  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.
