Active IRS Aided Secure Transmission With Hybrid Beamforming

Intelligent reflecting surface (IRS) could boost the security of wireless communications via channel reconfiguration. However, when the direct link is strong, the performance gain introduced by IRS can be insignificant because of the high path loss in the reflecting link. To address this problem, in this correspondence, we deploy the active IRS, which can not only change the incident signal's phase but also amplify its power. Furthermore, artificial noise is also generated to improve the security. We consider a practical scenario where the base station adopts the energy-efficient hybrid analog-digital beamforming (HBF). The sum secrecy rate is maximized via jointly designing the HBF and reflection. Because of the non-convexity, an iterative algorithm is developed to solve the problem. Numerical results show the effectiveness of the proposed scheme.