Stability Analysis of Simple and Online User Association Policies for Millimeter Wave Networks

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 performances 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; our analysis provides several insights into the performances of the policies. We also evaluate the performances 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, fairness and energy efficiency performance.