Channel Characteristic and Capacity Analysis of Millimeter Wave MIMO Beamforming System

Hybrid multiple input multiple output (MIMO) beamforming can be divided into shared and split MIMO beamforming architectures, according to different concatenations of radio frequency (RF) chains and antennas. This paper considers split MIMO beamforming for millimeter wave system, i.e., each antenna subarray is only connected with one RF chain. To obtain analog precoding matrix and combining matrix, an algorithm based on signal to leakage plus noise ratio (SLNR) is proposed to align the transmitter's and receiver's antenna subarrays in one- to-one way. The effectiveness of our proposed subarray alignment algorithm is validated by simulation, and the hybrid and purely digital beamforming are compared in terms of channel capacity. Numerical results show that for the number of transmit and receive antennas, the performance gap between purely digital and hybrid beamforming decreases by increasing the number of RF chains. Moreover, effective degree of freedom (EDOF) is introduced to analyze the channel characteristic.