Sensitivity Analysis of mmWave Multiuser MIMO with Imperfect Analog Beamforming State Information

Abstract

In this paper we study analytically the sensitivity of analog-beamformed multiuser downlink MIMO systems to imperfect beamforming (BF) state information at the transmitter and the receiver. We consider different distributions of the transmit and receive BF errors and evaluate the end-to-end performance in terms of the statistical distribution of the minimum signal-to-interference plus noise ratio (SINR) and derive accordingly, for small fluctuation errors, analytical approximation of the average SINR and the corresponding symbol error probability (SEP). The analytical approximations of the SEPs are further benchmarked with the simulated error performance for both uncoded and coded transmission and for two BF architectures namely partially (PCA) and fully (FCA) connected architectures. Simulation results in line-of-sight propagation revealed that (i) tight estimates mainly of the transmit BF angles are required in the order of a fraction of one degree for moderate number of transmit antennas especially for FCA, and (ii) the BF accuracy requirement becomes stringent as the system load increases. We argue that with a moderate to high number of transmit antennas, multiuser beam alignment achieving sub-degree BF accuracy will be one of the main challenges of future mmWave communication systems that rely on analog BF.(1)