Daniel Pascual
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2016)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.1109/jstars.2016.2588281

SNR degradation in GNSS-R measurements under the effects of radio-frequency interference

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Jorge Querol, A. Alonso-Arroyo, R. Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2016)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/jstars.2016.2597438

First results of a GNSS-R experiment from a stratospheric balloon over boreal forests

Thu, 01 Jan 2015 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Hugo Carreno-Luengo, Adriano Camps, Jorge Querol, Giuseppe Forte
Venue: IEEE Transactions on Geoscience and Remote Sensing (2015)
Research Areas: JCAS & Earth Observation, GNSS & Positioning
DOI: 10.1109/tgrs.2015.2504242

Real-time RFI detection and mitigation system for microwave radiometers

Tue, 01 Jan 2013 00:00:00 +0000

Abstract & Overview

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.

Publication Metadata

Authors: Giuseppe F. Forte, Jorge Querol, Adriano Camps, Merce Vall-llossera
Venue: IEEE transactions on geoscience and remote sensing (2013)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/tgrs.2013.2267595