Cell-free massive MIMO systems utilizing multi-antenna access points

Cell-free massive multiple-input multiple-output (MIMO) was recently proposed as an alternative to partitioning coverage area into cells. The main idea is to have many access points (APs) distributed over the coverage area to serve a smaller number of users. Users are served by all APs simultaneously by sharing time and frequency resources. In this paper, we study the deployment of multi-antenna APs in cell-free massive MIMO systems. In particular, we study the advantages and disadvantages of using multi-antenna APs with respect to the achievable rates, the backhauling traffic, and the infrastructure cost to give results on how disperse antennas should be among APs.