Dense Distributed Massive MIMO: Precoding and Power Control

We present a non-iterative downlink precoding approach for distributed massive multiple-input multiple output systems (DmMIMO) where users are served by overlapping clusters of transmission/reception points (TRP) and channel estimates for links outside the clusters are available. In contrast to traditional cellular systems, each user is served by its own cluster of transmission points and a DmMIMO TRP could be part of multiple clusters. We also propose a power control algorithm that ensures per site power constraints are satisfied when the proposed precoding approach is used. The algorithm extends straightforwardly to the multiple receive antenna case. Extensive simulation results are presented for various cluster sizes and inter-site distances for a dense urban environment with channels generated using ray tracing. Results show that spectral efficiency comparable to massive MIMO can be achieved for a dense deployment of small cells each with only a small number of antennas with our DmMIMO scheme without the need for extensive coordination between many access points.