Enhanced User Grouping and Power Allocation for Hybrid mmWave MIMO-NOMA Systems

• Published in: IEEE transactions on wireless communications Vol. 21; no. 3; pp. 2034 - 2050
• Main Authors: Zhu, Jinle, Li, Qiang, Liu, Zilong, Chen, Hongyang, Poor, H. Vincent
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Array signal processing; beam selection; Beamforming; Clustering algorithms; Complexity; Complexity theory; Hybrid systems; Linear programming; Millimeter waves; MIMO; MIMO communication; Mixed integer; mmWave; Nesting; NOMA; Nonlinear programming; Nonorthogonal multiple access; Optimization; power allocation; Resource management; Uplink; user grouping
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2021.3109053

Non-orthogonal multiple access (NOMA) and millimeter wave (mmWave) are two key enabling technologies for the fifth-generation (5G) mobile networks and beyond. In this paper, we consider uplink communications with a hybrid beamforming structure and focus on improving the spectral efficiency (SE) and energy efficiency (EE) of mmWave multiple-input multiple-output (MIMO)-NOMA systems with enhanced user grouping and power allocation. It is noted that the optimization of the SE/EE is a challenging task due to the non-linear programming nature of the corresponding problem involving user grouping, beam selection, and power allocation. Our idea is to decompose the overall optimization problem into a mixed integer problem comprised of user grouping and beam selection only, followed by a continuous problem involving power allocation and digital beamforming design. Exploiting the directionality property of mmWave channels, we first propose a novel initial agglomerative nesting (AGNES) based user grouping algorithm by taking advantage of the channel correlations. To avoid the prohibitively high complexity of the brute-force search approach and to address the overlapping beam problem, we propose two suboptimal low-complexity user grouping and beam selection schemes, the two-stage direct AGNES (D-AGNES) scheme and the joint successive AGNES (S-AGNES) scheme. We also introduce the quadratic transform (QT) to recast the non-convex power allocation optimization problem into a convex one subject to a minimum required data rate of each user. The continuous problem is solved by iteratively optimizing the power and the digital beamforming. Extensive simulation results have shown that our proposed mmWave-NOMA design outperforms the conventional orthogonal multiple access (OMA) scenario and the state-of-art NOMA schemes.