Manuscript | Dr. Jorge Querol

Terahertz Inter-Satellite Links: Motivation, Challenges and Opportunities

Sat, 05 Sep 2026 00:00:00 +0000

Abstract & Overview

Inter-satellite links (ISLs) are essential to the evolution of next-generation satellite constellations, providing the foundation for low-latency, resilient, and globally scalable connectivity. While low radio-frequency (RF)-based ISLs offer technological maturity, they are increasingly constrained by spectrum scarcity, congestion, and interference. Optical ISLs, on the other hand, deliver unprecedented capacity but demand ultra-precise pointing, suffer from narrow-beam limitations, and are limited to point-to-point links, all of which hinder large-scale deployment, including point-to-multi-point capability. To overcome these limitations, we propose very-high RF terahertz (THz) inter-satellite links (ISLs) as a promising middle-ground solution, merging the ultra-high data rates of optical links with the adaptability, reliability, and relaxed pointing requirements of lower-frequency RF ISLs. However, despite growing interest, research on THz ISLs remains at an early stage, fragmented across isolated studies, and lacking a clear roadmap for practical realization. This paper aims to address this gap by examining the fundamentals of THz ISLs, assessing their potential advantages and key challenges, and identifying the most promising research directions to transform them into a cornerstone of future interconnected mega constellations.

Publication Metadata

Authors: Chandan Kumar Sheemar, Wali Ullah Khan, Giovanni Iacovelli, Sourabh Solanki, Mert Bayraktar, Jorge Querol, Eva Lagunas, Symeon Chatzinotas
Venue: arXiv (Cornell University) (2026)
Research Areas: Satellite Communications
DOI: 10.48550/arxiv.2609.05973

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

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 Communications and Sensing for 6G Satellite Networks: Use Cases and Challenges

Thu, 09 Jan 2025 00:00:00 +0000

Abstract & Overview

Satellite networks (SN) have long provided two fundamental services: global communications and Earth-oriented sensing, supporting applications from connectivity and navigation to disaster management and environmental monitoring. Yet, the accelerating demand for data and the emergence of new applications render the independent evolution of communication and sensing payloads increasingly unsustainable. Joint communications and sensing (JCAS) has emerged as a transformative paradigm, integrating both functions within a unified payload to enhance spectral efficiency, reduce operational costs, and minimize hardware redundancy. Beyond efficiency, this integration creates opportunities for novel services that are infeasible under separate payload designs. This paper motivates the role of JCAS in shaping the sixth-generation (6G) of satellite networks, explores a representative use case to assess its feasibility, and discusses key challenges that must be addressed to unlock its full potential. By highlighting these opportunities inherent to the space environment, we aim to stimulate the development of JCAS as a cornerstone technology for the next-generation space era

Publication Metadata

Authors: Chandan Kumar Sheemar, Prabhu Thiruvasagam, Wali Ullah Khan, Sourabh Solanki, George C. Alexandropoulos, Jorge Querol, Plachy, Jan, Oliver Holschke, Symeon Chatzinotas
Venue: arXiv (Cornell University) (2025)
Research Areas: 6G-NTN, Satellite Communications, JCAS & Earth Observation
DOI: 10.48550/arxiv.2501.05243

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: ArXiv (2024)
Research Areas: Beamforming & MIMO
DOI: 10.1109/icc51166.2024.10622368
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

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: arXiv preprint arXiv:2411.10014 (2024)
Research Areas: 6G-NTN, Beamforming & MIMO
DOI: 10.48550/arXiv.2411.10014

Interference analysis of Positioning Reference Signals in 5G NTN

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

Abstract & Overview

Accurate asset localization holds paramount importance across various industries, ranging from transportation management to search and rescue operations. In scenarios where traditional positioning equations cannot be adequately solved due to limited measurements obtained by the receiver, the utilization of Non-Terrestrial Networks (NTN) based on Low Earth Orbit (LEO) satellites can prove pivotal for precise positioning. The decision to employ NTN in lieu of conventional Global Navigation Satellite Systems (GNSS) is rooted in two key factors. Firstly, GNSS systems are susceptible to jamming and spoofing attacks, thereby compromising their reliability, where LEO satellites link budgets can benefit from a closer distances and the new mega constellations could offer more satellites in view than GNSS. Secondly, 5G service providers seek to reduce dependence on third-party services. Presently, the NTN operation necessitates a GNSS receiver within the User Equipment (UE), placing the service provider at the mercy of GNSS reliability. Consequently, when GNSS signals are unavailable in certain regions, NTN services are also rendered inaccessible.

Publication Metadata

Authors: Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas
Venue: arXiv preprint arXiv:2401.09157 (2024)
Research Areas: 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.48550/arxiv.2401.09157

Optimal Linear Precoding Under Realistic Satellite Communications Scenarios

Mon, 01 Jan 2024 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 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

Performance Evaluation of Neuromorphic Hardware for Onboard Satellite Communication Applications

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

Abstract & Overview

Spiking neural networks (SNNs) implemented on neuromorphic processors (NPs) can enhance the energy efficiency of deployments of artificial intelligence (AI) for specific workloads. As such, NPs represent an interesting opportunity for implementing AI tasks power-limited onboard satellite communication spacecraft. In this article, we disseminate the findings of a recently completed study which targeted the comparison, in terms of performance and power-consumption, of different satellite communication use cases implemented on standard AI accelerators and on NPs. In particular, the article describes three prominent use cases, namely payload resource optimization, onboard interference detection and classification, and dynamic receive beamforming; and compares the performance of conventional convolutional neural networks (CNNs) implemented on Xilinx’s VCK5000 Versal development card, and SNNs on Intel’s neuromorphic chip Loihi 2.

Publication Metadata

Authors: Eva Lagunas, Flor Ortiz, Geoffrey Eappen, Saed Daoud, Wallace Alves Martins, Jorge Querol, Symeon Chatzinotas, Nicolas Skatchkovsky, Bipin Rajendran, Osvaldo Simeone
Venue: arXiv preprint arXiv:2401.06911 (2024)
Research Areas: Satellite Communications, AI & Neuromorphic SatCom, SDR & Experimental Testbeds
DOI: 10.1109/mwc.016.2300560
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

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: arXiv e-prints (2023)
Research Areas: Satellite Communications, Beamforming & MIMO
DOI: 10.48550/arxiv.2311.01366

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

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: Authorea Preprints (2023)
Research Areas: Beamforming & MIMO
DOI: 10.36227/techrxiv.21904665
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: 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

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

System Modelling 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, Nicola Maturo, Symeon Chatzinotas, Björn Ottersten
Venue: arXiv e-prints (2020)
Research Areas: Satellite Communications
DOI: 10.48550/arXiv.2011.09333

System and method for detecting and eliminating radio frequency interferences in real time

Wed, 01 Mar 2017 00:00:00 +0000

Abstract & Overview

This research contribution by Jorge Querol, Adriano Joséé Camps Carmona (2017), published in international conference proceedings, investigates “System and method for detecting and eliminating radio frequency interferences in real time” within the domains of RFI Mitigation & GNSS Security. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: Jorge Querol, Adriano Joséé Camps Carmona
Venue: Conference Paper (2017)
Research Areas: RFI Mitigation & GNSS Security