Research on user grouping and AP selection in the uplink of cell-free massive MIMO-NOMA

Focusing on the problems of user grouping and AP selection in the uplink of cell-free massive MIMO-NOMA system, a maximum channel correlation user grouping scheme and an AP selection scheme based on effective channel gain are proposed. Firstly, the maximum channel correlation user grouping scheme calculates the effective channel gain difference and channel linear correlation between any two users through statistics and the Pearson correlation coefficient. Then, users are grouped to minimize the difference between any two users. Based on the user grouping results, users are first sorted according to user channel quality, and then connectable APs are selected for each user based on effective channel gain. Experimental results show that the user grouping scheme based on maximum channel correlation can reduce the interference level among multiple users and significantly improve the sum spectrum efficiency of the system and the fairness of communication. At the same time, the AP selection scheme based on effective channel gain can reduce interference between users and reduce the complexity of system calculations, effectively improving the sum spectrum efficiency of the system.