Beamforming for Simultaneous Wireless Information and Power Transfer in Two-Way Relay Channels

摘要

This paper studies simultaneous wireless information and power transfer(SWIPT) systems in two-way relaying (TWR) channels. Here, two source nodesreceive information and energy simultaneously via power splitting (PS) from thesignals sent by a multi-antenna relay node. Our objective is to maximize theweighted sum of the harvested energy at two source nodes subject to quality ofservice (QoS) constraints and the relay power constraints. Three well-known andpractical two-way relay strategies are considered, i.e., amplify-and-forward(AF), bit level XOR based decode-and-forward (DF-XOR) and symbol levelsuperposition coding based DF (DF-SUP). For each relaying strategy, weformulate the joint energy transmit beamforming and PS ratios optimization as anonconvex quadratically constrained problem. To find a closed-form solution ofthe formulated problem, we decouple the primal problem into two subproblems. Inthe first problem, we intend to optimize beamforming vector for a given PSratio. In the second subproblem, we optimize the PS ratio with a givenbeamforming vector. It is worth noting that although the correspondingsubproblem are nonconvex, the optimal solution of each subproblem can still befound by using certain techniques. We provide numerical results thatdemonstrate the advantage of adapting the different relaying strategies andweighted factors to harvest energy in two-way relaying channel.