  Commonly considered user association frameworks in millimeter-wave
communications are based on the sum rate maximization, and they essentially
neglect user specific rate and service requirements. Furthermore, new features
of millimeter-wave communications including spatial multiplexing, connectivity
to multiple coordinated base stations and dense base station deployment are not
considered. In this work, we propose a two-step optimization framework for
single-shot user association in dense millimeter-wave networks which takes into
account users' rate requirements, multi-connectivity, and hybrid transceiver
architecture for spatial multiplexing. The proposed framework considers
multiple RF chains at each base station and assigns them to different users
that also have multiple RF chains for connectivity with more than one base
station. In the first step, the objective of the user association is to
maximize the number of users with satisfied rate requirements while minimizing
network underutilization. In the second step, remaining RF chains are assigned
to users, whose rate requirement has not been met, such that network sum rate
is maximized. This is a novel problem formulation for user associate in
millimeter-wave networks. We propose low complexity sub-optimal user
association algorithms based on this formulation, numerically evaluate the
optimal and sub-optimal solutions, and compare them to the conventional
association approaches in terms of the number of associated users and network
sum rate.
