Wireless-Powered Cooperative Multi-Relay Systems With Relay Selection

In this paper, a wireless-powered cooperative multi-relay network is investigated to enhance the communication quality between two end users. Multiple intermediate relay terminals, which are off-grid and randomly spread within a certain cooperating area, attempt to decode-and-forward the source information to the destination by using the energy scavenged from the source radio-frequency signals. A power splitting architecture is adopted at each relay, where the received signal observation from the source is adaptively divided into two portions for information decoding and energy collection. Then, a single best relay (or relays), according to five different criteria, is selected to forward the decoded source signal to the destination. In view of the spatial randomness and the energy causality at the intermediate relays, stochastic geometry is applied to characterize the end-to-end outage probability of the cooperative multi-relay system considered, based on which the asymptotic outage performance in the high signal-to-noise ratio regime is analyzed. Simulation results demonstrate that with only nominally more knowledge, e.g., locations and charging status of relays, available for relay selection, the communication quality of the system can be substantially improved compared with an arbitrarily random relay selection.