RF Energy Harvesting in Hybrid Two-Way Relaying Systems With Hardware Impairments

In this paper, we investigate the performance of energy harvesting two-way relay systems in the presence of transceiver hardware impairments (HIs). In order to improve the reliability of the communication links, we employ a three-phase hybrid decode-amplify-forward (HDAF) based relaying scheme. In the considered system, the battery-enabled relay node harvests energy from the ambient radio-frequency (RF) signals using a time switching approach. We demonstrate that HIs pose detrimental impact on the performance of system by invoking ceiling effects, primarily when high target rates are anticipated. Consequently, we propose an improved HDAF (IHDAF) relaying scheme which makes the efficient use of available degrees of freedom and thereby enhances the system performance significantly. As such, the IHDAF relaying may induce slightly higher complexity due to involvement of the limited feedback mechanism. However, the benefits offered by this scheme far outweigh its limitation. For the considered system, we derive the user outage probability expressions for both the schemes by applying selection cooperation between direct and relayed links over Nakagami-m fading channels. We also analyze the system throughput and energy efficiency for the two schemes to obtain various useful insights. Finally, numerical and simulation results are provided for the validation of the derived analytical expressions.