Securing Double-RIS Aided Multi-User Communication Against Multiple Eavesdroppers

This paper considers a scenario involving a network where two reconfigurable intelligent surfaces (RISs) contribute to enhancing the security of multi-user secure downlink communication, even in the presence of multiple potential eavesdroppers. The objective is to optimize the base station (BS)'s beamforming and the quantized programmable reflecting elements (PREs) of both RISs to maximize the geometric mean of secrecy rates (GM-SECR). To tackle this intricate non-convex penalized optimization problem, the paper introduces an alternating descent iteration algorithm based on closed-form solutions. Through simulations, the study highlights the advantages presented by the proposed double-RIS system and validates the efficacy of the algorithm. Notably, the results demonstrate a marked enhancement in achieving fair distributions of secrecy rates.