Design of hybrid beamforming considering beam squint in mmWave communication

Abstract

In this paper, we propose a beamforming design method to address the effect of beam squint effect, which is a problem that occurs when using a hybrid beamformer consisting of a digital beamformer and an analog beamformer in massive MIMO system. In mmWave communication, when a wideband signal is used in a massive MIMO system, a beam squint occurs in which a baseband signal arrives at different times for each antenna. In frequency domain, a steering vector is obtained as if a beam is formed at a different angle for each frequency, and if analog beamforming is performed in the direction of the actual beam, a distorted array gain is obtained. Conventional schemes for mitigating the beam squint have encountered challenges, such as high power consumption due to additional complex hardware or impractical computational complexity. To overcome the limitations, we propose a method to alleviate the beam squint effect by adding a variable to the existing narrowband hybrid beamforming structure in order to reduce hardware complexity and improve transmission rate at the same time. Specifically, our proposed scheme uses a variable ϵ to symmetrically move the beamforming frequency based on the center of the antenna, thereby minimizing the distortion of the array gain throughout the entire bandwidth in the frequency domain. Furthermore, the value of ϵ is expressed in a closed form based on the lower bound of achievable spectral efficiency, resulting in low complexity. Our simulation results show that the proposed scheme outperforms conventional hybrid beamformer and other techniques to deal with the beam squint.