Enhancing Security Performance in Wireless Communication Systems via Multiple Reconfigurable Intelligent Surfaces Assistance

Abstract This paper proposes a method for enhancing the security of wireless communication systems aided by multiple reconfigurable intelligent surfaces (RISs). The method considers not only the interactions between multiple RISs and the resulting multi-channel cascades, but also the potential eavesdropping threats to legitimate user communications. To solve the problem of maximizing secrecy rate, this paper proposes an efficient alternating optimization (AO) algorithm. The algorithm achieves joint optimization of base station beamforming and RIS phase shifts by iteratively applying sequential convex approximation (SCA) and semidefinite relaxation (SDR) techniques. The algorithm can effectively transform the complex non-convex optimization problem into a series of subproblems, and then iteratively optimize these subproblems alternately to ultimately obtain a high-quality solution to the original problem. The simulation results show that the multi-RIS aided communication system greatly improves the security performance compared to the single RIS and dual RIS system. Additionally, a comparative evaluation with three other algorithms from the literatures reveals that the proposed method outperforms existing solutions under identical parameter settings, highlighting the superiority of multi-RIS co-optimization in mitigating eavesdropping threats and enhancing information confidentiality. At the same time, we also compare the impacts of real-world situations, such as imperfect channel state information and RIS discrete phase shifts, on the security performance of multi-RIS systems. This reserach provides valuable theoretical guidance and research directions for the future implementation of multi-RIS systems in real-world scenarios.