Coordinated scheduling and beamforming for multicell spectrum sharing networks using branch & bound

We consider the downlink of a multicell network where neighboring multi-antenna base stations share the spectrum and coordinate their frequency and spatial resource allocation strategies to improve the overall network performance. The objective of the coordination is to maximize the number of users that can be scheduled, meeting their quality-of-service requirements with the minimum total transmit power. The coordinated scheduling and multiuser transmit beamforming problem is combinatorial; we formulate it as a mixed-integer second-order cone program and propose a branch & bound algorithm that yields the optimal solution with relatively low-complexity. The algorithm can be used to motivate or benchmark approximation methods and to numerically evaluate the gains due to spectrum sharing and coordination.