Secured Wireless Communications Using Multiple Active and Passive Intelligent Reflecting Surfaces

Abstract

This paper presents a novel approach to secure wireless communications by integrating multiple Active and Passive Intelligent Reflecting Surfaces (MAMP-IRSs). We propose a multi-hop beam routing mechanism that leverages active and passive IRSs to establish a secure communication link between a base station and a user to minimize the risk of eavesdropping. Our methodology involves optimizing the beamforming vectors at the base station and the reflection coefficients of the IRSs to maximize the secrecy rate against potential eavesdroppers. This optimization problem exhibits non-convexity, necessitating a computationally Full Search of the solution space. Therefore, we propose two heuristic algorithms: i) Skewed Dijkstra’s Algorithm and ii) Myopic Algorithm. Skewed Dijkstra’s Algorithm utilizes path decomposition and graph theory to identify optimal multi-reflection paths. The Myopic Algorithm looks up only adjacent nodes with a single hop. Numerical simulations demonstrate that Skewed Dijkstra’s Algorithm typically gives a secrecy rate close to the Full Search algorithm, and the Myopic Algorithm gives a narrower performance gap when the number of elements at each passive IRS becomes large.