Cooperative Symbol-Based Signaling for Networks with Multiple Relays

Wireless channels suffer from severe inherent impairments and hence reliable and high data rate wireless transmission is particularly challenging to achieve. Fortunately, using multiple antennae improves performance in wireless transmission by providing space diversity, spatial multiplexing, and power gains. However, in wireless ad-hoc networks multiple antennae may not be acceptable due to limitations in size, cost, and hardware complexity. As a result, cooperative relaying strategies have attracted considerable attention because of their abilities to take advantage of multi-antenna by using multiple single-antenna relays. This study is to explore cooperative signaling for different relay networks, such as multi-hop relay networks formed by multiple single-antenna relays and multi-stage relay networks formed by multiple relaying stages with each stage holding several single-antenna relays. The main contribution of this study is the development of a new relaying scheme for networks using symbol-level modulation, such as binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). We also analyze effects of this newly developed scheme when it is used with space-time coding in a multi-stage relay network. Simulation results demonstrate that the new scheme outperforms previously proposed schemes: amplify-and-forward (AF) scheme and decode-and-forward (DF) scheme

Average symbol error rate analysis of reconfigurable intelligent surfaces-assisted free-space optical link over log-normal turbulence channels

Optical wireless communication (OWC) has attracted significant interest recently in academia and industry. Free-space optical (FSO) communication systems are where free space acts as a communication channel between transceivers that are line of sight (LOS) for the successful transmission of optical signals. The FSO transmissions through the atmosphere, nevertheless, bring significant challenges, besides the uncertainty of atmospheric channels, especially the signal fading due to the atmospheric turbulence, attenuation and pointing errors caused by the random beam misalignments between transceivers, signal obstruction due to buildings or trees can pre-vent the transmitted message to reach the destination. This study theoretically investigates the average symbol error rate (ASER) of reconfigurable intelligent surfaces (RIS) assisted FSO link over log-normal turbulence channels. The RIS effect is examined by considering the influence of link distance, transmitted optical power, and quadrature amplitude modulation (QAM) scheme on the ASER

Statistical analysis of the capacity of mobile radio channels

Doktorgradsavhandling i informasjons- og kommunikasjonsteknologi, Universitetet i Agder, Grimstad, 201

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

Hybrid Free-Space Optical and Visible Light Communication Link

V součastnosti bezdrátové optické komunikace (optical wireless communication, OWC) získávají širokou pozornost jako vhodný doplněk ke komunikačním přenosům v rádiovém pásmu. OWC nabízejí několik výhod včetně větší šířky přenosového pásma, neregulovaného frekvenčního pásma či odolnosti vůči elektromagnetickému rušení. Tato práce se zabývá návrhem OWC systémů pro připojení koncových uživatelů. Samotná realizace spojení může být provedena za pomoci různých variant bezdrátových technologií, například pomocí OWC, kombinací různých OWC technologií nebo hybridním rádio-optickým spojem. Za účelem propojení tzv. poslední míle je analyzován optický bezvláknový spoj (free space optics, FSO). Tato práce se dále zabývá analýzou přenosových vlastností celo-optického více skokového spoje s důrazem na vliv atmosférických podmínek. V dnešní době mnoho uživatelů tráví čas ve vnitřních prostorech kanceláří či doma, kde komunikace ve viditelném spektru (visible light communication, VLC) poskytuje lepší přenosové parametry pokrytí než úzce směrové FSO. V rámci této práce byla odvozena a experimentálně ověřena závislost pro bitovou chybovost přesměrovaného (relaying) spoje ve VLC. Pro propojení poskytovatele datavých služeb s koncovým uživatelem může být výhodné zkombinovat více přenosových technologií. Proto je navržen a analyzovám systém pro překonání tzv. problému poslední míle a posledního metru kombinující hybridní FSO a VLC technologie.The field of optical wireless communications (OWC) has recently attracted significant attention as a complementary technology to radio frequency (RF). OWC systems offer several advantages including higher bandwidth, an unregulated spectrum, resistance to electromagnetic interference and a high order of reusability. The thesis focuses on the deployment and analyses of end-user interconnections using the OWC systems. Interconnection can be established by many wireless technologies, for instance, by a single OWC technology, a combination of OWC technologies, or by hybrid OWC/RF links. In order to establish last mile outdoor interconnection, a free-space optical (FSO) has to be investigated. In this thesis, the performance of all-optical multi-hop scenarios is analyzed under atmospheric conditions. However, nowadays, many end users spend much time in indoor environments where visible light communication (VLC) technology can provide better transmission parameters and, significantly, better coverage. An analytical description of bit error rate for relaying VLC schemes is derived and experimentally verified. Nonetheless, for the last mile, interconnection of a provider and end users (joint outdoor and indoor connection) can be advantageous when combining multiple technologies. Therefore, a hybrid FSO/VLC system is proposed and analyzed for the interconnection of the last mile and last meter bottleneck

Wireless Channel Modeling, Simulation, and Estimation

Several emerging wireless communication systems require direct transmission between mobile terminals to support efficient data transfer and user mobility. Such mobile-to-mobile communication systems differ from the conventional cellular systems where only the user unit is mobile. In addition, there might be a relay, also called a repeater, between the original transmitter and the final receiver to improve the network range and coverage. Potential applications for mobile-to-mobile systems include Intelligent Highways for coordinated traffic control and ad-hoc networks meant for military and disaster management. Relays may be deployed in cellular networks and IEEE 802.16 mesh networks for wireless broadband access. Extensive research in cellular radio channels has led to the successful deployment of cellular networks. However, our knowledge of the radio channels encountered in mobile-to-mobile and relay-based systems is still inadequate. This forms the primary motivation behind our research in addressing wireless channel modeling, simulation, and estimation issues for these systems. Specifically, we investigate frequency-flat mobile-to-mobile channels and develop simulation models by using the sum-of-sinusoids method, which is widely used for cellular channels. In addition, we present the properties of amplify and forward relay channels via theoretical analysis. This analysis, to the best of our knowledge, is the first of its kind. Further, we address the unique challenges, which arise because of the different underlying channel model, for channel estimation in amplify and forward relay systems. Our work would provide other researchers the necessary tools for the design and testing of these emerging communication systems.Ph.D.Committee Chair: Stüber, Gordon; Committee Member: Andrew, Alfred; Committee Member: Durgin, Gregory; Committee Member: Ingram, Mary Ann; Committee Member: Li, Geoffre