A Matching-Based Pilot Assignment Algorithm for Cell-Free Massive MIMO Networks.

We propose a novel matching-based pilot assignment scheme to reduce the pilot contamination effect in cell-free massive multiple-input-multiple-output (MIMO) systems with low computational complexity. We use a many-to-many matching scheme to solve the AP selection problem so that the maximum number of UEs in a UE group equals the number of orthogonal pilots. Furthermore, orthogonal pilots are assigned to each UE group in descending order of the common serving AP ratio of UE groups. Simulation results demonstrate that the proposed algorithm achieves near-optimum performance and outperforms the existing pilot assignment schemes in terms of 95%-likely per-user throughput and computational complexity, especially in scenarios with a limited number of pilots.