Robust Design of the Security Scheme in IRS-Assisted MISO Systems with Imperfect Eavesdropping CSI

This paper studies the physical layer security scheme of a multi-input single-output (MISO) wireless communication system. To improve the propagation quality of the channels, intelligent reflecting surface (IRS) is employed. The scenario is considered in the design and optimization of the security scheme that there are multiple eavesdroppers and the channel state information (CSI) of the eavesdropping channels is not accurate. A robust security scheme employing IRS and artificial noise (AN) is designed and optimized. The beamforming of the signal and that of AN and the phase shift matrix of IRS are jointly optimized to promote the secrecy outage transmission rate under the constraint of secrecy outage probability. To solve the non-convex optimization problem, a slack variable is introduced and the problem is transformed into a two-layer optimization problem. The first layer of the optimization is to find the optimal slack variable and the second layer is to find the optimal beamforming and phase shift under a given value of the slack variable. The performance of the proposed scheme is demonstrated by simulation. The simulation results show that the proposed scheme has good robustness and can significantly promote the secrecy outage rate compared with the robust scheme without IRS or the robust scheme without optimal beamforming.