Distributed implementation of coordinated multi-cell beamforming

A distributed implementation of coordinated multi-cell beamforming with single-antenna users in a time-correlated fading scenario is considered. The minimum power beamformers are obtained locally at each base station (BS) relying on limited backhaul information exchange between adjacent BSs. The original centralised problem is reformulated such that the BSs are coupled by real-valued inter-cell interference terms. The problem is then decoupled by a standard dual decomposition approach leading to a distributed algorithm. The method is able to guarantee feasible solutions even if the interference information is incomplete or outdated. Occasional high peaks in the transmitted power due to outdated interference terms are alleviated by switching to interference nulling mode when necessary. The performance of the proposed coordinated multi-cell transmission is compared with the coherent multi-cell beamforming, as well as, with interference nulling in different time-correlated fading scenarios with varying interference. The numerical examples demonstrate that a near-optimal performance can be achieved even with significantly reduced backhaul information exchange and with relatively high velocities and/or low signalling rates.