Optimization of SWIPT With Battery-Assisted Energy Harvesting Full-Duplex Relays

In this article, we investigate the performance of a three-node battery-assisted full-duplex relay (FDR) network which employs simultaneous wireless information and power transfer (SWIPT). The relay augments the harvested energy with battery energy to improve the link performance. Considering both time-switching (TS) and power-splitting (PS) protocols for energy harvesting, we analyze the outage probability and throughput performance with amplify-and-forward (AF) and decode-and-forward (DF) FDRs. For the case of both AF and DF FDRs, we show that a unique value of battery energy exists that maximizes the throughput. Expressions are derived for the throughput-optimal TS and PS parameters. For a desired target throughput, the selection of optimum TS and PS parameters to maximize battery lifetime is discussed. It is demonstrated that for both EH protocols, with low transmit power and a small amount of battery energy, the performance of DF FDRs is superior to that of AF FDRs. In contrast to the case of half-duplex relaying, both TS and PS FDRs achieve a similar throughput at low transmit power, while PS FDR outperforms TS FDR at higher transmit power. Also, when the target throughput is low, TS FDR is more energy-efficient than PS FDR. Monte Carlo simulations confirm the accuracy of the analysis.