Study of Clustering Solutions for Scalable Cell-Free Massive MIMO

In response to the requirements of 5G and beyond, cell-free systems have emerged to ensure uniform service throughout the area. However, the idea of having no cells leads to a considerably large monolithic system, which is not scalable. In this context, common sense suggests the creation of clusters of Access Points (APs) and User Equipments (UEs) that allow the system to be managed locally to some extent. The clustering procedure has to ensure certain performance for the global system and, at the same time, ensure its scalability. In this paper, first, scalability is analyzed. Subsequently, we study and compare two clustering approaches for uplink and downlink. Finally, we propose a combination of clustering and resource allocation techniques that outperforms the rest of the analyzed state-of-the-art solutions.