Pilot Power Control Combined with Greedy Pilot Assignment in Cell-Free Massive MIMO System

The cell-free massive multiple-input multiple-output (MIMO) system has a broad spectrum, but the pilot contamination in the pilot training phase seriously affects the performance of the system, so it is necessary to reduce the pilot contamination. In order to reduce pilot contamination, a pilot power control algorithm combined with greedy pilot assignment is proposed. First, greedy pilot assignment is performed. This stage improves the limited performance of lower-performance users. Then, on the basis of reasonable pilot assignment, the pilot power control is performed. This stage minimizes the maximum value of the normalized mean square error of all users. The two-stage joint pilot optimization improves the network throughput of the system. The simulation results show that the performance of the method proposed in the article is significantly better than the performance of the method of separately optimizing pilot allocation and pilot power proposed by current research.