Optimal Time-Switching Relaying Protocol for Wireless-Powered DF Relay Networks

This paper proposes a new optimal time-switching relaying protocol for wireless-powered decode-and- forward relay networks. The relay has no embedded power supply, and it has to harvest energy from radio-frequency signals transmitted by the source. In specific, we focus on the time-switching mechanism where a fraction of block time is used for energy harvesting (EH) and the remaining is used for information transmission (IT). Equipped with a rechargeable battery, the relay can accumulate the harvested energy and choose a proper transmit power. For system throughput maximization, we propose an optimal time-switching relaying (TSR) protocol to optimally determine the EH time and the relay power, according to the channel state and the battery state. Interestingly, we prove that the optimal EH time is a discrete two-state variable, i.e., the whole block time is used for either IT or EH. With the proposed TSR relaying protocol, the analytical expression for the system throughput is derived. Simulations validate the analysis and demonstrate that a significant throughput improvement can be achieved.

I. Introduction

Radio-frequency energy harvesting (RF-EH) has emerged as a promising solution to extend the lifetime of energy constrained devices for 5G wireless networks [1]–[3]. The key idea of the RF-EH is that, a device deployed with appropriate circuits can capture the RF radiation and convert it into direct current voltage to support the communication activities [4].