Secure Wireless Communication via Intelligent Reflecting Surface

TLDR

An intelligent reflecting surface (IRS) can adaptively adjust the phase shifts of its reflecting units to strengthen the desired signal and/or suppress the undesired signal. The study investigates an IRS‑aided secure wireless system where a multi‑antenna access point transmits confidential messages to a single‑antenna user while an eavesdropper is present, aiming to maximize secrecy rate through joint AP and IRS beamforming. The authors address a scenario with a stronger, spatially correlated eavesdropper channel by formulating a joint AP and IRS beamforming optimization and solving it with alternating optimization and semidefinite relaxation to obtain a high‑quality suboptimal solution. Simulations demonstrate that the proposed joint beamforming design markedly increases secrecy rate compared to no‑IRS operation and outperforms a heuristic baseline.

Abstract

An intelligent reflecting surface (IRS) can adaptively adjust the phase shifts of its reflecting units to strengthen the desired signal and/or suppress the undesired signal. In this letter, we investigate an IRS-aided secure wireless communication system where a multi-antenna access point (AP) sends confidential messages to a single-antenna user in the presence of a single-antenna eavesdropper. In particular, we consider the challenging scenario where the eavesdropping channel is stronger than the legitimate communication channel and they are also highly correlated in space. We maximize the secrecy rate of the legitimate communication link by jointly designing the AP's transmit beamforming and the IRS's reflect beamforming. While the resultant optimization problem is difficult to solve, we propose an efficient algorithm to obtain high-quality suboptimal solution for it by applying the alternating optimization, and semidefinite relaxation methods. Simulation results show that the proposed design significantly improves the secrecy communication rate for the considered setup over the case without using the IRS, and outperforms a heuristic scheme.