Hybrid Beamformer Exploiting Multistream per User Transmission for Millimeter-Wave NOMA Communications

Abdulahi Abiodun Badrudeen,Seunghwan Won,Chee Yen Leow

doi:10.1109/access.2022.3152537

Abstract

This treatise investigates multistream hybrid beamforming (HBF) for a millimeter-wave non-orthogonal multiple access (NOMA) system deployed in a downlink of an urban microcell environment. Maximization problem is developed to optimize sum-rate. For the sake of ensuring high correlation of users’ channels, user’s clustering and ordering are based on the angle of arrivals and users’ channel-weights, respectively. An optimized analog combiner of each user is obtained from the first <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{s}$ </tex-math></inline-formula> column vectors of the left unitary matrix derived from the singular value decomposition of the channel of each user. Analog beamformer is matched to the phase of the strong users ’ composite intermediate analog channel to maximize the beamforming gain. Both the analog combiner and precoder for sub-connected structure (SCS) are formulated via a novel dominant sub-array matrix elements’ extractor. Conventional zero-forcing processing is contemplated for digital precoding. Memory space complexity is evaluated to corroborate the simplicity of the proposed schemes’ computational complexity. Results obtained from the simulation exhibit that HBF-NOMA attain superior sum-rate than HBF-orthogonal multiple access and conventional multiuser schemes in line of sight link. Lastly, the proposed SCS-HBF-NOMA precoding scheme performs higher than fully connected counterpart in terms of energy efficiency.

Highlights

Rapid demands for high data-rate mobile wireless applications such as online gaming, telemedicine, electronic learning, and video conferencing result in a bottleneck for deploying below 6 [GHz] spectrum owing to the inherently scarce signal bandwidth limitation
We focus more on line of sight (LOS) link because in case of small cell configuration, mmW signal travels by LOS [21], which favors the exploitation of non-orthogonal multiple access (NOMA) communications
The significant contributions of this treatise are recapitulated as follows: 1) We develop a multistream fully connected hybrid beamforming (HBF) structure articulating an explicit relationship between each RF chain at the output of digital beamformer (DB) and the corresponding antennas via analog beamformer (AB) components

Summary

Introduction

Rapid demands for high data-rate mobile wireless applications such as online gaming, telemedicine, electronic learning, and video conferencing result in a bottleneck for deploying below 6 [GHz] spectrum owing to the inherently scarce signal bandwidth limitation. A paradigm shift from the current existing spectrum band to a millimeter-wave (mmW) one ranging from 30 [GHz] to 300 [GHz] is inevitable to support high data rate traffic in order of Gbps for the post-5G wireless communications. The small wavelength of mmW allowing the exploitation of a large number of antennas in a small area of wireless device circuit is to combat the effect of path loss fading. Deploying massive antennas for multiple input multiple output (MIMO). Hybrid (digital and analog) beamforming (HBF) has been proposed as an appropriate beamforming (BF) approach for massive MIMO

Methods

Results

Conclusion