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