Relay selection schemes to minimise outage in wireless powered communication networks

In this study, the authors discuss relay selection schemes with the objective to minimise outage probability for a network consisting of a single source, multiple relays and a single destination. The relays are powered by radio frequency signals from the source. For a successful transmission, at least one of the relay nodes should be able to decode the source signals and have enough energy to relay the information to the destination. The authors assume that a relay node cannot decode information and harvest energy from the source signals simultaneously. The authors formulate an optimisation problem to minimise outage probability for the system. The relay selection scheme and the outage performance depend on the availability of the channel state information (CSI) on the source-relay and the relay-destination links. Based on the availability of the CSI on the relay-destination link, the authors propose relay selection schemes for different scenarios and evaluate the performance numerically. The results show that the availability of the CSI on the relay-destination link at the relay node helps to improve the outage performance considerably. The authors characterise the outage probability for the schemes analytically; and numerically compute the optimal number of relays which provide the optimal outage performance for a given scheme.