Joint Optimization of Active and Passive Beamforming for RIS-Assisted Secure Communication Under Multiple Eavesdroppers

Abstract

Reconfigurable Intelligent Surface (RIS) facilitates physical-layer secure communications (PSC) by smartly controlling signal features such as phase and amplitude. Previous work shows that an illegal eavesdropper can sharply reduce the capacity for RIS-assisted PSC, while multiple eavesdroppers in the communication system, a more practical and challenging setting in the real world, is still largely underexplored. To this end, we present MuEaRIS, a novel approach that aims to maximize legitimate secure communication rates while minimizing the rate of each illegal eavesdropper for RIS-assisted PSC. Specifically, we jointly optimize Alice’s active beamforming and RIS’s passive beamforming using a novel method that explores alternating optimization and quadratic transformation. Numerical analysis shows that the proposed MuEaRIS is effective for RIS-assisted PSC in multi eavesdropper scenarios, while also outperforming existing methods in single eavesdropper settings, demonstrating broader applicability.