Decentralized base station assignment in combination with downlink beamforming

Decentralized base station (BS) assignment methods with limited backhaul information exchange are proposed to be combined with decentralized optimal multi-cell minimum power beamforming and Zero-Forcing (ZF) beamforming techniques. The aim of the combined BS assignment and downlink beamforming is to minimize sum power while guaranteeing a minimum SINR per user. A major finding is that a simple ZF beamforming with the optimal decentralized BS assignment, and with limited backhaul information exchange obtains near optimal performance near the cell edge when the user-specific SINR targets are high. Thus, only marginal gains are available from more complex BS assignment and beamforming approaches. However, in the case of low user-specific SINR targets, there is a significant gain available at the cell edge from the optimal beamforming and BS assignment. For example, a simple maximum channel norm selection based BS assignment method with the optimal minimum power beamforming can obtain much of this gain.