Impact of Scheduling in the Return-Link of Multi-Beam Satellite MIMO Systems

The utilization of universal frequency reuse in multi-beam satellite systems introduces a non-negligible level of co-channel interference (CCI), which in turn penalizes the quality of service experienced by users. Taking this as starting point, the paper focuses on resource management performed by the gateway (hub) on the return-link, with particular emphasis on a scheduling algorithm based on bipartite graph approach. The study gives important insights into the achievable per-user rate and the role played by the number of users and spot beams considered for scheduling. More interestingly, it is shown that a free-slot assignment strategy helps to exploit the available satellite resources, thus guaranteeing a max-min rate requirement to users. Remarks about the trade-off between efficiency-loss and performance increase are finally drawn at the end of the paper.Comment: Submitted and accepted to IEEE GLOBECOM 2012 Conference, 6 pages, 10 figure

Next Generation High Throughput Satellite System

This paper aims at presenting an overview of the state-of-the-art in High Throughput Satellite (HTS) systems for Fixed Satellite Services (FSS) and High Density-FSS. Promising techniques and innovative strategies that can enhance system performance are reviewed and analyzed aiming to show what to expect for next generation ultra-high capacity satellite systems. Potential air interface evolutions, efficient frequency plans,feeder link dimensioning strategies and interference cancellation techniques are presented to show how Terabit/s satellite myth may turn into reality real soon

On the Throughput of Large-but-Finite MIMO Networks using Schedulers

This paper studies the sum throughput of the {multi-user} multiple-input-single-output (MISO) networks in the cases with large but finite number of transmit antennas and users. Considering continuous and bursty communication scenarios with different users' data request probabilities, we derive quasi-closed-form expressions for the maximum achievable throughput of the networks using optimal schedulers. The results are obtained in various cases with different levels of interference cancellation. Also, we develop an efficient scheduling scheme using genetic algorithms (GAs), and evaluate the effect of different parameters, such as channel/precoding models, number of antennas/users, scheduling costs and power amplifiers' efficiency, on the system performance. Finally, we use the recent results on the achievable rates of finite block-length codes to analyze the system performance in the cases with short packets. As demonstrated, the proposed GA-based scheduler reaches (almost) the same throughput as in the exhaustive search-based optimal scheduler, with substantially less implementation complexity. Moreover, the power amplifiers' inefficiency and the scheduling delay affect the performance of the scheduling-based systems significantly

Symbol-asynchronous transmission in multibeam satellite user down-link : rate regions for novel superposition coding schemes

We consider the forward link of a multibeam satellite system with high spectral reuse and the novel low-complexity transmission and detection strategies from [1]. More specifically, we study the impact of a time offset between the antenna beams that cooperate to simultaneously serve a given user. Assuming Gaussian signaling, we provide closed-form expressions for the achievable rate region. It is demonstrated that, in the absence of timing information at the gateway, this region is not affected by a time offset. Our numerical results further show that, in case timing is known at the gateway, an offset of half a symbol period at both user terminals is optimal in terms of spectral efficiency.Grant numbers : Satellite Network of Experts IV. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Message-splitting for interference cancellation in multibeam satellite systems

This paper investigates a novel technique to deal with the interference in the forward link of multibeam satellite systems when aggressive frequency reuse schemes are employed. Taking into account only magnitude information about the forward channel, the gateway judiciously splits the messages to be transmitted into private and public parts. At the receive terminals, partial cancellation of the public messages is applied prior to private message detection. The practical significance of the absence of channel phase information is stressed and complemented by some additional insights on the implementation. Our numerical results show that, in terms of average total throughput, this technique combined with a 2-colour frequency reuse scheme can outperform a classic orthogonal system with a conservative 4-colour frequency reuse scheme, despite the additional co-channel interference.Grant numbers : SatNEx IV - Satellite Network of Experts IV. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Study on the application of NOMA techniques for heterogeneous satellite terminals

This paper addresses the application of nonorthogonal multiple-access techniques (NOMA) to those satellite relayed communications for which a significant imbalance in the link quality of user terminals can be expected. The Signal-to-Interference and Noise Ratio (SINR) imbalance could be caused by the coexistence of different types of terminals, possibly with different antenna sizes, and offering different classes of service. This link SINR asymmetry can be exploited to outperform orthogonal access schemes under different rate metrics, paying special attention to fairness in the service provision. Both forward and asynchronous return link are addressed, with minimum signaling information and emphasis on some relevant implementation issues such as framing and synchronization

Interference Management and Energy Efficiency in Satellite Communications

The main areas of research of this thesis are Interference Management and Link-Level Power Efficiency for Satellite Communications. The thesis is divided in two parts. Part I tackles the problem of interference environments in satellite communications, and interference mitigation strategies, not just in terms of avoidance of the interferers, but also in terms of actually exploiting the interference present in the system as a useful signal. The analysis follows a top-down approach across different levels of investigation, starting from system level consideration on interference management, down to link-level aspects and to intra-receiver design. Interference Management techniques are proposed at all the levels of investigation, with interesting results. Part II is related to efficiency in the power domain, for instance in terms of required Input Back-off at the power amplifiers, which can be an issue for waveform based on linear modulations, due to their varying envelope. To cope with such aspects, an analysis is carried out to compare linear modulation with waveforms based on constant envelope modulations. It is shown that in some scenarios, constant envelope waveforms, even if at lower spectral efficiency, outperform linear modulation waveform in terms of energy efficiency

Energy and rate allocation for massive multiple access with interference cancelation

This article addresses the problem of energy and code allocation to many users accessing, under spreading-based nonorthogonal multiple access, a wireless node set up with a successive interference cancellation architecture aided by redundancy-check error control. As an application, we consider the asynchronous access of a delay-tolerant satellite system, where users employ finite-length channel codes and are subject to a known power unbalance induced by the known distribution of the channel’s attenuation. The article develops, as a mathematically tractable approximation to massively populated systems, a unified framework to compute the best energy and code allocation rules that maximize the spectral efficiency of a network that handles asymptotically many users. Concretely, the presented approach circumvents the exponential complexity in the number of users when modeling the propagation of packet decoding failures through the receiver’s decoding scheme. It also enables a deterministic analysis of the more complex features affecting the receiver, making the related performance optimization problem amenable to systematic tools from differential and variational calculus. The derived expressions evidence the most favorable three-way unbalance between energy, rate, and reliability for receiver performance. Low-level system simulations are carried out for validation.This work was supported in part by the Spanish Ministry of Science and Innovation through project RODIN (PID2019-105717RB-C22/AEI/10.13039/501100011033) and in part by Grant 2017 SGR 578.Peer ReviewedPostprint (published version

Performance of Adaptive Satellite Antenna Array Processing and Comparison with Optimal Multi-User Communications

Eine Methode eine hohe spektrale Effizienz in Satellitenkommunikationssystemen zu erzielen, ist die koordinierte Wiederverwendung von Frequenzen in ausreichend voneinander entfernten geographischen Regionen. Die Frequenzwiederverwendung und damit die spektrale Effizienz können durch den Einsatz von Maßnahmen maximiert werden, die die Interferenz von nahe benachbarten Gleichkanal-Nutzern effizienter unterdrücken. In der Literatur kann man zwei fundamental unterschiedliche Ansätze finden, die eine bessere Unterdrückung der Interferenz von Gleichkanal-Nutzern ermöglichen. Der erste Ansatz fußt auf Dekodierungsmethoden, die durch die informationstheoretische Beschreibung des Mehrfachzugriffskanals (multiple access channel (MAC)) nahegelegt werden. Als eine der Möglichkeiten stellt Sukzessive Dekodierung (successive decoding) dabei eine attraktive Alternative zu komplexeren Verfahren dar, weil die Komplexität einerseits nur linear mit der Zahl der Quellen ansteigt und weil mit gewissen Einschränkungen dieselben Informationsraten erreicht werden können wie mit der optimalen Verbunddekodierung. Der zweite Ansatz versucht die räumliche Verteilung der interferierenden Gleichkanal-Nutzer effizient zu nutzen, indem eine Gruppenantenne (antenna array) zusammen mit adaptiver Strahlformung (adaptive beamforming) am Satelliten eingesetzt wird. Folgende Fragestellungen ergeben sich innerhalb des oben beschriebenen Rahmens: Ist es möglich, die oben beschriebenen Empfängervarianten, die entweder feste oder adaptive Strahlformung, bzw. entweder unabhängige oder sukzessive Dekodierung anwenden, in einer einheitlichen Weise zu beschreiben? Gibt es eine einfache Lösung für das Problem der Ressourcenzuteilung, die Sendeleistungen den Quellen zuzuordnen, welche notwendig sind, um eine bestimmte Informationsrate für alle Quellen zu erzielen? Wie ist die Leistungsfähigkeit eines Empfängers, der adaptive Strahlformung und/oder sukzessive Dekodierung anwendet, im Vergleich zu einem Empfänger, der feste Strahlformung und unabhängige Dekodierung einsetzt, wie es heutzutage der Standard ist? Wie nahe liegt die Leistung des Empfängers, der sowohl adaptive Strahlformung, als auch sukzessive Dekodierung verwendet, an der des Empfängers, der nur entweder adaptive Strahlformung oder sukzessive Dekodierung verwendet? Ist der Empfänger, der feste Strahlformung mit sukzessiver Dekodierung implementiert, besser als der, der adaptive Strahlformung mit unabhängiger Dekodierung implementiert, oder umgekehrt? Wie hängen die Antworten auf obige Fragen ab von der jeweiligen Quellenverteilung und dem daraus resultierenden Interferenzszenario