Considering simultaneous wireless information and power transfer (SWIPT), we investigate joint two sources and the relay beamforming design problem for orthogonal-space–time-block-code (OSTBC)-based amplify-and-forward (AF) multiple-input–multiple-output (MIMO) two-way relay networks in this paper. It is found that to exploit full diversity gain, maximum ratio combining should be employed at the relay, which requires the received signals from two sources at the relay to be aligned and proportional. Thus, unlike conventional relay networks without SWIPT, we propose to employ singular value decomposition (SVD) for both the multiple-access phase and the broadcast phase to parallelize the two-way relay channels, which is optimal in the sense of exploiting full diversity gain. Our objective is to maximize the achievable sum rate under a sum transmit power constraint and an energy harvesting constraint. We propose to solve the formulated optimization problem by alternating optimization combined with the line search method and obtain a locally optimal solution. We also propose a near-optimal solution that simplifies the optimization problem by replacing the objective function with its approximation at a high signal-to-noise ratio (SNR). Simulation results demonstrate that the proposed two-way relay network has significant performance improvement over the one-way relay network.
['Qi Zhang', 'Quanzhong Li', 'Jiayin Qin']
Beamforming Design for OSTBC-Based AF-MIMO Two-Way Relay Networks With Simultaneous Wireless Information and Power Transfer