Adaptive time-switching and power-Splitting protocols for energy harvesting sensor networks with multiple relays

In the conventional energy-harvesting (EH) relaying protocols based on time switching (TS) and power splitting (PS), the system performance depends on the parameters such as TS and PS ratios. In order to achieve the optimum performance, these parameters need to be optimized. In the distributed cooperative networks, where relay operates independently, the optimization of PS and TS ratios becomes cumbersome and challenging. In this work, we overcome this issue by proposing two relaying protocols referred to as adaptive time-switching (ATS) and adaptive time-switching adaptive power-splitting (ATS-APS) protocols. In the proposed protocols, the relay can dynamically optimize their respective TS and PS ratios according to their local channel condition among relays, i.e., without any external help from the source or destination, which makes the proposed protocols promising for the distributed relaying network. Through rigorous numerical analysis, we show that the proposed protocols can outperform the conventional approach. We also derive mathematical expressions for the outage probability and the effective transmission rate in the framework of decode-and-forward (DF) relaying with partial relay selection (PRS) scheme based on various diversity combining techniques including maximum ratio combining (MRC), selection combining (SC), and selective relaying (SR). Through numerical analysis, we demonstrate that the proposed adaptive SR technique, where the source receives assistance from the relay only if the source-to-destination link is in deep fading, can achieve better performance than the other techniques compared here in terms of the achievable effective transmission rate. All the theoretical results developed are confirmed by numerical simulations.