The integration of intelligent reflecting surface (IRS) to multiple access networks is a cost-effective solution for boosting spectrum/energy efficiency and enlarging network coverage/connections. However, due to the new capability of IRS in reconfiguring the wireless propagation channels, it is fundamentally unknown which multiple access scheme is superior in the IRS-assisted wireless network. In this letter, we pursue a theoretical performance comparison between non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) in the IRS-assisted downlink communication, for which the transmit power minimization problems are formulated under the discrete unit-modulus reflection constraint on each IRS element. We analyze the minimum transmit powers required by different multiple access schemes and compare them numerically, which turn out to not fully comply with the stereotyped superiority of NOMA over OMA in conventional systems without IRS. Moreover, to avoid the exponential complexity of the brute-force search for the optimal discrete IRS phase shifts, we propose a low-complexity solution to achieve near-optimal performance.

中文翻译：

---

具有用户配对的智能反射表面辅助多路访问：NOMA 还是 OMA？

将智能反射面 (IRS) 集成到多个接入网络是提高频谱/能源效率和扩大网络覆盖/连接的经济高效的解决方案。然而，由于IRS在重新配置无线传播信道方面的新能力，在IRS辅助的无线网络中哪种多址接入方案更优越是根本未知的。在这封信中，我们对 IRS 辅助下行链路通信中非正交多址 (NOMA) 和正交多址 (OMA) 之间的理论性能进行了比较，为此在离散单位模反射下制定了发射功率最小化问题对每个 IRS 元素的约束。我们分析了不同多址接入方案所需的最小发射功率，并进行数值比较，结果证明，在没有 IRS 的传统系统中，NOMA 优于 OMA 的刻板印象并不完全符合。此外，为了避免对最佳离散 IRS 相移进行强力搜索的指数复杂性，我们提出了一种低复杂性的解决方案来实现接近最佳的性能。