H-CRANs are envisioned to be promising in 5G wireless networks. H-CRANs enable users to enjoy diverse services with high energy efficiency, high spectral efficiency, and low-cost operation, which are achieved by using cloud computing and virtualization technologies. However, H-CRANs face many technical challenges due to massive user connectivity, increasingly severe spectrum scarcity, and high penetration of energy-constrained devices. These challenges may significantly degrade network performance and user quality of service if not properly tackled. NOMA schemes exploit non-orthogonal resource sharing among multiple users and have received tremendous attention due to their great potential to improve spectral and energy efficiency in 5G networks. This article focuses on the energy efficiency study in a NOMA enabled H-CRAN. Key 5G technologies that can be applied in NOMA H-CRANs to improve energy efficiency are presented. Challenges to implement these technologies and open research issues are discussed. The performance study shows that using NOMA enabled H-CRANs together with the key presented technologies can greatly improve overall system energy efficiency.

中文翻译：

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高能效的NOMA异构云无线电接入网络

预计H-CRAN在5G无线网络中很有前途。通过使用云计算和虚拟化技术，H-CRAN使用户能够享受高能效，高频谱效率和低成本运营的多样化服务。但是，由于大规模的用户连接，日益严重的频谱稀缺以及能量受限设备的高普及率，H-CRAN面临许多技术挑战。如果处理不当，这些挑战可能会严重降低网络性能和用户服务质量。NOMA方案利用了多个用户之间的非正交资源共享，并因其在5G网络中提高频谱和能效的巨大潜力而​​受到了极大的关注。本文重点介绍启用NOMA的H-CRAN中的能效研究。提出了可用于NOMA H-CRAN以提高能源效率的关键5G技术。讨论了实施这些技术和开放研究问题的挑战。性能研究表明，将启用了NOMA的H-CRAN与所展示的关键技术一起使用可以大大提高整体系统的能效。