  In a millimeter wave (mmWave) network, user association, the process of
deciding as to which base station (BS) a given user should associate with, is a
crucial process which affects the throughput and delay performance seen by
users in the network and the amount of load at each BS. In the existing
research literature, the stability region of a user association policy, i.e.,
the set of user arrival rates for which the user association policy stabilizes
the network, has not been analytically characterized for any user association
policy for mmWave networks. In this paper, we study the user association
problem in mmWave networks and compare the performance of four user association
policies: Signal to Noise Ratio (SNR) based, Throughput based, Load based and
Mixed. All these policies are simple, easy to implement, distributed and
online. We use a Continuous Time Markov Chain (CTMC) model and Lyapunov
function techniques to analytically characterize the stability region of each
of the above four user association policies. We also evaluate the performance
of the above four user association policies in a large mmWave network, in which
link qualities fluctuate with time and users are mobile, via detailed
simulations. Our results show that the Throughput based policy outperforms the
other three user association policies in terms of stability region as well as
average throughput, average delay and fairness performance.
