Intelligent Reflecting Surface-Assisted Multiple Access With User Pairing: NOMA or OMA?
Intelligent Reflecting Surface-Assisted Multiple Access With User Pairing: NOMA or OMA?
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DOI：
10.1109/lcomm.2020.2969870
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发表时间：
2020-01
期刊：
影响因子：
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通讯作者：
Beixiong Zheng;Qingqing Wu;Rui Zhang
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文献类型：
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作者：
Beixiong Zheng;Qingqing Wu;Rui Zhang
将智能反射面 (IRS) 集成到多个接入网络是一种经济有效的解决方案，可提高频谱/能源效率并扩大网络覆盖范围/连接。然而，由于IRS在重新配置无线传播信道方面的新能力，根本不知道哪种多址方案在IRS辅助的无线网络中更优越。在这封信中，我们对IRS辅助下行链路通信中的非正交多址（NOMA）和正交多址（OMA）进行了理论性能比较，其中在每个IRS元件上的离散单位模反射约束下制定了发射功率最小化问题。我们分析了不同多址接入方案所需的最小发射功率，并进行了数值比较，结果并不完全符合在没有 IRS 的传统系统中 NOMA 相对于 OMA 的刻板印象。此外，为了避免强力搜索最佳离散 IRS 相移的指数复杂性，我们提出了一种低复杂性解决方案来实现接近最佳的性能。
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.