Decentralized multi-cell beamforming coordination for multiuser MISO systems

In this paper, we consider a coordinated downlink beamforming problem for a multi-cell network where each multiantenna base station (BS) serves multiple single antenna users. The optimization objective is to minimize the total transmitted power across coordinated BSs while guaranteeing user specific SINR targets. We propose a decentralized beamformer design algorithm which is based on primal decomposition method and uplink-downlink duality. Original optimization problem is decomposed via primal decomposition into two levels, i.e., BS specific subproblems managed by a network-level master problem. Master problem is solved at each BS using a subgradient method, and it requires a limited amount of backhaul information exchange between BSs. The main contribution of the paper is an uplink-downlink duality based beamformer design for solving each BS specific subproblem. Due to properties of uplink-downlink duality, convex optimization tools are not required in the proposed approach. Since the original problem is convex, global convergence of the algorithm is guaranteed and optimal beamformers are achieved across BSs. Moreover, feasible beamformers, which satisfy the SINR targets, are guaranteed at each iteration during the convergence process. Convergence behavior of the proposed approach is studied through simulations.