Secure transmission using lens antenna array in millimeter wave MISO systems

Abstract

In this paper, we investigated an approach to achieve secure transmission using lens antenna array (LAA) in millimeter wave (mmWave) MISO systems. Unlike the conventional sub-6GHz communication system, mmWave communication systems are difficult to implement with full digital beamforming. Thus, the mmWave communication system is implemented with hybrid beamforming architecture, which is composed with analog beamforming and digital beamforming. In this paper, the analog beamformer is replaced with lens antenna array (LAA) to decrease its complexity for secrecy capacity maximization problem. It is obtained that guaranteeing the physical layer security with antenna selection scheme and artificial noise through the LAA without conventional complex hybrid beamforming algorithms. In this paper, we divided the scenarios whether the channel state information of eavesdropper (CSIE) can be used at the transmitter, and proposed secrecy schemes for the both scenarios. We derived the optimal signal-artificial noise ratio by a line search algorithm. Additional analog beamforming algorithm is proposed for enhancing the secrecy performance using low-precision phase shifters. Simulation results show that the proposed scheme with LAA outperforms the hybrid beamforming scheme with uniform planar array (UPA). We also observed that the performance gap becomes larger, when the number of RF chains reducing.