What Role Do Intelligent Reflecting Surfaces Play in Non-Orthogonal
Multiple Access?
Abstract
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 reduced communication
latency. Nevertheless, the uncontrollable stochastic behavior of the
wireless channels can still degrade its performance. In this context,
intelligent reflecting surface (IRS) has arisen as a promising
technology for smartly overcoming the harmful 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, in
contrast to the existing literature, we demonstrate the main roles of
IRSs in MIMO-NOMA systems. Specifically, we identify 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.