Secure Hybrid Beamforming with Low-Resolution Phase Shifters in mmWave MIMO Systems

Millimeter wave (mmWave) communications with large-scale antenna arrays and hardware-efficient analog/digital hybrid beamforming have been widely considered as one of the key technologies to enable very high data rate in the fifth generation (5G) applications. Meanwhile, physical layer security (PLS) in mmWave wiretap systems and secure hybrid beamformer designs have drawn increasing attention to safeguard 5G-and-beyond networks. However, in existing literatures, infinite or high-resolution phase shifters (PSs) are often assumed to implement fine-tunable analog beamformers, which are impractical due to high hardware cost and power consumption. In this paper, we consider the problem of hybrid beamformers design with practical
low-resolution
PSs for secure transmission in mmWave wiretap multi-input multi-output (MIMO) systems. We aim to develop secure hybrid beamforming algorithms to maximize the secrecy rate according to different availabilities of eavesdropper's channel state information (CSI). Particularly, when eavesdropper's CSI is available, the proposed algorithm first determines the secure analog beamformers by an iterative algorithm, then finds the digital beamformers which can further enhance the security. If eavesdropper's CSI is unknown, we develop an artificial noise (AN)-based secure hybrid beamforming approach. Simulation results demonstrate that our proposed algorithms can provide significant secrecy performance improvement.