Monotonic optimization framework for coordinated beamforming in multicell networks

Intercell interference is the major limiting factor in wireless multicell networks. Recently, it has been shown that significant performance gains can be achieved by cooperation among base stations. Different degrees of cooperation are possible. In this paper, cooperation in the form of intercell interference management is considered. The base stations are equipped with multiple antennas, while the mobile terminals only have a single antenna. The base stations jointly coordinate beamforming and scheduling, and thus perform a weaker form of cooperation among base stations than suggested in recently proposed joint transmission techniques. The terminals treat intercell interference as noise. The corresponding resource allocation problem is cast as a utility maximization problem, which includes common performance objectives such as the arithmetic mean, the geometric mean, and the max-min operation of achievable user rates. The resulting utility maximization problem is a nonconvex optimization problem. After a suitable reformulation, the problem can be solved to global optimality using the framework of monotonic optimization. Although, the numerical complexity of the proposed method is exponential, the reformulation step leads to an optimization problem which only scales in the number of mobile terminals instead of the entire set of physical layer parameters. In essence, the proposed framework represents a powerful tool for computing benchmarks for certain scenarios and utility functions under jointly optimal beamforming and scheduling.