A Novel Spectrally-Efficient Uplink Hybrid-Domain NOMA System

TL;DR

This paper introduces a hybrid-domain NOMA system that combines code-domain and power-domain techniques to support more uplink users, optimizing spectral efficiency through iterative algorithms and outperforming conventional schemes.

Contribution

The paper presents a novel hybrid-domain NOMA approach that enhances uplink user capacity and spectral efficiency by combining decoding strategies and advanced optimization techniques.

Findings

HD-NOMA supports more uplink users than SCMA.

The proposed optimization improves spectral efficiency.

Numerical results demonstrate superior performance of HD-NOMA.

Abstract

This paper proposes a novel hybrid-domain (HD) non-orthogonal multiple access (NOMA) approach to support a larger number of uplink users than the recently proposed code-domain NOMA approach, i.e., sparse code multiple access (SCMA). HD-NOMA combines the code-domain and power-domain NOMA schemes by clustering the users in small path loss (strong) and large path loss (weak) groups. The two groups are decoded using successive interference cancellation while within the group users are decoded using the message passing algorithm. To further improve the performance of the system, a spectral-efficiency maximization problem is formulated under a user quality-of-service constraint, which dynamically assigns power and subcarrier to the users. The problem is non-convex and has sparsity constraints. The alternating optimization procedure is used to solve it iteratively. We apply successive convex approximation and reweighted $\ell_1$ minimization approaches to deal with the non-convexity and sparsity constraints, respectively. The performance of the proposed HD-NOMA is evaluated and compared with the conventional SCMA scheme through numerical simulation. The results show the potential of HD-NOMA in increasing the number of uplink users.