Non-Orthogonal Multiple Access For Cooperative Communications: Challenges, Opportunities, And Trends

TL;DR

This paper reviews the current state of NOMA-based cooperative relay networks, discussing architectures, key features, and a hybrid power allocation strategy, while highlighting challenges and future research directions.

Contribution

It provides a comprehensive classification, comparison, and introduces a hybrid power allocation method for NOMA relay systems, along with insights into future research trends.

Findings

Hybrid power allocation reduces computational complexity

NOMA enhances spectral and energy efficiency

Identifies key challenges and opportunities in NOMA relay systems

Abstract

Non-orthogonal multiple access (NOMA) is a promising radio access technique for next-generation wireless networks. In this article, we investigate the NOMA-based cooperative relay network. We begin with an introduction of the existing relay-assisted NOMA systems by classifying them into three categories: uplink, downlink, and composite architectures. Then, we discuss their principles and key features, and provide a comprehensive comparison from the perspective of spectral efficiency, energy efficiency, and total transmit power. A novel strategy termed hybrid power allocation is further discussed for the composite architecture, which can reduce the computational complexity and signaling overhead at the expense of marginal sum rate degradation. Finally, major challenges, opportunities, and future research trends for the design of NOMA-based cooperative relay systems with other techniques are also highlighted to provide insights for researchers in this field.