Optimal Transmit Beamforming for Secure SWIPT in a Two-Tier HetNet

This letter investigates the artificial noise aided beamforming design for secure simultaneous wireless information and power transfer in a two-Tier downlink heterogeneous network (HetNet), where one femtocell underlays one macrocell in co-channel deployment. Each energy receiver in femtocell can be considered as a potential eavesdropper for messages intended for information receiver (IR). Our objective is to maximize the secrecy rate at IR subject to the signal-To-interference-plus noise ratio requirements of macro users, transmit power constraint and energy harvesting constraint. Due to the non-convexity of the formulated problem, it cannot be solved directly. Thus, we propose a novel reformulation by using first-order Taylor expansion and successive convex approximation (SCA) techniques. Furthermore, an SCA-based algorithm with low complexity is proposed to arrive at provably convergent solution. Finally, numerical results evaluate the performance of the proposed algorithm.