Widely-Linear Hybrid Precoding for Millimeter Wave Massive MIMO System with IQ Imbalance

‍ ‍Based on the assumption of perfect hardware， the hybrid precoding of millimeter-wave massive MIMO （Multiple-Input Multiple-Output） system has been extensively studied. However， the radio frequency distortion caused by the non-ideal characteristics of the hardware in millimeter-wave band tends to severely restrict the performance of the system. This paper considered the non-ideal characteristics of in-phase （I） branch and quadrature （Q） branch imbalance at the transmitter in millimeter-wave massive MIMO system， and designed a hybrid precoding scheme based on a widely-linear real-valued signal model to suppress the impact of IQ imbalance on system performance. Complex-real transformation was utilized to transform the received signal model containing conjugate interference caused by IQ imbalance into a widely linear real-valued signal model. Based on the Orthogonal Matching Pursuit （OMP） algorithm， the analog precoder and digital precoder were designed iteratively in the complex and real domains respectively. The simulation results show that the proposed scheme can effectively improve spectral efficiency and bit error rate performance.