Cooperative automatic-repeat-request relaying protocols in wireless networks
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Recently cooperative relaying protocols have been proposed as a way to exploit virtual antenna arrays that provide remarkable capacity improvement in wireless networks. Automatic-repeat-request (ARQ) protocols have been extensively used to enable reliable data packet transmissions at the data link layer. To jointly enhance link connectivity and network reliability in wireless networks, we exploit and propose hybrid-ARQ (H-ARQ) protocols in conjunction with the cooperative communication concept. In this dissertation, we develop and investigate a general framework to study performance improvement and to optimize power assignment for the cooperative H-ARQ relaying protocols based on both an information-theoretic analysis and communication-theoretic analysis. We show that cooperative H-ARQ relaying protocols can dramatically improve performance and reliability of wireless communication networks. First, we develop a new analytical methodology for the evaluation of the outage probability of cooperative decode-and-forward (DF) ARQ relaying protocols. In particular, we derive a closed-form asymptotically tight approximation of the outage probability and develop the optimum power allocation for the DF cooperative ARQ relay scheme. Second, we find the optimal power assignment strategy that minimizes the average total expended transmission power of H-ARQ communications for any targeted H-ARQ link outage probability. We first derive a set of equations that describe the optimal transmission power assignment and enable its exact recursive calculation. We also develop an approximation to the optimal power sequence that is close to the numerically calculated exact result. Third, we consider the problem of assigning optimal transmission power sequence for the cooperative H-ARQ relaying protocol. A closed-form expression of the average total transmission power is obtained first. However, the closed-form expression is complicated, so we develop a simple approximation that is tight at high SNR. Based on the asymptotically tight approximation, we identify the sequence of power values that minimizes the average total power consumption of the cooperative H-ARQ relaying protocol for any given targeted outage probability. Finally, we determine the optimal power assignment strategy that minimizes the average delay of H-ARQ communications over quasi-static Rayleigh fading channels. For any given power budget and any targeted link outage probability, we derive a set of equations that describe the optimal transmission power assignment and prove its optimality based on the Karush-Kuhn-Tucker (KKT) theorem. The newly proposed optimal power assignment scheme outperforms the conventional equal power H-ARQ assignment in terms of minimizing the average delay.