[Paper Review] A Survey of Downlink Non-orthogonal Multiple Access for 5G Wireless Communication Networks

Zhiqiang Wei, Jinhong Yuan+3 more|arXiv (Cornell University)|Sep 7, 2016

Advanced Wireless Communication Technologies57 references175 citations

TL;DR

This paper surveys downlink NOMA for 5G, detailing simple two-user SC-NOMA and general MC-NOMA, along with performance, resource allocation, and MIMO-NOMA, and outlines key features and challenges.

ABSTRACT

Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for the next generation cellular communication networks. In this paper, we first discuss a simple NOMA model with two users served by a single-carrier simultaneously to illustrate its basic principles. Then, a more general model with multicarrier serving an arbitrary number of users on each subcarrier is also discussed. An overview of existing works on performance analysis, resource allocation, and multiple-input multiple-output NOMA are summarized and discussed. Furthermore, we discuss the key features of NOMA and its potential research challenges.

Motivation & Objective

• Motivate the use of non-orthogonal multiple access (NOMA) to address 5G challenges such as massive connectivity, high spectral efficiency, and diverse QoS.
• Review basic two-user SC-NOMA and general multiuser MC-NOMA to illustrate principles and potential gains over OMA.
• Summarize existing performance analyses, resource allocation strategies, and MIMO-NOMA designs in the literature.
• Identify key features, advantages, and limitations of NOMA, and outline open research challenges for practical deployment.

Proposed method

• Present a simple two-user downlink SC-NOMA model with superposition transmission and SIC at receivers.
• Generalize to multiuser MC-NOMA with multiple users per subcarrier and power-domain sharing.
• Classify NOMA techniques into code-domain and power-domain multiplexer schemes, with emphasis on PDM-NOMA.
• Review performance analyses showing spectral efficiency and outage advantages over OMA, under various CSI assumptions.
• Survey resource allocation approaches for MC-NOMA, including joint power/subcarrier optimization and fairness considerations.
• Discuss MIMO-NOMA designs, including precoding/detection, user pairing, and beamforming aspects.

Experimental results

Research questions

• RQ1 What are the fundamental downlink NOMA schemes (SC-NOMA and MC-NOMA) and how do they compare to OMA?
• RQ2 What performance gains (spectral efficiency, fairness, latency) does NOMA offer under ideal and practical CSI assumptions?
• RQ3 What are the main resource allocation strategies for MC-NOMA and how do they balance sum rate and fairness?
• RQ4 How does MIMO-NOMA enhance performance and what design issues (precoding, user grouping) arise?
• RQ5 What are the key challenges and open research directions for practical NOMA deployment in 5G networks?

Key findings

• NOMA achieves higher spectral efficiency and improved user fairness compared to OMA.
• NOMA better exploits heterogeneous channel conditions, providing larger gains when channel differences are pronounced.
• NOMA supports more users per subcarrier, enabling massive connectivity and diverse QoS.
• CSI accuracy and SIC complexity are critical factors, impacting performance and practicality.
• Resource allocation for MC-NOMA is non-convex and challenging, with tradeoffs between sum rate and fairness.
• MIMO-NOMA offers additional gains through precoding and beamforming, but introduces design complexity and scheduling/optimization challenges.