Secrecy Rate Maximization for ARIS-Aided Wireless Powered Communication Networks

This letter considers an active reconfigurable intelligent surface (ARIS)-aided secure wireless powered communication network (WPCN), where an Internet-of-Things (IoT) device first harvests energy from a hybrid access point (HAP), and then transmits the information to the HAP by utilizing the harvested energy in the presence of multiple eavesdroppers (Eves). To maximize the secrecy rate, we propose an ARIS-aided secure communications (ARIS-SC) scheme with the optimization of the energy transmit beamforming and receive beamforming vector of the HAP, the time allocation and the reflection coefficients at the ARIS. To solve the optimization problem, we apply an alternating optimization (AO) method to decouple the original problem into multiple subproblems. Specifically, we derive a closed-form solution for the optimal receive beamforming vector, and the solutions of the energy transmit beamforming vector, the time allocation and the reflection coefficients are obtained by applying successive convex approximation (SCA) technique. Numerical results show that compared with the passive reconfigurable intelligent surface (PRIS) and non-RIS aided communications methods, the proposed ARIS-SC scheme significantly improves secrecy rate.