Flow-Optimized Asynchronous Relay Selection Protocol for Parallel Relay Networks

We investigate the problem of flow optimization in a parallel relay network which consists of a single source sending information to a single destination through multiple relays. The source transmits to the relays using cooperative broadcast and the relays decode and forward the received information to the destination using multiple-access transmission. The relays are operating in half-duplex mode. The flow rates on all links in the network are assigned in a way such that the minimum average transmit power required is minimized. It turns out that not all relays participate in optimal transmission. Using this fact, we propose a sub-optimal relay protocol that employs at most two relays. Simulation results indicate that this sub-optimal protocol gives performance that is close to the performance of the optimal protocol employing multiple relays and superior to that obtained by existing single-relay selection protocols.