Analog Beamsteering for Flexible Hybrid Beamforming Design in Mmwave Communications

TL;DR

This paper introduces an analog beamsteering method for hybrid beamforming in mmWave communications that approaches digital beamforming performance, analyzing the impact of practical codebook limitations and enabling flexible, environment-adaptive architectures.

Contribution

It proposes a novel analog beamsteering approach that closely matches digital beamforming performance and provides a closed-form analysis of codebook size effects on rate loss.

Findings

Analog beamsteering achieves near-SVD digital beamforming performance at low to medium SNR.

A closed-form expression relates rate loss to codebook size, antennas, and SNR.

Codebook size should exceed the number of antennas for optimal performance.

Abstract

In this paper, we propose an analog beamsteering approach for enabling flexible hybrid beamforming design that can achieve performance close to singular value decomposition (SVD) based digital beamforming with single user case. As a starting point, assuming the use of a codebook with infinite precision, we apply transposes of antenna array response matrices as analog beam-formers at the BS and the UE sides. The resulting effective chan-nel matrix including both propagation channel and analog beam-formers is shown to be able to provide a maximal achievable rate very close to SVD based digital beamforming at low to medium SNR. Next, the impact of a finite size codebook is analyzed for practical analog beamformer design. A closed-form derivation is obtained for mapping rate loss to the number of antennas, code-book sizes and the received SNR. The analysis shows that in or-der to achieve performance comparable to analog beamforming with infinite precision, the codebook size should be at least larger than the number of implemented antennas. Therefore, the pro-posed analog beamforming approach can be designed inde-pendently without taking digital beamforming into account. Such an approach can lead to the development of flexible hybrid beam-forming architectures that could adapt to a changing propagation environment via agile analog beam selection and maximize spatial multiplexing gain via proper digital beamformer design.