Joint Trajectory and Passive Beamforming Design for Secure UAV Networks with RIS

Abstract

This paper investigates the problem of secure energy efficiency maximization for a reconfigurable intelligent surface (RIS) assisted uplink wireless communication system, where an unmanned aerial vehicle (UAV) equipped with an RIS works as a mobile relay between the base station (BS) and a group of users. We focus on maximizing the secure energy efficiency of the system via jointly optimizing the UAV’s trajectory, the RIS’s phase shift, user association and transmit power. To tackle this problem, we divide the original problem into three sub-problems, and propose an efficient iterative algorithm. In particular, the successive convex approximation (SCA) method is applied to solve the nonconvex UAV trajectory, the RIS’s phase shift, and transmit power optimization sub-problems. Simulation results demonstrate that the proposed algorithm converges fast, and the proposed design can enhance the secure energy efficiency by up to 38% gains, compared to the traditional schemes without any RIS.