Cooperative communication to minimize the outage probability in a hard real-time scenario
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Cooperative communication is one of the most recent techniques to improve the performance in wireless networks, in terms of increasing the throughput or improving the reliability. It consists in using some of the nodes of the network as relays that forward the source message to the destination achieving a spatial diversity gain, often referred to as cooperative diversity gain. There are a lot of research investigations dealing with this topic from several points of view, but the application of this strategy to hard realtime scenarios that have very high quality-of-service requirements is not studied yet. This research topic has emerged as an active and fertile field of a growing number of researchers and many major advances are expected in the next few years. In this thesis we focus on this research field. In most of the cooperative communication protocols, developed by the researchers, only one relay station is used and in some cases without a best relay selection algorithm. We consider the use of multiple relays and we select the best relaying scheme that optimizes the performance in terms of minimizing the outage probability. We first study in a theoretical way which is the optimum number of relays and how the location of the relays affects the outage probability. After that, we design two different algorithms that select the best relaying scheme. Then we present a modification of a token passing medium access control protocol in order to implement this strategy. Finally, as a proof of concept, we implement this protocol modification in a real environment with the use of FPGA boards and we evaluate the resulting performance. Results show that we achieve a reduction of 75% in packet losses in the best case scenario.