This paper proposes energy-efficient coordinated beamforming strategies for multi-cell multi-user multiple-input single-output system. We consider a practical power consumption model, where part of the consumed power depends on the base station or user specific data rates due to coding, decoding and backhaul. This is different from the existing approaches where the base station power consumption has been assumed to be a convex or linear function. Two optimization criteria are considered, namely network energy efficiency maximization and weighted sum energy efficiency maximization. We develop successive convex approximation based algorithms to tackle these difficult nonconvex problems. We further propose decentralized implementations for the considered problems, in which base stations perform parallel and distributed computation based on local channel state information and limited backhaul information exchange. The decentralized approaches admit closed-form solutions and can be implemented without invoking a generic external convex solver. The effect of pilot contamination caused by pilot reuse is also taken into account in the energy efficiency problems. To achieve energy efficiency improvements with a limited number of pilot resources, we propose a heuristic energy-efficient pilot allocation strategy to mitigate the pilot contamination effect. The numerical results are provided to demonstrate that the rate dependent power consumption has a large impact on the system energy efficiency, and, thus, has to be taken into account when devising energy-efficient transmission strategies. We also investigate the effect of pilot contamination and show that the proposed pilot allocation strategy achieve significant performance improvements when a limited number of pilot resources is available.
['Oskari Tervo', 'Antti Tölli', 'Markku J. Juntti', 'Le-Nam Tran']
Energy-Efficient Beam Coordination Strategies with Rate Dependent Processing Power