Key points are not available for this paper at this time.
Heterogeneous ultra dense networks (HUDNs) and non-orthogonal multiple access (NOMA) have been identified as two proposing techniques for 5G mobile communication systems due to their great capabilities to enhance spectrum efficiency. This article investigates the application of NOMA techniques in HUDNs to support massive connectivity in 5G systems. In particular, a unified NOMA framework is proposed, including power-domain NOMA and code-domain NOMA, which can be configured flexibly to serve different application scenarios. As a further advance, unified NOMA framework enabled HUDNs are further investigated, with particular focus on user association and resource allocation. Two case studies are provided for demonstrating the effectiveness of unified NOMA enabled HUDNs. Finally, some main challenges and promising research directions in NOMA enabled HUDNs are identified.
Qin et al. (Fri,) studied this question.