Artificial Noise Aided Hybrid Analog-Digital Beamforming for Secure Transmission in MIMO Millimeter Wave Relay Systems

Millimeter wave (mm-wave) communications, especially mm-wave relay systems, have been considered as a key technology for next-generation wireless networks due to the rich spectrum resources. However, the problem of information leakage in mm-wave relay systems has not been well investigated. In this paper, artificial noise (AN) aided two-stage secure hybrid beamforming algorithm is proposed in MIMO mm-wave relay system from the perspective of physical layer security. In each time slot of the relay communications, the RF analog beamforming matrices are designed in the first stage, and baseband digital beamforming matrices are designed in the second stage. Through the proposed algorithm, the joint optimization is avoided and the feedback is reduced, which brings low complexity. Moreover, the AN is applied to fight against the eavesdropper by deteriorating the eavesdropping channel. The simulation results show that the proposed hybrid beamforming algorithm considerably improves the performance and achieves a balance between complexity and performance.