Massive multiple-input multiple-output (MIMO) and non-orthogonal multiple access (NOMA) are two key techniques for enabling massive connectivity in future wireless networks. A massive MIMO-NOMA system can deliver remarkable spectral improvements and low communication latency. Nevertheless, the uncontrollable stochastic behavior of the wireless channels can still degrade its performance. In this context, the idea of an intelligent reflecting surface (IRS) has emerged as a promising technology for smartly overcoming the possibly detrimental effects of the wireless environment. The disruptive IRS concept of controlling the propagation channels via software can provide attractive performance gains to the communication networks, including higher data rates, improved user fairness, and possibly higher energy efficiency. In this article, we demonstrate the main roles of IRSs in MIMO-NOMA systems. Specifically, we identify key challenges and perform a comprehensive discussion of the main performance gains that can be achieved in IRS-assisted massive MIMO-NOMA (IRS-NOMA) networks. We outline exciting futuristic use case scenarios for IRS-NOMA and expose the main related challenges and future research directions. Furthermore, throughout the article, we support our in-depth discussions with representative numerical results.

中文翻译：

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智能反射面在多天线非正交多路访问中扮演什么角色？

大规模多输入多输出（MIMO）和非正交多址（NOMA）是在未来的无线网络中实现大规模连接的两项关键技术。大规模的MIMO-NOMA系统可以显着改善频谱并降低通信延迟。但是，无线通道的不可控制的随机行为仍会降低其性能。在这种情况下，智能反射面（IRS）的概念已成为一种有前途的技术，可以巧妙地克服无线环境的可能有害影响。通过软件控制传播信道的颠覆性IRS概念可以为通信网络提供诱人的性能提升，包括更高的数据速率，更高的用户公平性以及可能更高的能源效率。在这篇文章中，我们演示了IRS在MIMO-NOMA系统中的主要作用。具体而言，我们确定了关键挑战并全面讨论了在IRS辅助的大规模MIMO-NOMA（IRS-NOMA）网络中可以实现的主要性能提升。我们概述了IRS-NOMA令人兴奋的未来派用例场景，并揭示了主要的相关挑战和未来的研究方向。此外，在整篇文章中，我们以具有代表性的数值结果支持我们的深入讨论。