Distributed Coordinated Multi-Cell Transmission Based on Dual Decomposition

A distributed solution is proposed for the coordinated multi-cell multi-antenna minimum power beamformer design problem with single-antenna users. 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 coupled interference terms are handled by taking local copies of the terms at each BS and enforcing consistency between them. The consistency constraints are then decoupled by a standard dual decomposition approach leading to a distributed algorithm. The proposed method is able to guarantee feasible solutions even if the interference information is outdated or incomplete, at the possible cost of increased sum power. In addition, the proposed approach allows for a number of special cases, where the backhaul information exchange is reduced at the cost of somewhat sub-optimal performance. The performance of the proposed coordinated multi-cell transmission is compared with the coherent multi-cell beamforming, as well as, with inter-cell interference nulling in different scenarios with varying interference. The numerical examples demonstrate that a near-optimal performance can be achieved even with significantly reduced backhaul information exchange.