Flow-Level Capacity and Performance in HetNets

The deployment of pico cells to cover traffic hot spots within the footprint of a macro cell provides a powerful approach to meet the massive growth in traffic demands fueled by smartphones and bandwidth-hungry applications. Joint optimization of resource allocation and user association is critical to achieve the maximum capacity benefits and performance gains in such heterogeneous network deployments (HetNets). In order to gain insight in the achievable capacity gains, we examine in the present paper the stability and performance of a HetNet system in the presence of flow-level dynamics. The stability condition reveals that in stationary traffic conditions the maximum capacity can be achieved with a static resource split and traffic association rule, provided that these are suitably selected. This suggests that dynamic adaptation on time scales commensurate with the variations in traffic parameters suffices to extract most of the achievable capacity gains. For the case of static cell boundaries and Proportional Fair scheduling, we also present a method for evaluating the flow-level performance in terms of the distribution of the number of active file transfers and expected transfer delay.