Distributed Beamforming for Macro Diversity and Power Control With Large Arrays in Spatial Correlated Channels

Downlink beamforming plays a key role in massive multiple-input multiple-output (MIMO) systems to provide reasonable signal-to-interference-plus-noise ratio (SINR) in the presence of intercell interference (ICI). Due to an excessive backhaul overhead, limited cooperative beamforming is usually desirable. In this paper, we consider distributed beamforming that can exploit macro diversity with limited cooperation for cell-edge users where multiple base stations (BSs) transmit signals to those users simultaneously. Bounds on the SINRs are derived to see the impact of the spatial correlation. Since distributed beamforming itself cannot guarantee quality of service (QoS) requirements for given target SINRs with limited cooperation, based on derived closed-form expressions for bounds on SINRs, joint power control is considered with two different approaches. One is optimal, but central processing is required. The other approach is suboptimal, while it can be implemented as a distributed power control algorithm.