Optimal Secure Relay Beamforming for Non-regenerative Multi-relay Networks with Energy Harvesting Constraint

Considering the existence of eavesdropper, we investigate secure relay beamforming (SRB) problem for simultaneous wireless information and power transfer in non-regenerative multi-antenna multi-relay networks. Our objective is to maximize the achievable secrecy rate subject to sum transmit power constraint at relays and energy harvesting (EH) constraint at EH receiver. By recasting the non-convex optimization problem into a one-variable convex semidefinite programming (SDP), we propose an optimal SDP based one-dimensional search algorithm to solve the problem. To reduce computational complexity, we also proposed a lower complexity suboptimal zero-forcing (ZF)-based SRB scheme which solves only one SDP by replacing the aforementioned variable by its upper bound. It is shown from simulation results that the our proposed suboptimal ZF-based SRB scheme achieves the average achievable secrecy rate which is close to the optimal one.