Performance of asynchronous two-relay two-hop wireless cooperative networks

In wireless cooperative networks, the asynchronism between the relays can be a source of diversity which is similar in its essence to the multipath diversity of frequency selective channels. In this context, an asynchronous two-relay cooperative wireless network is studied for Decode-and-Forward (DF) and Amplify-and-Forward (AF) protocols. The outage probability in the high Signal to Noise Ratio (SNR) regime is derived and the impact of the relative delay between the two relays on this outage probability is evaluated. It is shown that for a sufficiently high relative delay, the outage probability performance becomes independent from the relative delay and approaches from the synchronous protocol performance. Besides, an optimization of the power distribution between the transmitting nodes of the network is carried out in the high SNR regime based on the outage probability minimization. Moreover, the Diversity Multiplexing Tradeoff (DMT) of the network is characterized for the two cooperative protocols DF and AF. The DMT curve does not depend on the relative delay as long as the latter is non-zero.