An Analytical Model for Flow-Level Performance in Heterogeneous Wireless Networks

Modern cellular networks are becoming denser, less regularly planned, and increasingly heterogeneous, making performance analysis challenging. We develop a flexible and accurate model of such heterogeneous networks (HetNets) consisting of K tiers of randomly located base stations (BSs), with different densities, transmit powers, and radio access technologies (RATs). Our main goal is to understand the impact of flow level dynamics on such a system, assuming non-saturated users that randomly generate download requests ("flows"). We do so by deriving analytically the per flow delay, the load, the utilization and the congestion probability of BSs in different tiers. We base our analysis on stochastic geometry, to understand the impact of topological randomness and intra-and inter-tier interaction, and queueing theory, to model the competition between concurrent flows within the same BS, for each RAT. This allows us to model the interference more realistically as a function of network load. We apply our model to the case of a 2-tier network based on LTE and Wi-Fi and study different user inter-tier association criteria, such as off-load, max-SINR association, and min-delay association. Our results provide some interesting qualitative and quantitative insights about the impact of these association policies and different traffic intensities.