Cooperative NOMA-Based User Pairing for URLLC: A Max-Min Fairness Approach

TL;DR

This paper proposes a cooperative NOMA user pairing scheme with resource allocation to maximize fair throughput in URLLC, demonstrating significant improvements over traditional NOMA and OMA methods through numerical analysis.

Contribution

It introduces a novel cooperative NOMA user pairing and resource allocation method optimized for max-min fairness in short packet communications.

Findings

Significant fair throughput improvement over NOMA and OMA.

Proposed suboptimal algorithms converge to near-optimal solutions.

Enhanced fairness with slight trade-offs in average throughput.

Abstract

In this paper, cooperative non-orthogonal multiple access (C-NOMA) is considered in short packet communications with finite blocklength (FBL) codes. The performance of a decode-and-forward (DF) relaying along with selection combining (SC) and maximum ratio combining (MRC) strategies at the receiver side is examined. We explore joint user pairing and resource allocation to maximize fair throughput in a downlink (DL) scenario. In each pair, the user with a stronger channel (strong user) acts as a relay for the other one (weak user), and optimal power and blocklength are allocated to achieve max-min throughput. To this end, first, only one pair is considered, and optimal resource allocation is explored. Also, a suboptimal algorithm is suggested, which converges to a near-optimal solution. Finally, the problem is extended to a general scenario, and a suboptimal C-NOMA-based user pairing is proposed. Numerical results show that the proposed C-NOMA scheme in both SC and MRC strategies significantly improves the users' fair throughput compared to the NOMA and OMA. It is also investigated that the proposed pairing scheme based on C-NOMA outperforms the Hybrid NOMA/OMA scheme from the average throughput perspective, while the fairness index degrades slightly.