Distributed Precoding Design for Cell-Free Massive MIMO Systems

We propose a distributed precoding design for downlink cell-free massive multiple-input multiple-output (MIMO) where the channel state information (CSI) exchange among the base stations (BSs) via backhaul signaling is entirely replaced by a novel over-the-air (OTA) signaling mechanism. The proposed method enjoys desirable flexibility and scalability properties, as the amount of OTA signaling does not scale with the number of BSs or user equipments. Numerical results show remarkable gains over uncoordinated precoding design, even after very few iterations. The proposed method may also outperform the centralized precoding design under realistic CSI acquisition.