RIS-Assisted UAV Secure Communications With Artificial Noise-Aware Trajectory Design Against Multiple Colluding Curious Users

In this paper, we propose a secure unmanned aerial vehicle (UAV) communication system with the assistance of a reconfigurable intelligent surface (RIS), where the design of the UAV trajectory and artificial noise are incorporated to prevent eavesdropping from multiple colluding curious users. To maximize the secrecy rate of the proposed system, we undertake a joint optimization process that encompasses the trajectory of the UAV, the RIS phase shifts, and the beamforming vectors for both information and artificial noise signals, considering the constraints of the UAV transmit power, UAV flying speed and RIS phase shifts. To address the non-convex nature of the joint problem and handle the coupling effects of multiple parameters, we decompose the problem by using the block coordinate descent (BCD) method, combined with an alternating algorithm to optimize the obtained sub-problems. To further tackle the non-convexity of the sub-problems, we apply the successive convex approximation (SCA) method to tackle the optimization of the trajectory and to optimize the beamformers of information and artificial noise signals, while a majorization-minimization (MM) based scheme is adopted for optimizing the RIS phase shifts. Numerical simulation results substantiate the convergence and effectiveness of the proposed algorithm through the comparison with benchmark methods, and the proposed scheme is proven to achieve a significant improvement in terms of average secrecy rate in various operating conditions.