毫米波无线通信系统混合波束成形综述

毫米波频段拥有大量未充分使用的频谱资源，能有效缓解低频段频谱拥塞，并且由于毫米波波长较短，能极大地减小大规模天线系统的物理尺寸，使得毫米波通信成为5 G无线通信系统潜在的关键技术之一。考虑到毫米波传播路径损耗严重，毫米波系统需采用波束成形技术改善传输质量。在毫米波大规模多输入多输出(Multiple-input multiple-out, MIMO)系统中，由于数字波束成形高功耗、高成本问题，混合数模波束成形成为重要的替代方案。本文首先阐述了毫米波混合波束成形的研究现状，而后给出了系统模型，最后介绍了信道估计、码本设计和低复杂度设计等混合波束成形的关键技术。

Overview of Hybrid Beamforming for Millimeter Wave Systems

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.