Secure Hybrid Analog and Digital Precoding for Massive MIMO Systems

Hybrid analog and digital precoding is one of the key techniques for reducing the number of radio frequency (RF) chains in massive multiple-input multiple-output (MIMO) systems. However, the security of transmission, as well as the interference among multiple users should be both considered for such a system. In this paper, we introduce the idea of spare beams to design the analog precoder for eliminating the multi-user interference. Meanwhile, for enhancing the security, the digital precoder is designed with the aid of artificial noise (AN). Simulation results demonstrate that the proposed scheme has the advantage of achieving better sum rate in comparison to the traditional scheme, while improving the secrecy rate with the identical number of sparse RF chains.