Code-aided non-orthogonal multiple access in downlink multiuser MIMO system

• Published in: Journal of the Franklin Institute Vol. 356; no. 12; pp. 6778 - 6792
• Main Author: Wu, Wei-Chiang
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01.08.2019; Elsevier Science Ltd
• Subjects: Algorithms; Antennas; Beamforming; Clustering; Computer simulation; Computer terminals; Data transmission; Electric noise; Interference; MIMO (control systems); Nonorthogonal multiple access
• ISSN: 0016-0032; 1879-2693; 0016-0032
• DOI: 10.1016/j.jfranklin.2019.06.003

Conventional downlink non-orthogonal multiple access (NOMA) uses the power domain for multiple access and applies successive interference cancellation (SIC) to mitigate intra-cluster interference. It requires sophisticated user terminals (UTs) clustering, moreover, imperfect SIC results in error propagation that severely degrades system capacity. In this paper, a novel code-aided multiuser multiple-input multiple-output NOMA (MIMONOMA) framework for downlink transmission is proposed. Since the total number of UTs in a cell is in general more than the number of transmit antennas at the base station (BS), purely zero-forcing (ZF) downlink beamforming is unable to mitigate multiuser interference (MUI). We first propose a simple grouping algorithm that separate all UTs in a cell into several clusters, with cluster number less than or equal to BS antennas. ZF-based multiuser beamforming is then employed to remove the inter-cluster interference. To mitigate the intra-cluster interference, we propose to modulate the downlink data for each UT within the same cluster by orthogonal codes, thereby, instead of SIC, matched-filtering can be employed at each UT for interference suppression. Computer simulation results quantify the capacity gain of the proposed coded-aided MIMONOMA method over conventional MIMONOMA schemes.