Topology-assisted techniques to relay selection for homogeneously distributed wireless sensor networks

We consider a multi-relay amplify-and-forward cooperative communication scheme in wireless sensor networks with uniformly distributed nodes. Fixing the average total transmission power from the network and preserving fairness among the selected relays by constraining them to transmit with equal average powers, we aim to improve the signal reception quality at the far-field receiver by means of a proper choice of the relays. Assuming that the nodes' forward channels are not known, the following three relay selection schemes are proposed and their performances are analyzed. 1) Optimal relay selection scheme that maximizes the average SNR at the receiver by exploiting K nodes with the highest SNRs as relays; 2) geometry-based relay selection scheme that is energy-efficient and achieves a close-to-optimal average SNR performance at the receiver by using K closest nodes to the source as relays; and 3) random relay selection scheme that is energy-efficient and further guarantees a fair usage of all nodes by randomly selecting K relays from a specific area around the source. By minimizing an outage probability, a strategy to determine this area is also proposed. Finally, it is shown for all relay selection schemes that the SNR variance at the receiver converges to zero as K increases.