Distributed and Centralized Subcarrier-based Precoding for Cell-Free Massive MIMO Networks

Cell-Free Massive MIMO is a distributed Massive MIMO network, consisting of many low-cost, low-energy access points (APs) connected to a Central Control Unit (CCU) via a backhaul network. The number of AP antennas far surpasses the number of users. In CFmM, the network is not divided into cells, and all APs cover all users. Although distributing the APs enhances network coverage and efficiency, it significantly increases the backhaul network load which is a drawback for future networks and the emerging C-RAN with limited backhaul capacity. In this paper, we propose centralized and distributed subcarrier-based zero-forcing (ZF) precoding solutions and compute the downlink rate for the proposed systems. The centralized solution resolves the need for using multiple antennas per AP whereas, the distributed version is a suitable candidate to reduce the backhaul load.