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Distributed SINR Balancing Beamformer Design for Coordinated Muti-Cell Systems

This paper considers the beamformer design problem of coordinated multi-antenna base stations (BSs), where the BSs jointly optimize their respective beamformers to improve the overall system performance. Previous research aimed at minimizing the sum transmitted power of all BSs under per-user signal to interference plus noise ratio (SINR) constraints. However, feasibility of the SINR constraints cannot be determined in advance. In this paper, we focus on the design criteria of maximal achievable worst-case user's SINR for a particular quality of service (QoS) requirement under multiple sets of power constraints. The main contribution of the paper is an efficient algorithm for finding the globally optimal beamformers across all BSs. The proposed algorithm is based on a generalization of the uplink-downlink duality to the multi-cell setting along with an application of subgradient methods. An important feature is that it leads to a distributed implementation in the coordinated multi-cell system.