RIS-enhanced Secure Communication: An Approach of Joint Optimization of Beamforming, RIS Partition and Phase Shifting

In this paper, we investigate the secure communication aided by a reflecting intelligent surface (RIS) and artficial noise (AN). To enhance signal quality for legitimate users while disrupting that of illegitimate ones, we propose deploying a RIS-attached unmanned aerial vehicle (UAV) that hovers above the target network area. Our approach involves virtual partitioning of the RIS, whereby the phase shifts of each partition are optimized to strengthen the desired signal at legitimate users and concurrently amplify the impact of AN on illegitimate users. Aiming to maximize the sum secrecy rate, we jointly optimize beamforming, RIS partition and phase shift. To address the nonconvex problem of maximizing the sum secrecy rate, we decompose the optimization framework into subproblems involving beamforming, RIS partition, and phase shift design, all of which are jointly optimized. The RIS partition is solved using meta-heuristic algorithms, while active and passive beamforming solutions are derived via semi-definite relaxation (SDR) to tackle. Finally, numerical results validate the proposed scheme’s superiority in enhancing the sum secrecy rate.