NOMA-Based Cell-Free Massive MIMO Over Spatially Correlated Rician Fading Channels

This paper considers non-orthogonal multiple access (NOMA) based cell-free massive multiple-input multiple-output (mMIMO) systems over spatially correlated Rician fading channels. Closed-form downlink achievable sum-rate expression is derived by taking into account spatial correlation among multi-antenna access points, inter-cluster interference, intra-cluster pilot contamination, and imperfect successive interference cancellation (SIC). In particular, we propose an intra-cluster power allocation design for improving the system performance. Furthermore, we investigate the downlink performance with both minimum mean-squared error (MMSE) and element-wise MMSE channel estimation. It is interesting to find out that the correlation magnitude has a negligible effect on the system sum-rate in spatially correlated Rician fading channels. The numerical results validate the correctness of the presented results and confirm the effectiveness of the proposed power allocation.