Secrecy Rates of Relay-Assisted Massive MIMO Downlink with Hybrid Precoding

Abstract

In this paper, the achievable secrecy rates are derived for the relay-assisted massive multiple-input multiple-output (MIMO) downlink with limited number of radio frequency (RF) chains at the base-station (BS). Two hybrid precoder designs are investigated for the dual-hop transmission of information and artificial noise. Two channel estimation techniques are proposed. Thereby, the achievable secrecy rate gap between the hybrid precoding and full-dimensional digital precoding is quantified for imperfect channel state information. Our analysis reveals that the proposed hybrid precoders can significantly reduce the number of RF chains at the BS, while yielding only a marginal percentage loss of the achievable secrecy rate compared to the full-dimensional digital precoders. Hence, the proposed hybrid precoding can be used for provisioning physical layer security in relay-aided massive MIMO downlink with a lower computational/implementation complexity.