Hybrid Precoding for IRS-assisted Secure mmWave Communication System with SWIPT

This paper investigates the intelligent reflecting surface (IRS)-assisted secure transmission with simultaneous wireless information and power transfer (SWIPT) for mmWave multiple-input multiple-output (MIMO) system. To address the great pathloss and terrible performance caused by the blockage, we propose a hybrid scheme which is a joint optimization of hybrid precoders of transceiver and phase of IRS, to maximize the secrecy rate and reduce the risk of information leakage from the energy havesting receiver (EHR). Firstly, to reduce the complexity, we use a codebook-design method to design analog beamformer. Then, we divide this problem into two semi-definite programming (SDP) functions of digital precoders and phase shifts of IRS with non-convex rank-one constraints. Next, we employ a successive convex approximation (SCA)-based iterative algorithm which is difference of concave (D.C.) functions with penalty items to solve the formulated problem. Finally, we can recover the original variables in a nearly perfect way comparing with the well-known Gaussian randomization approximation (GRA) method which is commonly used. Simulation results show that IRS can enhance the secure performance of mmWave communication system, and the proposed hybrid design can achieve the performance of conventional linear precoder scheme but with much less power consumption.