Beamforming & MIMO | Dr. Jorge Querol

Channel Extrapolation based Downlink Precoding using 5G NR Uplink SRS in LEO Satellite

Sun, 24 May 2026 00:00:00 +0000

Abstract & Overview

This research contribution by Ashish Kumar Meshram, Sumit Kumar, Ashok Bandi, Jorge Querol et al. (2026), published in International Conference on Communications, investigates “Channel Extrapolation based Downlink Precoding using 5G NR Uplink SRS in LEO Satellite” within the domains of 6G-NTN, Satellite Communications, Beamforming & MIMO. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: Ashish Kumar Meshram, Sumit Kumar, Ashok Bandi, Jorge Querol, Stefano Andrenacci, Symeon Chatzinotas
Venue: International Conference on Communications (2026)
Research Areas: 6G-NTN, Satellite Communications, Beamforming & MIMO
DOI: 10.1109/icc59461.2026.11587772

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

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

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

Effect of the Cassegrain Telescope on the scintillation of Mathieu-Gauss beams

Thu, 18 Sep 2025 00:00:00 +0000

Abstract & Overview

The scintillation index plays a crucial role in the performance of free space optics (FSO) and quantum key distribution (QKD) systems. Enhancement in the scintillation index causes an increase in the bit error rate and a decrease in the key rate. In this paper, we studied the effect of the Cassegrain telescope on the scintillation of Mathieu-Gauss beams (MGB) in a weak turbulent atmosphere. We model the atmosphere by using the random phase screen numerical approach. We benefit from the hard aperture function when modeling the telescope. We compare the point-like scintillation values with and without the Cassegrain telescope. We research even and odd modes of the MGB. We observe that the scintillation index decreases drastically when using the Cassegrain telescope. In addition, we investigate that the scintillation index decreases when the expansion order rises. Similarly, we see that there is an inverse relation between the first complex expansion coefficient at a short distance. An increase in the second complex expansion coefficient shows its advantage at longer distances by mitigating scintillation. We anticipate that our results will be useful for the optical engineers to design FSO and QKD systems.

Publication Metadata

Authors: Mert Bayraktar, Francesco Vista, Jorge Querol, Yves Schmit, Symeon Chatzinotas
Venue: IEEE International Conference on Space Optical Systems and Applications (ICSOS) (2025)
Research Areas: AI & Neuromorphic SatCom, Beamforming & MIMO, Quantum & Optical Space Links
DOI: 10.1117/12.3063944
Open Access Repository: ORBiLu – University of Luxembourg

Greedy User Scheduling and Beamforming for Holographic Communications

Mon, 07 Jul 2025 00:00:00 +0000

Abstract & Overview

This paper focuses on the challenge of joint hybrid holographic beamforming and user scheduling while guaranteeing per-user minimum Quality-of-Service (QoS) constraints, a key concern in resource-limited wireless networks. However, this problem leads to a mixed-integer non-convex optimization formulation, making it computationally intractable to solve efficiently using conventional methods. To tackle this complexity, we propose an iterative optimization framework that jointly optimizes holographic beamforming patterns and user scheduling to maximize the sum-rate of RHS-assisted networks. Our approach integrates zero-forcing digital beamforming to mitigate interference, a gradient-ascent-based optimization technique for refining holographic beamforming weights, and a greedy User Scheduling strategy to dynamically allocate resources while meeting QoS constraints. Extensive simulation results confirm the effectiveness of our proposed framework, demonstrating significant improvements in sum-rate performance compared to the benchmark algorithm.

Publication Metadata

Authors: Chandan Kumar Sheemar, Christo Kurisummoottil Thomas, Wali Ullah Khan, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas, Walid Saad
Venue: IEEE International Mediterranean Conference on Communications and Networking (MeditCom) (2025)
Research Areas: Beamforming & MIMO
DOI: 10.1109/meditcom64437.2025.11104470

Artificial Intelligence implementation of onboard flexible payload and adaptive beamforming using commercial off-the-shelf devices

Sat, 03 May 2025 00:00:00 +0000

Abstract & Overview

Very High Throughput satellites typically provide multibeam coverage, however, a common problem is that there can be a mismatch between the capacity of each beam and the traffic demand: some beams may fall short, while others exceed the requirements. This challenge can be addressed by integrating machine learning with flexible payload and adaptive beamforming techniques. These methods allow for dynamic allocation of payload resources based on real-time capacity needs. As artificial intelligence advances, its ability to automate tasks, enhance efficiency, and increase precision is proving invaluable, especially in satellite communications, where traditional optimization methods are often computationally intensive. AI-driven solutions offer faster, more effective ways to handle complex satellite communication tasks. Artificial intelligence in space has more constraints than other fields, considering the radiation effects, the spaceship power capabilities, mass, and area. Current onboard processing uses legacy space-certified general-purpose processors, costly application-specific integrated circuits, or field-programmable gate arrays subjected to a highly stringent certification process. The increased performance demands of onboard processors to satisfy the accelerated data rates and autonomy requirements have rendered current space-graded processors obsolete. This work is focused on transforming the satellite payload using artificial intelligence and machine learning methodologies over available commercial off-the-shelf chips for onboard processing. The objectives include validating artificial intelligence-driven scenarios, focusing on flexible payload and adaptive beamforming as machine learning models onboard. Results show that machine learning models significantly improve signal quality, spectral efficiency, and throughput compared to conventional payload.

Publication Metadata

Authors: Luis Manuel Garcés-Socarrás, Amirhosein Nik, Flor Ortíz, Juan Andres Vásquez-Peralvo, Jorge Luis González Ríos, Mouhamad Chehailty, Marcele Kuhfuss, Eva Lagunas, Jan Thoemel, Sumit Kumar, Singh, Vishal, Juan Carlos Merlano Duncán, Sahar Malmir, Swetha Varadajulu, Jorge Querol, Symeon Chatzinotas
Venue: arXiv (Cornell University) (2025)
Research Areas: Beamforming & MIMO
DOI: 10.48550/arxiv.2505.01853

Optimizing Antenna Activation for Even Power Distribution in Multi-Beam Satellite Systems Using Genetic Algorithm

Sun, 30 Mar 2025 00:00:00 +0000

Abstract & Overview

Recent advancements in onboard satellite communication have significantly enhanced the ability to dynamically modify the radiation pattern of a Direct Radiating Array (DRA), which is essential for both conventional communication satellites like Geostationary Orbit (GEO) and those in lower orbits such as Low Earth Orbit (LEO). This is particularly relevant for communication at 28 GHz, a key frequency in the mmWave spectrum, used for high-bandwidth satellite links and 5G communications. Critical design factors include the number of beams, beamwidth, and Side Lobe Level (SLL) for each beam. However, in multibeam scenarios, balancing these design factors can result in uneven power distribution, leading to over-saturation in centrally located antenna elements due to frequent activations. This paper introduces a Genetic Algorithm (GA)-based approach to optimize beamforming coefficients by modulating the amplitude component of the weight matrix, while imposing a constraint on activation instances per element to avoid over-saturation in the Radio Frequency (RF) chain. The proposed method, tested on an 16×16 DRA patch antenna array at 28 GHz for a CubeSat orbiting at 500 km, demonstrates how the algorithm efficiently meets beam pattern requirements and ensures uniform activation distribution. These findings are particularly relevant for emerging satellite systems and 5G networks operating in the mmWave spectrum.

Publication Metadata

Authors: Juan Andres Vásquez-Peralvo, Aral Ertug Zorkun, Jorge Querol, Eva Lagunas, Flor Ortíz, Luis Manuel Garcés-Socarrás, Jorge Luis González Ríos, Symeon Chatzinotas
Venue: European Conference on Antennas and Propagation (2025)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.23919/eucap63536.2025.10999190
Open Access Repository: ORBiLu – University of Luxembourg

Secrecy Rate Maximization for 6G Reconfigurable Holographic Surfaces Assisted Systems

Mon, 03 Mar 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 secrecy rate maximization for an RHS-assisted systems by joint designing the digital beamforming, artificial noise (AN), and the analog holographic beamforming. However, such a problem results to be non-convex and challenging. Therefore, to solve it, a novel alternating optimization algorithm based on the majorization-maximization (MM) framework for RHS-assisted systems is proposed, which rely on surrogate functions to facilitate efficient and reliable optimization. In the proposed approach, digital beamforming design ensures directed signal power toward the legitimate user while minimizing leakage to the unintended receiver. The AN generation method projects noise into the null space of the legitimate user channel, aligning it with the unintended receiver channel to degrade its signal quality. Finally, the holographic beamforming weights are optimized to refine the wavefronts for enhanced secrecy rate performance Simulation results validate the effectiveness of the proposed framework, demonstrating significant improvements in secrecy rate compared to the benchmark method.

Publication Metadata

Authors: Chandan Kumar Sheemar, Wali Ullah Khan, Marco Di Renzo, Asad Mahmood, Jorge Querol, Symeon Chatzinotas
Venue: arXiv (Cornell University) (2025)
Research Areas: 6G-NTN, Beamforming & MIMO
DOI: 10.48550/arxiv.2503.01741

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 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

Demonstration of Safe Electromagnetic Radiation Emitted by 5G Active Antenna Systems

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

Abstract & Overview

The careful planning and safe deployment of 5G technologies will bring enormous benefits to society and the economy. Higher frequency, beamforming, and small-cells are key technologies that will provide unmatched throughput and seamless connectivity to 5G users. Superficial knowledge of these technologies has raised concerns among the general public about the harmful effects of radiation. Several standardization bodies are active to put limits on the emissions which are based on a defined set of radiation measurement methodologies. However, due to the peculiarity of 5G such as dynamicity of the beams, network densification, Time Division Duplexing mode of operation, etc, using existing EMF measurement methods may provide inaccurate results. In this context, we discuss our experimental studies aimed towards the measurement of radiation caused by beam-based transmissions from a 5G base station equipped with an Active Antenna System(AAS). We elaborate on the shortcomings of current measurement methodologies and address several open questions. Next, we demonstrate that using user-specific downlink beamforming, not only better performance is achieved compared to non-beamformed downlink, but also the radiation in the vicinity of the intended user is significantly decreased. Further, we show that under weak reception conditions, an uplink transmission can cause significantly high radiation in the vicinity of the user equipment. We believe that our work will help in clearing several misleading concepts about the 5G EMF radiation effects. We conclude the work by providing guidelines to improve the methodology of EMF measurement by considering the spatiotemporal dynamicity of the 5G transmission.

Publication Metadata

Authors: Sumit Kumar, Chandan Kumar Sheemar, Abdelrahman Astro, Jorge Querol, Symeon Chatzinotas
Venue: arXiv preprint arXiv:2406.07910 (2024)
Research Areas: 6G-NTN, Beamforming & MIMO
DOI: 10.48550/arxiv.2406.07910

Energy-efficient precoding and feeder-link-beam matching design for bent-pipe satcom systems

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

Abstract & Overview

This paper proposes a joint optimization framework for energy-efficient linear precoding and feeder-link-beam matching design in a multi-gateway multi-beam bent-pipe satellite communication system. The proposed scheme jointly optimizes the precoding vectors at the gateway antennas and amplifying-and-matching mechanism at the satellite to maximize the system-weighted energy efficiency under the transmit power budget constraint. The technical designs are formulated into a non-convex sparsity problem consisting of a fractional-form objective function and sparsity-related constraints. To address these challenges, two iterative efficient designs are proposed by utilizing the concepts of Dinkelbach’s method and the compressed-sensing approach. The simulation results demonstrate the effectiveness of the proposed scheme compared to another benchmark method.

Publication Metadata

Authors: Vu Nguyen Ha, Juan Carlos Merlano Duncan, Eva Lagunas, Jorge Querol, Symeon Chatzinotas
Venue: ICC 2024-IEEE International Conference on Communications (2024)
Research Areas: Beamforming & MIMO
DOI: 10.1109/icc51166.2024.10622368
Open Access Repository: ORBiLu – University of Luxembourg

Energy-Efficient Precoding and Feeder-Link-Beam Matching Design for Bent-Pipe SATCOM Systems

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

Abstract & Overview

Publication Metadata

Authors: Vu Nguyen Ha, Juan Carlos Merlano Duncan, Eva Lagunas, Jorge Querol, Symeon Chatzinotas
Venue: ArXiv (2024)
Research Areas: Beamforming & MIMO
DOI: 10.1109/icc51166.2024.10622368
Open Access Repository: ORBiLu – University of Luxembourg

Genetic algorithm-based beamforming in subarray architectures for geo satellites

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

Abstract & Overview

The incorporation of subarrays in Direct Radiating Arrays for satellite missions is fundamental in reducing the number of Radio Frequency chains, which correspondingly diminishes cost, power consumption, space, and mass. Despite the advantages, previous beamforming schemes incur significant losses during beam scanning, particularly when hybrid beamforming is not employed. Consequently, this paper introduces an algorithm capable of compensating for these losses by increasing the power, for this, the algorithm will activate radiating elements required to address a specific Effective Isotropic Radiated Power for a beam pattern over Earth, projected from a GeoStationary satellite. In addition to the aforementioned compensation, other beam parameters have been addressed in the algorithm, such as beamwidth and Side Lobe Levels. To achieve these objectives, we propose employing the array thinning concept through the use of genetic algorithms, which enable beam shaping with the desired characteristics and power. The full array design considers an open-ended waveguide, configured to operate in circular polarization within the Ka-band frequency range of 17.7-20.2 GHz.

Publication Metadata

Authors: Juan Andrés Vásquez-Peralvo, Jorge Querol, Eva Lagunas, Flor Ortiz, Luis Manuel Garcés-Socarrás, Jorge Luis González-Rios, Victor Monzon Baeza, Symeon Chatzinotas
Venue: 2024 18th European Conference on Antennas and Propagation (EuCAP) (2024)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.48550/arxiv.2311.01366

Harnessing Supervised Learning for Adaptive Beamforming in Multibeam Satellite Systems

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

Abstract & Overview

In today’s ever-connected world, the demand for fast and widespread connectivity is insatiable, making multibeam satellite systems an indispensable pillar of modern telecommunications infrastructure. However, the evolving communication landscape necessitates a high degree of adaptability. This adaptability is particularly crucial for beamforming, as it enables the adjustment of peak throughput and beamwidth to meet fluctuating traffic demands by varying the beamwidth, side lobe level (SLL), and effective isotropic radiated power (EIRP). This paper introduces an innovative approach rooted in supervised learning to efficiently derive the requisite beamforming matrix, aligning it with system requirements. Significantly reducing computation time, this method is uniquely tailored for real-time adaptation, enhancing the agility and responsiveness of satellite multibeam systems. Exploiting the power of supervised learning, this research enables multibeam satellites to respond quickly and intelligently to changing communication needs, ultimately ensuring uninterrupted and optimized connectivity in a dynamic world.

Publication Metadata

Authors: Flor Ortiz, Juan A Vasquez-Peralvo, Jorge Querol, Eva Lagunas, Jorge L González Rios, Luis Garces, Victor Monzon-Baeza, Symeon Chatzinotas
Venue: 2024 IEEE International Conference on Machine Learning for Communication (2024)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/icmlcn59089.2024.10624792
Open Access Repository: ORBiLu – University of Luxembourg

High-Resolution 5G Active Antenna Beam Pattern Measurement Using UAVs

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

Abstract & Overview

This paper presents a measurement methodology for obtaining a high-resolution beam pattern of 5G active antenna systems (AASs) using Unmanned Aerial Vehicles (UAVs). Beam pattern measurements are typically conducted in an anechoic chamber by placing the active antenna at the center and radiation pattern is measured at various angles. This approach is limited by the spatial constraints of the chamber and is time-consuming for obtaining high-resolution measurements. To address this problem, UAVs equipped with measurement sensors are proposed to fly around the antenna and do the measurement campaign. The beam pattern measurement campaign problem is formulated into a UAV path planning problem. Horizontal circular arcs at various elevation angles are defined on a sphere centered at the antenna and connected at their ends alternatively to define a reference path and transcribe it into a reference trajectory for the UAV. A chattering-free super-twisting controller is designed to accurately track this trajectory against unknown matched disturbances and model uncertainties. The proposed methodology is validated by an indoor experiment with a horn antenna set up to operate in the frequency range of a 5G AAS and create a stationary beam. A universal software radio peripheral is mounted on a UAV and programmed to measure the received signal strength indicator in real time and a high-resolution beam pattern is satisfactorily captured.

Publication Metadata

Authors: DMKK Venkateswara Rao, Sumit Kumar, Hamed Habibi, Jorge Querol, Symeon Chatzinotas, Holger Voos
Venue: 2024 International Conference on Unmanned Aircraft Systems (ICUAS) (2024)
Research Areas: 6G-NTN, Beamforming & MIMO
DOI: 10.1109/icuas60882.2024.10556877
Open Access Repository: ORBiLu – University of Luxembourg

Holographic MIMO for Next Generation Non-Terrestrial Networks: Motivation, Opportunities, and Challenges

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

Abstract & Overview

Publication Metadata

Authors: Giovanni Iacovelli, Chandan Kumar Sheemar, Wali Ullah Khan, Asad Mahmood, George C. Alexandropoulos, Jorge Querol, Symeon Chatzinotas
Venue: arXiv preprint arXiv:2411.10014 (2024)
Research Areas: 6G-NTN, Beamforming & MIMO
DOI: 10.48550/arXiv.2411.10014

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

Optimal Linear Precoding Under Realistic Satellite Communications Scenarios

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

Abstract & Overview

Publication Metadata

Authors: Geoffrey Eappen, Jorge Luis Gonzalez, Vibhum Singh, Rakesh Palisetty, Alireza Haqiqtnejad, Liz Martinez Marrero, Jevgenij Krivochiza, Jorge Querol, Nicola Maturo, Juan Carlos Merlano Duncan, Eva Lagunas, Stefano Andrenacci, Symeon Chatzinotas
Venue: arXiv preprint arXiv:2408.08621 (2024)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/ojvt.2024.3509646
Open Access Repository: ORBiLu – University of Luxembourg

Supervised Learning Based Real-Time Adaptive Beamforming On-Board Multibeam Satellites

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

Abstract & Overview

Satellite communications (SatCom) are crucial for global connectivity, especially in the era of emerging technologies like 6G and narrowing the digital divide. Traditional SatCom systems struggle with efficient resource management due to static multibeam configurations, hindering quality of service (QoS) amidst dynamic traffic demands. This paper introduces an innovative solution - real-time adaptive beamforming on multibeam satellites with software-defined payloads in geostationary orbit (GEO). Utilizing a Direct Radiating Array (DRA) with circular polarization in the 17.7 - 20.2 GHz band, the paper outlines DRA design and a supervised learning-based algorithm for on-board beamforming. This adaptive approach not only meets precise beam projection needs but also dynamically adjusts beamwidth, minimizes sidelobe levels (SLL), and optimizes effective isotropic radiated power (EIRP).

Publication Metadata

Authors: Flor Ortiz, Juan A Vasquez-Peralvo, Jorge Querol, Eva Lagunas, Jorge L González Rios, Marcele OK Mendonça, Luis Garces, Victor Monzon Baeza, Symeon Chatzinotas
Venue: 2024 18th European Conference on Antennas and Propagation (EuCAP) (2024)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.23919/eucap60739.2024.10501412

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

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

Genetic Algorithm-based Beamforming in Subarray Architectures for GEO Satellites

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

Abstract & Overview

Publication Metadata

Authors: Juan Andrés Vásquez-Peralvo, Jorge Querol, Eva Lagunas, Flor Ortiz, Luis Manuel Garcés-Socarrás, Jorge Luis González-Rios, Victor Monzon Baeza, Symeon Chatzinotas
Venue: arXiv e-prints (2023)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.48550/arxiv.2311.01366

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

Per-link Parallel and Distributed Hybrid Beamforming for Multi-Cell Massive MIMO Millimeter Wave Full Duplex

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

Abstract & Overview

Publication Metadata

Authors: Chandan Kumar Sheemar, Symeon Chatzinotas, Dirk Slock, Eva Lagunas, Jorge Querol
Venue: Authorea Preprints (2023)
Research Areas: Beamforming & MIMO
DOI: 10.36227/techrxiv.21904665
Open Access Repository: ORBiLu – University of Luxembourg

Robust Beamforming for IRS Aided MIMO Full Duplex Systems

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

Abstract & Overview

In this paper, a novel robust beamforming for an intelligent reflecting surface (IRS) assisted FD system is presented. Since perfect channel state information (CSI) is often challenging to acquire in practice, we consider the case of imperfect CSI and adopt a statistically robust beamforming approach to maximize the ergodic weighted sum rate (WSR). We also analyze the achievable WSR of an IRS-assisted FD with imperfect CSI, for which the lower and the upper bounds are derived. The ergodic WSR maximization problem is tackled based on the expected Weighted Minimum Mean Squared Error (WMMSE), which is guaranteed to converge to a local optimum. The effectiveness of the proposed design is investigated with extensive simulation results. It is shown that our robust design achieves significant performance gain compared to the naive beamforming approaches and considerably outperforms the robust Half-Duplex (HD) system.

Publication Metadata

Authors: Chandan Kumar Sheemar, Jorge Querol, Sourabh Solanki, Sumit Kumar, Symeon Chatzinotas
Venue: GLOBECOM 2023-2023 IEEE Global Communications Conference (2023)
Research Areas: AI & Neuromorphic SatCom, Beamforming & MIMO
DOI: 10.48550/arxiv.2308.08016

Signal Processing Based Antenna Pattern Characterization for MIMO Systems

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

Abstract & Overview

Sophisticated antenna technologies are constantly evolving to meet the escalating data demands projected for 6G and future networks. The characterization of these emerging antenna systems poses challenges that necessitate a reevaluation of conventional techniques, which rely solely on simple measurements conducted in advanced anechoic chambers. In this study, our objective is to introduce a novel endeavour for antenna pattern characterization (APC) in next-generation multiple-input-multiple-output (MIMO) systems by utilizing the potential of signal processing tools. In contrast to traditional methods that struggle with multi-path scenarios and require specialized equipment for measurements, we endeavour to estimate the antenna pattern by exploiting information from both line-of-sight (LoS) and non-LoS contributions. This approach enables antenna pattern characterization in complex environments without the need for anechoic chambers, resulting in substantial cost savings. Furthermore, it grants a much wider research community the ability to independently perform APC for emerging complex 6G antenna systems, without relying on anechoic chambers. Simulation results demonstrate the efficacy of the proposed novel approach in accurately estimating the true antenna pattern.

Publication Metadata

Authors: Chandan Kumar Sheemar, Jorge Querol, Symeon Chatzinotas
Venue: 2023 International Conference on Software, Telecommunications and Computer (2023)
Research Areas: Beamforming & MIMO
DOI: 10.23919/softcom58365.2023.10271685
Open Access Repository: ORBiLu – University of Luxembourg

Differential phase compensation in over-the-air precoding test-bed for a multi-beam satellite

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

Abstract & Overview

This article presents a closed-loop differential phase compensation system for a precoding-enabled multibeam satellite forward link and its validation by live experiments on a GEO satellite scenario. The precoding operation avoids inter-beam interference and maximizes the spectrum efficiency by full frequency reuse as an alternative to the traditional two-color or four-color reuse methods proposed in the DVB-S2 standard. However, the satellite payload introduces differential phase and frequency impairments, which can degrade the precoding performance. This work describes the implementation of the differential phase and frequency tracking and compensation loop in an end-to-end testbed over a multibeam satellite system with independent local oscillators. The developed system performs end-to-end real-time communication over the satellite link, including channel measurements and precompensation. Results are validated by an over-the-air demonstration using two beams of the SES-14 multibeam satellite. Each beam is transmitted by independent transponders, which results in differential frequency and phase offsets due to the transponder undisciplined local oscillators. This phase offset makes it impossible to use precoding without the phase compensation loop. We prove that the implemented system can successfully track and compensate the differential phase and frequency to improve precoding performance.

Publication Metadata

Authors: Liz Martínez Marrero, Juan Carlos Merlano Duncán, Jorge Querol, Nicola Maturo, Jevgenij Krivochiza, Symeon Chatzinotas, Björn Ottersten
Venue: 2022 IEEE Wireless Communications and Networking Conference (WCNC) (2022)
Research Areas: Satellite Communications, AI & Neuromorphic SatCom, Beamforming & MIMO
DOI: 10.1109/wcnc51071.2022.9771918
Open Access Repository: ORBiLu – University of Luxembourg

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

Non-coherent massive MIMO integration in satellite communication

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

Abstract & Overview

Massive Multiple Input-Multiple Output (mMIMO) technique has been considered an efficient standard to improve the transmission rate significantly for the following wireless communication systems, such as 5G and beyond. However, implementing this technology has been facing a critical issue of acquiring much channel state information. Primarily, this problem becomes more criticising in the integrated satellite and terrestrial networks (3GPP-Release 15) due to the countable high transmission delay. To deal with this challenging problem, the mMIMO-empowered non-coherent technique can be a promising solution. To our best knowledge, this paper is the first work considering employing the non-coherent mMIMO in satellite communication systems. This work aims to analyse the challenges and opportunities emerging with this integration. Moreover, we identified the issues in this conjunction. The preliminary results presented in this work show that the performance measured in bit error rate (BER) and the number of antennas are not far from that required for terrestrial links. Furthermore, thanks to mMIMO in conjunction with the non-coherent approach, we can work in a low signal-to-noise ratio (SNR) regime, which is an excellent advantage for satellite links.

Publication Metadata

Authors: V.M. Baeza, V.N. Ha, Jorge Querol, S. Chatzinotas
Venue: 39th International Communications Satellite Systems Conference (ICSSC (2022)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.48550/arxiv.2209.09701
Open Access Repository: ORBiLu – University of Luxembourg

Non-Coherent Massive MIMO Integration in Satellite Communication

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

Abstract & Overview

Publication Metadata

Authors: Víctor Monzón Baeza, Vu Nguyen Ha, Jorge Querol, Symeon Chatzinotas
Venue: arXiv preprint arXiv:2209.09701 (2022)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1049/icp.2023.1386

A design strategy for phase synchronization in Precoding-enabled DVB-S2X user terminals

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

Abstract & Overview

This paper address the design of a phase tracking block for the DVB-S2X user terminals in a satellite precoding system. The spectral characteristics of the phase noise introduced by the oscillator, the channel, and the thermal noise at the receiver are taken into account. Using the expected phase noise mask, the optimal parameters for a second-order PLL intended to track channel variations from the pilots are calculated. To validate the results a Simulink model was implemented considering the characteristics of the hardware prototype. The performance of the design was evaluated in terms of the accuracy and stability for the frame structure of superframe Format 2, as described in Annex E of DVB-S2X.

Publication Metadata

Authors: Liz Martinez Marrero, Juan Carlos Merlano Duncan, Jorge Querol, Symeon Chatzinotas, Adriano Camps, Bjorn Ottersten
Venue: ICC 2021-IEEE International Conference on Communications (2021)
Research Areas: Beamforming & MIMO
DOI: 10.1109/icc42927.2021.9500634
Open Access Repository: ORBiLu – University of Luxembourg

Centralized gateway concept for precoded multi-beam GEO satellite networks

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

Abstract & Overview

Satellite Communications offer complementary benefits to terrestrial 5G/6G infrastructure, covering a wide range of use cases in need of ubiquitous coverage and reliability. However, to be as competitive as the terrestrial counterpart in terms of supplied throughput, satellite communications require a highly efficient use of the limited available spectrum. Linear precoding has demonstrated the ability to boost the spectral efficiency in the satellite domain, but raising a new issue: the bandwidth requirements of the feeder link. Deployment of several gateways, each of which precoding an independent cluster of beams causes performance degradation. Therefore, in this paper, we investigate the centralized gateway concept, where all digital baseband processes (including precoding) are implemented in a remote server connected via high speed fibers to the distributed remote gateways responsible for the downlink and uplink of the satellite radio frequency signals. In particular, we highlight the main technical challenges and provide a preliminary vision of potential solutions.

Publication Metadata

Authors: Steven Kisseleff, Eva Lagunas, Jevgenij Krivochiza, Jorge Querol, Nicola Maturo, Liz Martínez Marrero, Juan Carlos Merlano Duncán, Symeon Chatzinotas
Venue: 2021 IEEE 94th Vehicular Technology Conference (VTC2021-Fall) (2021)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.1109/vtc2021-fall52928.2021.9625524
Open Access Repository: ORBiLu – University of Luxembourg

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

Parallel and distributed hybrid beamforming for multicell millimeter wave full duplex

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

Abstract & Overview

Publication Metadata

Authors: Chandan Kumar Sheemar, Symeon Chatzinotas, Dirk Slock, Eva Lagunas, Jorge Querol
Venue: arXiv preprint arXiv: 2112.02335 (2021)
Research Areas: Beamforming & MIMO
DOI: 10.48550/arXiv.2112.02335
Open Access Repository: ORBiLu – University of Luxembourg

Demonstrator of precoding technique for a multi-beams satellite system

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

Abstract & Overview

In this document, we present a real-time demonstrator of precoding technique, to be used to enable full frequency reuse in the forward link of future multi-beam satellite systems. To this aim, our demonstrator will implement all the functionalities required to correctly exploit the achievable gain coming from the usage of precoding. In particular, the main functionality to be included on the User Terminal (UT) side is the proper collection of the estimated Channel State Information (CSI). On the Gateway (GW), a computationally-efficient calculation of the precoding matrix and application of the resulting precoder to the vectors of symbol streams, have to been developed. Using this demonstrator we are able to prove the feasibility of precoding implementation in satellite communications relying on the superframe framing structure defined in Annex E of the DVB-S2X standard.

Publication Metadata

Authors: Nicola Maturo, Juan Carlos Merlano Duncan, Jevgenij Krivochiza, Jorge Querol, Danilo Spano, Symeon Chatzinotas, Björn Ottersten
Venue: 2019 8th International Workshop on Tracking, Telemetry and Command (2019)
Research Areas: Satellite Communications, Beamforming & MIMO, SDR & Experimental Testbeds
DOI: 10.1109/ttc.2019.8895466
Open Access Repository: ORBiLu – University of Luxembourg

Effects of differential oscillator phase noise in precoding performance

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

Abstract & Overview

This research contribution by L. Martinez Marrero, J.C. Merlano Duncan, Jorge Querol, S. Chatzinotas et al. (2019), published in Advances in Communications Satellite Systems. Proceedings of the 37th, investigates “Effects of differential oscillator phase noise in precoding performance” within the domains of Beamforming & MIMO. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: L. Martinez Marrero, J.C. Merlano Duncan, Jorge Querol, S. Chatzinotas, A.J. Camps Carmona, B. Ottersten
Venue: Advances in Communications Satellite Systems. Proceedings of the 37th (2019)
Research Areas: Beamforming & MIMO
DOI: 10.1049/cp.2019.1261

Hardware precoding demonstration in multibeam UHTS communications under realistic payload characteristics

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

Abstract & Overview

In this chapter, we present a new hardware test-bed to demonstrate closed-loop precoded communications for interference mitigation in multibeam ultrahigh throughput satellite systems under realistic payload and channel impairments. We build the test-bed to demonstrate a real-time channel aided precoded transmission under realistic conditions such as the power constraints and satellite-payload nonlinearities. We develop a scalable architecture of an SDR platform with the DVB-S2X piloting. The SDR platform consists of two parts: analog-to-digital (ADC) and digital-to-analog (DAC) converters preceded by radio frequency (RF) front end and field-programmable gate array (FPGA) backend. The former introduces realistic impairments in the transmission chain such as carrier frequency and phase misalignments, quantization noise of multichannel ADC and DAC, and nonlinearities of RF components. It allows evaluating the performance of the precoded transmission in a more realistic environment rather than using only numerical simulations. We benchmark the performance of the communication standard in realistic channel scenarios, evaluate received signal SNR, and measure the actual channel throughput using LDPC codes.

Publication Metadata

Authors: Juan Duncan, Jorge Querol, Nicola Maturo, Jevgenij Krivochiza, Danilo Spano, Norshahida Saba, Liz Marrero, Symeon Chatzinotas, Björn Ottersten
Venue: Advances in Communications Satellite Systems. Proceedings of the 37th (2019)
Research Areas: Beamforming & MIMO, SDR & Experimental Testbeds
DOI: 10.1049/pbte095e_ch66
Open Access Repository: ORBiLu – University of Luxembourg

Beamformer characterization of the MIR instrument: The microwave interferometric reflectometer

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

Abstract & Overview

Global Navigation Satellite Systems - Reflectometry (GNSS-R) has opened promising results for remote sensing applications. The broadcast of new signals with wider bandwidth provides an opportunity to increase the performance of GNSS reflectometry applications. The Microwave Interferometric Reflectometer (MIR) is an instrument being developed to compare different GNSS-R techniques, namely the conventional and interferometric ones, and assess the capabilities of these new signals and bands of the GPS and Galileo systems. This work describes the tests to validate the beamforming system.

Publication Metadata

Authors: R. Onrubia, D. Pascual, Jorge Querol, H. Park, A. Camps
Venue: 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (2017)
Research Areas: Beamforming & MIMO
DOI: 10.1109/igarss.2017.8128132

Advances in the MIR instrument: Integration, control subsystem and analysis of the flight dynamics for beamsteering purposes

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

Abstract & Overview

The MIR (Microwave Interferometric Reflectometer) is a new dual frequency Global Navigation Satellite Systems Reflectometry (GNSS-R) instrument that implements conventional and interferometric reflectometry, both with GPS and Galileo signals. This paper presents the instrument development progress, mainly in the control part, where a methodology to determine how much the platform attitude will affect the beam steering and a satellite selection algorithm have been developed.

Publication Metadata

Authors: R. Onrubia, L. Garrucho, D. Pascual, H. Park, Jorge Querol, A. Alonso-Arroyo, A. Camps
Venue: 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (2015)
Research Areas: Beamforming & MIMO
DOI: 10.1109/igarss.2015.7326895