Enhancing MIMO Covert Communications via Intelligent Reflecting Surface

This letter investigates the multi-input multi-output (MIMO) covert communication aided by intelligent reflecting surface (IRS) against a multi-antenna warden. We establish a design framework for IRS-assisted MIMO covert communication system, which aims to maximize covert rate by jointly optimizing the transmit covariance matrix bf R at transmitter and phase shift matrix bf Q at IRS. Due to the unit modulus constraint of bf Q and the highly coupling of bf R and bf Q , we propose an alternating optimization algorithm to solve it. Specifically, the sub-problem of optimizing bf R for given bf Q is convex, and we can derive a closed-form solution. Then, we propose a minorization-maximization algorithm to tackle the sub-problem of optimizing bf Q for fixed bf R , where we translate the problem to the maximization of a proper lower bound of the objective function which is then solved by the sequential rank-one constraint relaxation algorithm. Simulation results demonstrate the effectiveness and superiority of the proposed algorithm in terms of boosting covert rate under the surveillance of a multi-antenna warden.