Optimal Dynamic Point Selection for Power Minimization in Multiuser Downlink CoMP

TL;DR

This paper proposes an optimal solution framework for dynamic base-station selection and beamforming in multiuser CoMP systems to minimize power consumption, effectively handling binary association variables through relaxation techniques.

Contribution

It introduces a novel relaxation-based approach to jointly optimize BS association and beamforming, achieving optimal or near-optimal solutions for power minimization in CoMP systems.

Findings

Relaxed problems can be solved optimally using quadratic programming.

The first design objective yields an optimal solution for the original problem.

Simulation shows significant power savings over fixed association schemes.

Abstract

This paper examines a CoMP system where multiple base-stations (BS) employ coordinated beamforming to serve multiple mobile-stations (MS). Under the dynamic point selection mode, each MS can be assigned to only one BS at any time. This work then presents a solution framework to optimize the BS associations and coordinated beamformers for all MSs. With target signal-to-interference-plus-noise ratios at the MSs, the design objective is to minimize either the weighted sum transmit power or the per-BS transmit power margin. Since the original optimization problems contain binary variables indicating the BS associations, finding their optimal solutions is a challenging task. To circumvent this difficulty, we first relax the original problems into new optimization problems by expanding their constraint sets. Based on the nonconvex quadratic constrained quadratic programming framework, we show that these relaxed problems can be solved optimally. Interestingly, with the first design objective, the obtained solution from the relaxed problem is also optimal to the original problem. With the second design objective, a suboptimal solution to the original problem is then proposed, based on the obtained solution from the relaxed problem. Simulation results show that the resulting jointly optimal BS association and beamforming design significantly outperforms fixed BS association schemes.