Optimum selection relaying protocols in cooperative wireless networks

In this paper, we analyze and compare the outage probabilities of selection relaying protocols for cooperative communications in wireless networks. Depending on the quality of the source-relay channel, the relay may choose either Decode-and-Forward (DF), Amplify-and-Forward (AF), or Direct-Transmission (DT) to forward signals. It turns out that in terms of outage probability, two selection relaying protocols are better than others: either selection between DF and AF protocols (DF-AF) or selection between DF and DT protocols (DF-DT). We show that with an equal power allocation at the source and the relay, both the DF-AF and DF-DT selection protocols have the same asymptotic outage probability. However, with an optimum power allocation strategy, the DF-AF selection is in general better than the DF-DT selection. Simulations are also presented to validate the analytical results.