Graph Partitioning Based Pilot Assignment for Scalable Cell-Free Massive MIMO Systems

This letter focuses on the pilot assignment problem in scalable cell-free systems and proposes a graph partitioning based scheme to improve the user fairness. Specifically, a novel metric to indicate the strength of potential pilot contamination between any two users is firstly defined, and a weighted graph is constructed by taking the novel defined metric as the edge weight to describe the potential interference among users. Then, we formulate the pilot assignment as a graph partitioning problem, and get the solution by the proposed degree sorting-based algorithm. Simulation results verify the effectiveness of the constructed metric to indicate the pilot contamination between users and the fairness advantage of the proposed algorithm.