Effects of Mutual Coupling on Lattice Reduction-Aided Millimeter Wave Hybrid Beamforming

Abstract

Millimeter wave (mmWave) communications has gained considerable attention due to the availability of large bandwidths, which can be harnessed to meet the ever-increasing data rate demands. Directional beamforming combined with baseband precoding should be used owing to the high propagation losses encountered at mmWave frequencies. This is typically referred to as hybrid beamforming. In hybrid beamforming arrangements, the adjacent antenna elements are closely spaced, typically at half-wavelength spacing in order to compensate for the propagation losses. In this antenna array configuration, the mutual coupling between the adjacent antenna elements becomes significant and may limit the performance of the system. Therefore, in this paper, we propose a reduced-complexity near-optimal detection scheme, namely the so-called Element-based Lattice Reduction algorithm, for hybrid beamforming in mmWave communications and we investigate its performance in the presence of mutual coupling. We demonstrate that the mutual coupling affects the spatial correlation of the channels between the different antennas depending on the distance between the antenna elements, which has a direct effect on the achievable rate as well as bit error ratio (BER) performance of the system.