Performance Evaluation of Beam Shapes in a Two-Step-Precoded Massive MIMO System

Jumpei YAMAMOTO  Toshihiko NISHIMURA  Takeo OHGANE  Yasutaka OGAWA  Daiki TAKEDA  Yoshihisa KISHIYAMA  

IEICE TRANSACTIONS on Communications   Vol.E103-B   No.6   pp.703-711
Publication Date: 2020/06/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2018EBP3271
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
5G,  massive MIMO,  higher frequency band,  two-step beamforming,  

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Massive MIMO is known as a promising technology for multiuser multiplexing in the fifth generation mobile communication system to accommodate the rapidly-increasing traffic. It has a large number of antenna elements and thus provides very sharp beams. As seen in hybrid beamforming, there have already been many papers on the concatenation of two precoders (beamformers). The inner precoder, i.e., a multi-beam former, performs a linear transformation between the element space and the beam space. The outer precoder forms nulls in the limited beam space spanned by selected beams to suppress the inter-user interference. In this two-step precoder, the beam shape is expected to determine the system performance. In this paper, we evaluate the achievable throughput performance for different beam-shaping schemes: a discrete Fourier transform (DFT) beam, Chebyshev weighted beams, and Taylor weighted beam. Simulations show that the DFT beam provides the best performance except the case of imperfect precoding and cell edge SNR of 30dB.