This paper considers the optimization of the user and base-station (BS)
association in a wireless downlink heterogeneous cellular network under the
proportional fairness criterion. We first consider the case where each BS has a
single antenna and transmits at fixed power, and propose a distributed price
update strategy for a pricing-based user association scheme, in which the users
are assigned to the BS based on the value of a utility function minus a price.
The proposed price update algorithm is based on a coordinate descent method for
solving the dual of the network utility maximization problem, and it has a
rigorous performance guarantee. The main advantage of the proposed algorithm as
compared to the existing subgradient method for price update is that the
proposed algorithm is independent of parameter choices and can be implemented
asynchronously. Further, this paper considers the joint user association and BS
power control problem, and proposes an iterative dual coordinate descent and
the power optimization algorithm that significantly outperforms existing
approaches. Finally, this paper considers the joint user association and BS
beamforming problem for the case where the BSs are equipped with multiple
antennas and spatially multiplex multiple users. We incorporate dual coordinate
descent with the weighted minimum mean-squared error (WMMSE) algorithm, and
show that it achieves nearly the same performance as a computationally more
complex benchmark algorithm (which applies the WMMSE algorithm on the entire
network for BS association), while avoiding excessive BS handover.

本文研究了基于比例公平性的用户与基站关联的优化问题，提出了分布式的价格更新策略和联合用户关联和功率控制、波束成形优化方法，并证明了该算法优于现有的方法。