Secrecy Analysis for IRS-Aided Wiretap MIMO Communications: Fundamental Limits and System Design

Intelligent reflecting surface (IRS) provides an energy-efficient way to construct channels and enables the joint transceiver and channel design. In this paper, we consider the analysis and design of IRS-aided multiple-input multiple-output (MIMO) secure communications. We first investigate the fundamental limits of IRS-aided wiretap MIMO communications by determining the ergodic secrecy rate (ESR) and secrecy outage probability (SOP), which are not yet available in the literature. For that purpose, we derive the central limit theorem (CLT) for the joint distribution of the mutual information (MI) statistics over IRS-aided MIMO wiretap channels by utilizing random matrix theory (RMT). The CLT is then used to obtain the closed-form expressions for ESR and SOP, which are also extended to the scenario with multiple multi-antenna eavesdroppers. Based on the theoretical results, algorithms for maximizing the artificial noise (AN)-aided ESR and minimizing SOP are proposed. Numerical simulations validate the accuracy of the theoretical results and effectiveness of the proposed optimization algorithms.