QoS-Aware Energy Harvesting Relaying Protocol for Multi-Rate SWIPT

This article investigates the performance of a two-hop network in which a source and energy harvesting (EH) relay has multi-rate selection capability and communicates with the destination at different rates. In particular, with fixed and dynamic power-splitting relaying (PSR) protocols, we analyze the system performance of a decode-and-forward (DF) EH relay network using a throughput metric with rate selection. It shows that employing a novel multi-rate scheme improves the throughput drastically over a single rate. Furthermore, we consider joint optimization of the PSR parameter denoted by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rho$</tex-math></inline-formula> and rate selection quality-of-service (RQ) parameter denoted by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula>, which determines the number of transmission rates in the feasible transmission range. In the case of statistical channel state information (CSI) availability, the joint optimization of PSR and RQ parameters is achieved through the 2D golden section search (2D-GSS) method. Closed-form expressions for the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rho$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula> are obtained in case of instantaneous CSI availability. The numerical results demonstrate that the joint parameter optimization with instantaneous CSI provides better performance, and the obtained insights are crucial to improve quality-of-service in energy-constrained wireless networks.