Spectral Efficiency Optimization in Cell-Free Massive MIMO with UAV Cooperation

For the pilot contamination issue caused by interference between ground and aerial users in cell-free massive MIMO networks with UAV-assisted communication, a bidirectional clustering pilot assignment algorithm based on matching coefficients is proposed (BCG). First, utilizing the position information of access points (APs) and users, users are grouped through bidirectional clustering with a cap on per-group users to eliminate intra-group contamination. Next, to minimize inter-group pilot contamination, we compute the matching coefficient between users sharing the same orthogonal pilot and their corresponding serving APs based on the distance between them. Match users with each other and assign pilots, ensuring that pilot contamination among users from different groups sharing the same orthogonal pilot remains at a relatively low level. Finally, The proposed scheme exhibits significant improvements, as evidenced by simulation data. The Bidirectional clustering pilot allocation algorithm based on matching coefficient reduces pilot contamination and significantly improves the spectral efficiency of the uplink system.