Distributed Energy Beamforming and Information Transfer for Multiway Relay Networks

In this paper, we propose a distributed energy beamforming and information transfer (DEBIT) scheme for realizing simultaneous wireless information and power transfer (SWIPT) in multiway relay networks (MWRNs), where multiple users exchange messages with the help of an energy-constrained relay node. We investigate the sum-rate maximization as well as the harvested power maximization problems for the proposed scheme. The resultant sum-rate maximization problem is non-convex and the global optimal solution can be obtained through a 3-D search in combination with convex optimization. To reduce the computation complexity, a suboptimal DEBIT scheme is also proposed, for which the optimization problem becomes linear programming. The achievable sum-rate performance is analyzed and a closed-form lower bound is derived for the MWRN with a large number of users. Furthermore, we consider the harvestedpower maximization problem under a target sum-rate constraint and derive a lower bound of the average harvested power for MWRNs with a large number of users. Numerical results show that the DEBIT scheme significantly outperforms the conventional SWIPT and the derived lower bounds are tight.