Energy-Efficient Hybrid Beamforming Design for Wideband Terahertz Ultra-Massive MIMO Systems

Ultra-massive multiple-input multiple-output (UM-MIMO) has been considered as one of the promising technologies for terahertz (THz) wireless communications to compensate for the severe path loss. However, the widely acknowledged hybrid beamforming approaches in massive MIMO cannot deal with the beam split effect caused by the increased scale of array dimension and system bandwidth in THz UM-MIMO systems. In this paper, the hybrid beamforming specifically designed for wideband THz UM-MIMO systems with the beam split effect is proposed. Firstly, a novel technique of hybrid beamforming is formulated as a sub-beam coherent combination method to cover the dispersed spatial directions. Subsequently, the dynamic hybrid hardware architecture is considered to flexibly adapt to various beam splits on different path directions, in which the optimal number of the activated subarray is elaborately designed to alleviate beam split while reducing power consumption. Simulation results indicate that our scheme achieves desirable beamforming gain distribution across the entire bandwidth, as well as achieving higher energy efficiency than other fixed hybrid hardware architectures designed for alleviating the beam split effect.