Energy-Efficient NOMA Enabled Heterogeneous Cloud Radio Access Networks

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.