Joint network topology optimization and multicell beamforming using mixed integer programming

Coordinated multi-point processing (CoMP) is a promising technique to manage intercell interference and to enhance system performance in cellular networks with single frequency reuse. However, the operational costs of CoMP, such as the associated control signaling and communication overhead and the increase of network complexity, could prevent the practical implementation of CoMP. To ensure that CoMP provides performance improvement to cellular networks at reasonable costs, we consider in this paper the problem of joint multicell basestation assignment and beamformer design (JBAB). We study this problem through a mixed integer second order cone programming (MI-SOCP) approach. We propose a novel MI-SOCP formulation of the JBAB problem and an improved MI-SOCP reformulation with desirable features. Based on the new formulations, we develop a computationally efficient heuristic algorithm that generates close-to-optimal feasible solutions of the JBAB problem. Interestingly, we demonstrate via simulations that our improved MI-SOCP formulation results in dramatically reduced run-time performance of the MI-SOCP solvers. The numerical results also show that the fast heuristic algorithm outperforms the existing methods in terms of both total transmitted power and percentage of feasible solutions obtained while guaranteeing a prescribed signal-to-interference-plus-noise-ratio (SINR) level at each mobile station (MS). In addition, the proposed algorithm yields network topologies that require almost the same transmitted power as that found by the branch-and-bound procedure implemented in IBM ILOG CPLEX in ensuring a predefined SINR target at each MS.