Optimal space-time codes for the MIMO amplify-and-forward cooperative channel

In this work, we extend the non-orthogonal amplify-and-forward (NAF) cooperative diversity scheme to the MIMO channel. A family of space-time block codes for a half-duplex MIMO NAF fading cooperative channel with N relays is constructed. The code construction is based on the non-vanishing determinant criterion (NVD) and is shown to achieve the optimal diversity-multiplexing tradeoff (DMT) of the channel. We provide a general explicit algebraic construction, followed by some examples. In particular, in the single relay case, it is proved that the Golden code and the 4x4 Perfect code are optimal for the single-antenna and two-antenna case, respectively. Simulation results reveal that a significant gain (up to 10dB) can be obtained with the proposed codes, especially in the single-antenna case.Comment: submitted to IEEE Transactions on Information Theory, revised versio

Enhancing diversity and multiplexing gains in multi-user wireless relay systems

The demand for higher transmission rates and better quality of service in modern wireless communications is endless. The use of multiple transmit or /and receive antennas has been considered as one of the most powerful approaches to facilitate high -speed and high -quality communications. However, in practical cellular systems, mobile terminals may not be able to support a multiple- antenna setup. Thus an emerging technique called cooperative diversity is under consideration to utilize the multi -hop relay concept to realize the advantages of multiple - antenna systems in multi -user single- antenna networks. Cooperative diversity has attracted much interest in recent years as a very promising direction for future wireless communication evolution.Due to the fact that in practice terminals cannot transmit and receive simultaneously (i.e. the half -duplex limitation), the diversity improvement brought by the standard cooperative diversity transmission protocols is in general accompanied by a multiplexing loss (equivalent to a reduction in transmission data rate in high signal -to -nose ratio (SNR)). The purpose of this thesis is to use advanced transmission protocols to provide both good diversity and multiplexing performance when using the practical repetition -coded decode - and -forward (DF) relaying strategy in uplink mobile -to -base station transmission of cellular systems.The task is fulfilled by relaxing the orthogonal channel allocation requirement of the standard protocols and by using two relays to take turns forwarding source information to destination. We start our analysis from an M- source two -relay one -destination network. Through diversity -multiplexing tradeoff (DMT) analysis, we prove that for an isolated -relay scenario and a strong -interference scenario, the considered approach effectively recovers the multiplexing loss induced by the standard protocols while still obtaining diversity improvement over direct source -destination transmission without considering relaying.In addition, since the optimal multiplexing gain of the considered system can be achieved by the above approach, we study further improving diversity performance for a two -source network. We analyze taking full advantage of the multiple- source structure, multiple -relay structure, and the capability of affording complex signal processing at the destination (base station). For all three cases, we prove that the diversity performance of the above approach can be enhanced without a significant loss of multiplexing performance or using complex coding strategies at relays. Since the good DMT performance is not affected by source -relay channel conditions, the protocols discussed in this thesis make relaying more beneficial

Propagation measurement based study on relay networks

Von der nächsten Generation von Mobilfunksystemen erwartet man eine umfassende Versorgung mit breitbandigen Multimediadiensten. Um die dafür erforderliche flächendeckende Versorgung mit hohen Datenraten zu gewährleisten, können Relay-Netzwerke einen wesentlichen Beitrag liefern. Hierbei werden Netzwerkstationen mit Relay-Funktionalität in zellulare Netzwerke integriert. Diese Dissertation befasst sich mit der Untersuchung Relay-basierter Netzwerke unter Verwendung von Ausbreitungsmessungen. Die Arbeit deckt Fragen zur Kanalmodellierung, Systemevaluierung bis hin zur Systemverifikation ab. - Zunächst wird ein auf Funkkanalmessungen beruhendes experimentelles Kanalmodell für Relay-Netzwerke vorgestellt. Im Weiteren werden technische Verfahren für Mehrfachzugriffs-Relay-Netzwerke MARN diskutiert. Die erreichbare Systemleistung wurde unter Verwendung von Rayleigh-Kanälen innerhalb einer Systemsimulation bestimmt und im Anschluss mit realen Kanälen, die sowohl direkt aus Funkkanalmessungen als auch indirekt aus dem bereits erwähnten Kanalmodell abgeleitet wurden, verifiziert. Bisherige Arbeiten zur Modellierung breitbandiger Multiple-Input Multiple-Output (MIMO) Kanäle berücksichtigen nicht oder nur sehr stark vereinfacht die Langzeitkorrelationseigenschaften zwischen den Links und werden damit der vermaschten und räumlich weit verteilten Topologie von Relay-Netzwerken gerecht. In der vorliegenden Dissertation erfolgte daher eine experimentelle Untersuchung zu den Korrelationseigenschaften von Large-Scale-Parametern LSP, die unter Verwendung von Funkkanalmessdaten aus urbanen Umgebungen und aus Innenräumen abgeleitet wurden. Die Ergebnisse hierzu fanden Eingang in das vom WINNER-Projekt entwickelte Kanalmodell. Sie erlauben damit eine realistischere Simulation von Relay-unterstützten Netzen. Einen weiteren Schwerpunkt dieser Arbeit stellen technische Verfahren dar, die eine Erhöhung der Systemleistung in MARN mit unbekannter Interferenz UKIF versprechen. Im Einzelnen handelt es sich um die Mehrfachzugriffs-Kodierung MAC - die eine verbesserte Signaltrennung auf der Empfängerseite und eine Erhöhung des Datendurchsatzes erlaubt, den Entwurf eines Relay-Protokolls zur Erhöhung der Systemeffizienz, einen Minimum Mean Square Error (MMSE) Algorithmus zur Unterdrückung unbekannter Interferenzen bei Erhaltung der MAC-Signalstruktur mehrerer Mobilstationen MS, und ein fehlererkennungsbasiertes Signalauswahlverfahren zur Diversitätserhöhung. Die vorgenannten Verfahren werden in einer Systemsimulation zunächst mit Rayleigh-Kanälen evaluiert und demonstrieren die erzielbare theoretische Leistungssteigerung. Die Berücksichtigung realer Funkkanäle innerhalb der Systemsimulation zeigt allerdings, dass die theoretische Systemleistung so in der Realität nicht erreichbar ist. Die Ursache hierfür ist in den idealisierten Annahmen theoretischer Kanäle zu suchen. Für die Entwicklung künftiger Relay-Netzwerke bieten die in dieser Arbeit aufbereiteten Erkenntnisse hinsichtlich der Langzeitkorrelationseigenschaften zwischen den Links einen wertvollen Beitrag für die Abschätzung ihrer Systemleistung auf der Basis eines verbesserten Kanalmodells.Considering technological bases of next generation wireless systems, it is expected that systems can provide a variety of coverage requirements to support ubiquitous communications. To satisfy the requirements, an innovative idea, integrating network elements with a relaying capability into cellular networks, is one of the most promising solutions. The main topic of this dissertation is a propagation measurement based study on relay networks. The study includes three parts: channel modeling, performance evaluation, and verification. First of all, an empirical channel model for relay networks is proposed based on statistical analyses of measurement data. Then, advanced techniques for the throughput improvement and interference cancellation are proposed for Multiple Access Relay Networks (MARN) which are used as an example of relay networks. The performance of the considered MARN is evaluated for Rayleigh channels, and then verified for realistic channels, obtained from measurement data and from the experimental relay channel model as well. For relay channel modeling, the long-term correlation properties between links are of crucial importance due to the meshed-network topology. Although, there is a wide variety of research results for Multiple-Input Multiple-Output (MIMO) channel modeling available, the characterization of correlation properties has been significantly simplified or even completely ignored which motivates this research to be performed. In this dissertation, the experimental results of the correlation properties of Large Scale Parameters (LSP) are presented through the analysis on the real-field measurement data for both the urban and indoor scenarios. furthermore, the correlation properties have been fully introduced into the WINNER channel Model (WIM) for realistic relay channel simulations. As a further contribution of this dissertation, various advanced techniques are proposed for MARN in the presence of Unknown Interference (UKIF). Multiple Access Coding (MAC) is introduced as a multiple access technique. The use of MAC provides the signal separability at the receiver and improves throughput. Thereafter, high system resource efficiency can be achieved through relay protocol design. At the receiver, Minimum Mean Square Error (MMSE)-based spatial filtering is used to suppress UKIF while preserving multiple Mobile Station (MS)s’ MAC-encoded signal structure. Furthermore, an error detection aided signal selection technique is proposed for diversity increasing. The theoretical system performance with aforementioned techniques is simulated for Rayleigh channels. Thereafter, realistic channels are exploited for the performance verification. The gap between the theoretical performance and the realistic performance indicates that the assumptions made to the simplified Rayleigh-channels do not fully hold in reality. For the future relay system design, this work provides valuable information about the performance evaluation of relay networks in consideration of the correlation properties between links

Robust Secure Precoding for UAV-Aided Multi-beam Satellite NOMA Communications

The wide coverage and broadcasting characteristics of satellite communications lead to multi-beam downlinks being vulnerable to security threats, such as eavesdropping, hacking and illegal access. This paper takes into account the case of multiple users and an eavesdropper (Eve) in the target beam. In particular, we consider the deployment of an unmanned aerial vehicle to generate artificial noise in order to confuse Eve, while acting as a relay for the legitimate users. In addition, a nonorthogonal multiple access (NOMA) strategy is used to support multi-user communication and to improve the transmission rate. Considering the constraints due to quality of service, total and per-beam transmit power of the satellite, two robust secure precoding algorithms are presented to maximize the minimal achievable secrecy rate of the legitimate users for both noncritical and critical applications. Since the formulated optimization problems are non-convex, we first use the arithmeticgeometric mean inequality to solve the non-convex constraint of the successive interference cancellation decoding order, and the logarithmic parameter form is addressed by using the first-order Taylor series expansion. Besides, the secure outage probability constraint of the critical case is effectively resolved by applying the Bernstein-type inequality/decomposition-based large deviation inequality. Moreover, semi-definite relaxation and penalty function optimization methods are adopted to design the transmit power of the satellite in two cases, respectively. Simulation results verify the effectiveness and superiority of the proposed robust precoding design methods