Secrecy Outage Analysis of RIS-Assisted Multi-User Communications With Phase Errors

Abstract

This paper investigates the physical-layer security (PLS) of a reconfigurable intelligent surface (RIS)-assisted multi-user communication system consisting of a common source, a RIS, and multiple target users in the presence of an eavesdropper. To secure the confidential transmissions from the source to the users via a RIS with finite-resolution phase shifts, we propose the following multi-user scheduling schemes, namely, the secure round-robin scheduling with RIS phase errors (SRS-RPE) and the secure destination selection with RIS phase errors (SDS-RPE) schemes. We derive the closed-form secrecy outage probability (SOP) expressions of the SRS-RPE and SDS-RPE schemes. Numerical results show the correctness of the derived closed-form SOPs of SRS-RPE and SDS-RPE schemes and the agreement of theoretical expressions and simulation results in the low SNR region. Also, the SDS-RPE scheme exhibits its superiority over the SRS-RPE scheme. Additionally, when the number of RIS reflecting elements incrases, the SRS-RPE and SDS-RPE schemes achieve better SOP performance accordingly.