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

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 $N_{s}$ 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.

Keywords

• Fully connected structure
• millimeter-wave
• multistream hybrid beamforming
• NOMA
• sub-connected structure
• sum-rate maximization