Jointly optimizing power allocation and relay positions for multi-relay regenerative relaying with relay selection

In this paper, we consider a dual-hop regenerative relay system consisting of one source node, one destination node and multiple relay nodes. All nodes are equipped with a single antenna except the destination node. We discuss two different relay selection strategies: 1) selection of the best relay; and 2) selection of all reliable relays. We investigate the optimal power allocation (PA) and relay positioning problem under each relay selection strategy. With the second order channel statistics, we jointly optimize PA and relay locations to reduce the system outage probability. Simulation results show that our proposed adaptive allocation algorithms significantly outperform the existing allocation algorithms. It turns out that the strategy of selecting the best relay has better performance than the strategy of selecting all reliable relays. For both relay selection strategies, all relays have to be scattered in a small region on the line through the source and destination. With joint optimization, it is interesting to find that the optimal source power ratio is equal to the optimal relative source-relay distance.