Abstract: Based on the intelligent reflecting surface-assisted multi input single output (MISO) secure wireless communication system, we proposed a joint active-passive beamforming algorithm with the objective of maximizing the system secrecy rate. We considered the joint optimization design problem of  beamforming vectors for  base station transmission and passive intelligent reflecting surface (IRS) phase shift matrix under non-ideal channel state information. In order to solve the non-convex fractional planning problem, two auxiliary variables were introduced through Charnes-Cooper transformation to transform the single fractional problem into a difference form, at the same time,  an alternating iterative optimization combined with  semidefinite relaxation (SDR) method was adopted to obtain an easy-to-solve convex problem. The simulation experiment results show that  compared with the traditional algorithms, the proposed algorithm effectively improves the system security, the confidentiality performance by 10%—30%, and the secrecy rate does not decrease significantly under certain channel state information error, which has strong robustness.

Key words: physical layer security, intelligent reflecting surface, statistical channel state information, system secrecy rate, robust beamforming