Coordinated Multi-Point (CoMP) Transmission in Downlink Multi-cell NOMA Systems: Models and Spectral Efficiency Performance

We outline a general framework to use coordinated multi-point (CoMP) transmission technology in downlink multicell non-orthogonal multiple access (NOMA) systems considering distributed power allocation at each cell. In this framework, CoMP transmission is used for users experiencing strong receivesignals 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 identify their applicability and necessary conditions for their use in downlink multi-cell NOMA system. After that, we discuss different network scenarios with different spatial distributions of users and study the applicability of CoMP schemes in these network scenarios. To the 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 (OMA)-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 potential major challenges in implementing CoMP-NOMA in future cellular systems.