Power Normalization and Precoding for Massive MIMO in Outdoor-to-Indoor mmWave Relaying

In this paper, we investigate two millimeter waves (mmWave) relaying scenarios to assist outdoor-to-indoor communications, where indoor multi-users are served by an outdoor base station (BS) in urban cellular networks. Considering a two-hop full-duplex (FD) relaying scheme, we first propose a scheme where the BS performs zero-forcing (ZF) precoding based on the end-to-end channel response. In this case, the relay normalizes, amplifies, and forwards the signals to the indoor users. Second, we assume that the BS performs a precoding based on the first hop channel response only. The relay, in this second scheme, normalizes, precodes (using the second hop channel response), amplifies, and forwards the signals. The transmission in both schemes is enabled by massive multiple-input multiple-output (mMIMO). We derive the expressions of the average signal-to-noise ratio (SNR) for each scenario, and quantity the asymptotic SNR. Outage probability, for which we derive closed-form expressions, in addition to capacity, and energy-efficiency, are used to evaluate the two scenarios, and Monte Carlo simulation results are added to assess the accuracy of our analysis. Finally, the two schemes are compared taking into consideration the precoding complexity, the number of antennas, as well as the number of users. Practical recommendations are formulated at the end of the analysis.