Coordinated Multipoint Transmission in Downlink Multi-Cell NOMA Systems: Models and Spectral Efficiency Performance
We outline a general framework to use CoMP transmission technology in downlink multi-cell NOMA systems considering distributed power allocation at each cell. In this framework, CoMP transmission is used for users experiencing strong received signals from multiple cells, while each cell adopts NOMA for resource allocation to its active users. After a brief review of the working principles of different CoMP schemes, we investigate their applicability and necessary conditions for their use in a downlink multi-cell NOMA system. After that, we discuss various network scenarios with different spatial distributions of users and present the formula for achievable rate of users under each of the CoMP-NOMA scenarios. To this end, a numerical performance evaluation is carried out for the proposed CoMP-NOMA systems, and the results are compared with those for conventional orthogonal multiple access based CoMP systems. The numerical results quantify the spectral efficiency gain of the proposed CoMP-NOMA models over CoMP-OMA. Finally, we conclude this article by identifying the major challenges in implementing CoMP-NOMA in future cellular systems.