Joint Power Allocation and Decoding Order Selection for NOMA Systems: Outage-Optimal Strategies

TL;DR

This paper proposes novel joint power allocation and decoding order strategies for NOMA systems that optimize outage performance without requiring full CSI, outperforming existing methods especially at high SNR.

Contribution

It introduces two outage-optimal PA-DOS strategies that adapt to user priorities and target rates, reducing outage probabilities with minimal CSI feedback.

Findings

Strategies outperform existing methods in outage performance.

Optimal strategies do not always require full CSI.

High-SNR regimes allow near-optimal user outage probabilities.

Abstract

We investigate joint power allocation and decoding order selection (PA-DOS) aimed at enhancing the outage performance of non-orthogonal multiple access (NOMA) systems. By considering the diverse target rates of users, new important properties of NOMA are revealed: When users' target rates satisfy certain conditions, the channel state information (CSI) is not required by PA-DOS to minimize the system outage probability, and different users' outage probabilities can be minimized simultaneously; When such conditions are not satisfied, the opposite situation occurs. Following these properties, two PA-DOS strategies are designed regarding distinct user priorities, which ensure the minimization of the system outage probability and the user outage probability of the high-priority user. Especially, these strategies do not require CSI or only require one-bit CSI feedback depending on users' target rates. Analytical and numerical results are provided to demonstrate that the proposed strategies significantly outperform the existing strategies in terms of both system and user outage performance. Furthermore, the results show that although under some target rates the minimum user outage probabilities cannot be simultaneously achieved, they can be closely approached at the same time in the high-signal-to-noise-ratio regime by the proposed strategies.