Cooperative Communications inWireless Local Area Networks: MAC Protocol Design and Multi-layer Solutions

This dissertation addresses cooperative communications and proposes multi-layer solu- tions for wireless local area networks, focusing on cooperative MAC design. The coop- erative MAC design starts from CSMA/CA based wireless networks. Three key issues of cooperation from the MAC layer are dealt with: i.e., when to cooperate (opportunistic cooperation), whom to cooperate with (relay selection), and how to protect cooperative transmissions (message procedure design). In addition, a cooperative MAC protocol that addresses these three issues is proposed. The relay selection scheme is further optimized in a clustered network to solve the problem of high collision probability in a dense network. The performance of the proposed schemes is evaluated in terms of through- put, packet delivery rate and energy efficiency. Furthermore, the proposed protocol is verified through formal model checking using SPIN. Moreover, a cooperative code allo- cation scheme is proposed targeting at a clustered network where multiple relay nodes can transmit simultaneously. The cooperative communication design is then extended to the routing layer through cross layer routing metrics. Another part of the work aims at enabling concurrent transmissions using cooperative carrier sensing to improve the per- formance in a WLAN network with multiple access points sharing the same channel

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters

Conceção e desempenho de retransmissões sem fios cooperativas

Doutoramento em Engenharia Eletrotécnica/TelecomunicaçõesIn recent years, a new paradigm for communication called cooperative communications has been proposed for which initial information theoretic studies have shown the potential for improvements in capacity over traditional multi-hop wireless networks. Extensive research has been done to mitigate the impact of fading in wireless networks, being mostly focused on Multiple-Input Multiple-Output (MIMO) systems. Recently, cooperative relaying techniques have been investigated to increase the performance of wireless systems by using diversity created by different single antenna devices, aiming to reach the same level of performance of MIMO systems with low cost devices. Cooperative communication is a promising method to achieve high spectrum efficiency and improve transmission capacity for wireless networks. Cooperative communications is the general idea of pooling the resources of distributed nodes to improve the overall performance of a wireless network. In cooperative networks the nodes cooperate to help each other. A cooperative node offering help is acting like a middle man or proxy and can convey messages from source to destination. Cooperative communication involves exploiting the broadcast nature of the wireless medium to form virtual antenna arrays out of independent singleantenna network nodes for transmission. This research aims at contributing to the field of cooperative wireless networks. The focus of this research is on the relay-based Medium Access Control (MAC) protocol. Specifically, I provide a framework for cooperative relaying called RelaySpot which comprises on opportunistic relay selection, cooperative relay scheduling and relay switching. RelaySpot-based solutions are expected to minimize signaling exchange, remove estimation of channel conditions, and improve the utilization of spatial diversity, minimizing outage and increasing reliability.Nos últimos anos foi proposto um novo paradigma de comunicação, chamado de comunicação cooperativa, para o qual estudos iniciais de teoria da informação demonstraram ter potencial para melhorias na capacidade em redes sem fios tradicionais multi-hop. Uma extensa pesquisa tem sido realizada para mitigar o impacto da atenuação em redes sem fios, tendo-se debruçado principalmente em sistemas Multiple-Input Multiple-Output (MIMO). Recentemente têm sido investigadas técnicas de retransmissão cooperativas para aumentar o desempenho de sistemas sem fios, usando a diversidade criada por diferentes antenas individuais com o objetivo de atingir o mesmo nível de desempenho dos sistemas MIMO com dispositivos de baixo custo. A comunicação cooperativa é um método promissor para atingir uma elevada eficiência na ocupação espectral e melhorar a capacidade de transmissão em redes sem fios. A comunicação cooperativa tem por ideia base a junção de recursos de nós distribuídos para melhorar o desempenho global de uma rede sem fios. Em redes cooperativas os nós cooperam para ajudarem-se mutuamente. Um nó cooperativo que ofereça ajuda estará agindo como um intermediário ou mediador, podendo transmitir mensagens da origem para o destino. A comunicação cooperativa explora a natureza da transmissão em difusão das comunicações sem fios para formar antenas múltiplas virtuais com vários nós de rede independentes e com antenas únicas. Esta investigação visou contribuir para a área científica das redes sem fios cooperativas. O foco da pesquisa foi nos protocolos de controlo de acesso ao meio (MAC) com retransmissão cooperativa. Especificamente, proponho uma arquitetura para enquadrar a retransmissão cooperativa, chamada RelaySpot (ponto de retransmissão), que explora a seleção oportunista de retransmissores, o escalonamento de retransmissores cooperativos e a comutação entre retransmissores. As comunicações baseadas na RelaySpot deverão ter uma troca de sinalização reduzida, não usam estimativas das condições do canal e melhoram o aproveitamento da diversidade espacial, minimizando a interrupção e aumentando a fiabilidade

Journal of Telecommunications and Information Technology

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