Joint Resource Allocation Optimization in OFDM Relay Networks with SWIET

Simultaneous Wireless Information and Energy Transfer (SWIET) is a promising energy harvesting technique to power energy-constrained wireless nodes in wireless communications. In wireless relay networks, employing SWIET at the source-to-relay link, an energy-constrained relay node can harvest energy from the radio-frequency (RF) signals transmitted by a source node while assisting information relaying, and thus its lifetime can be prolonged. In this paper, we investigate an orthogonal-frequency-division multiplexing (OFDM) amplify-and-forward (AF) relay network with SWIET. The goal is to maximize the end-to-end achievable rate. Unlike the work in literature where only peak transmit power constraint at source is considered, we consider both peak and average transmit power constraints at source, by which the operation time of the source's batteries can be extended. The formulated problem is non-convex because the average transmit power constraint at source and the EH constraint at relay are non-convex. To tackle this non-convex problem, we transform it into two fractional programming problems. By solving the two fractional programming problems with Dinkelbach's procedure, we propose two algorithms to achieve optimal resource allocations. Simulation results verify the optimality of our proposed resource allocation scheme and show that the average power constraint at source has much impact on the end-to-end achievable rate of the SWIET-based OFDM AF relay network.