Scalable and Distributed MMSE Algorithms for Uplink Receive Combining in Cell-Free Massive MIMO Systems

In cell-free Massive MIMO systems, a large number of distributed wireless access points (AP) are simultaneously serving a number of user equipments (UEs). This setup has the ability to offer a good quality of service, be it that there is still a need for low-complexity signal processing algorithms. In this paper, the problem of optimal uplink receive combining is tackled by providing an efficient distributed MMSE algorithm, with a minimal number of exchanged parameters between the APs and the network center. Scalable versions of this distributed MMSE algorithm are also proposed ensuring that the algorithm can be used in large networks with many UEs.