RF Energy Harvesting Based Multiple Access Relay Systems: A DMT Perspective

A multiple-access relay system, where the relay node is powered by radio frequency radiation is analyzed in this paper. Specifically, the focus is on the time-switching-based scheme in which the intermediate relay switches between the energy harvesting (EH), information decoding (ID), and the information re-transmission (TX). For this system, we have characterized the diversity-multiplexing trade-off (DMT) for two variants of the EH-based dynamic decode-and-forward (DDF) protocols: without feedback (EH-DDF) and with limited feedback (EH-DDF-LF). Analysis of the protocols reveals that the diversity gain of EHDDF scheme is inferior to that of the traditional non-EH-based DDF protocol. Furthermore, the impact of energy harvesting duration on the DMT performance has been extensively investigated. Consequently, it is observed that the achievable diversity gain of the EH-DDF improves with the reduction in energy harvesting interval. However, there exists a performance difference between the classical non-EH-based DDF and EHDDF even for the minute harvest duration. On the other hand, in the case of EH-DDF-LF, the performance approaches the diversity upper bound in the high multiplexing gain regime. Finally, a detailed comparison of the proposed EH-based schemes has been presented.