Performance Analysis of Hybrid Beamforming Precoders for Multiuser Millimeter Wave NOMA Systems

This paper investigates the performance of hybrid beamforming (HBF) precoding techniques for multiuser millimeter-wave (mmWave) non-orthogonal multiple access (NOMA) systems under realistic propagation environments. Both fully connected structure (FCS) and sub-connected structure (SCS) HBF architectures are considered to analyze the trade-off between sum-rate performance and energy efficiency (EE). Low-complexity precoding schemes based on phased zero forcing (P-ZF) and successive interference cancellation aided zero forcing (SIC-ZF) are developed for FCS-HBF-NOMA and SCS-HBF-NOMA systems, respectively. The system performance is evaluated under line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios using the New York University (NYU) mmWave channel model. Results demonstrate that while FCS-HBF-NOMA achieves higher sum-rate due to its full beamforming gain, SCS-HBF-NOMA provides superior energy efficiency, particularly in high signal-to-noise ratio regimes. The impact of finite-resolution phase shifters is also examined, showing that low-bit quantization can achieve near-optimal performance with reduced power consumption. Furthermore, multistream transmission is explored to enhance spectral efficiency through spatial multiplexing. The effects of imperfect channel correlation and the number of users per cluster are analyzed, revealing critical design insights for practical mmWave NOMA systems. Overall, the proposed HBF-NOMA schemes offer an effective balance between performance, complexity, and energy efficiency for future wireless networks.

Keywords: Hybrid beamforming, millimeter-wave communications, non-orthogonal multiple access (NOMA), sub-connected structure, fully connected structure, energy efficiency, sum-rate optimization, successive interference cancellation, zero-forcing precoding, NYU mmWave channel model.