Wireless Information and Power Transfer: Optimal Power Control in One-Way and Two-Way Relay System

This paper considers optimal power control solutions in one-way and two-way relay system with simultaneous wireless information and power transfer (SWIPT). First, we develop SWIPT protocols for one-way and two-way relay systems, where two terminals exchange data assisted by an energy-harvesting relay node which gathers energy from the received signal by using a power splitting scheme and forwards the received signal by using the harvesting energy. For one-way relay system, the closed-form solution for optimal power splitting ratio is derived to maximize the system throughput. For asymmetric two-way relay system, we propose a novel power splitting strategy to maximize system throughput. Considering the total transmit power constraints, we develop a semi-closed form solution for power allocation among all nodes by exploiting convex optimization technology. It is shown that the optimal power allocation in two-way relay system would degrade into one-way relay mode if the relay node is close to one of the terminals. For symmetric two-way relay system, a closed-form solution for power allocation and power split ratio is derived. The performances of the three systems are compared numerically. It is revealed that the proposed power allocation algorithm can improve the transmission rate without consuming additional resource compared with non-cooperation relaying scheme.