Abstract:The large underutilized spectrum of Millimeter wave (mmWave) can efficiently alleviate the spectrum shortage at lower frequency bands, and the physical size of large-scale antennas systems can be greatly reduced due to the shorter wavelength at mmWave frequencies, which enables mmWave communication to be one of the potentially crucial techniques for 5 G wireless communication systems. Considering the severe path loss of mmWave frequencies, beamforming needs to be utilized in an mmWave system for improving the transmission quality. Due to the high power consumption and high cost of fully digital beamforming methods in mmWave massive MIMO systems, hybrid digital and analog beamforming become an important alternative scheme. Here, we first introduce the current research state of hybrid beamforming schemes for mmWave MIMO systems. Then the system model is built. Finally, the crucial technologies of hybrid beamforming,i.e., channel estimation, codebook design and low-complexity design are described.