Comparative Performance Analysis of Pilot Allocation Techniques in Massive Cell-Free MIMO Systems

In this paper, we investigate various pilot allocation methods in cell-free massive MIMO (CF MIMO) systems. In these systems, multiple distributed access points (APs) provide services to users, and optimal pilot allocation is crucial to enhancing system performance. Improper pilot allocation can lead to pilot contamination and reduced spectral efficiency (SE), so several methods for mitigating interference are explored. This study implements and simulates multiple allocation strategies, including random allocation, greedy, graph coloring, user grouping, and interference-aware user grouping (IA-UG). The simulation results indicate that more advanced methods, such as graph coloring and IA-UG, provide higher spectral efficiency, while simpler methods like random and greedy allocation are better suited for systems with lower user density. These findings can help design more optimal CF MIMO systems and provide a solution to reduce pilot contamination in large-scale networks.