Interference Modelling for Soft Frequency Reuse in Irregular Heterogeneous Cellular Networks

Soft frequency reuse (SFR) has been proposed as a technique to address the problem of intercell interference (ICI) in cellular networks. A major challenge facing SFR implementation is the efficient allocation of scarce base station (BS) resources like bandwidth and power. This challenge further motivates the need for accurate network modelling, a requirement for optimal SFR algorithms. Particularly, the modelling and optimization of SFR in complex Heterogeneous cellular networks (HetNets) is a current problem in academia and the industry. In this paper, we present a new interference model for HetNets which considers the probabilistic nature of ICI in SFR. The interference probabilities from different BS tiers to the various user (UE) classes are computed. In combination with the analysis of macro BS transmit powers and distance relationships, new equations are also derived for UE signal-to-interference-ratio (SINR) and capacity. A detailed performance analysis is then presented for cases of both Hexagonal and Irregular macro BS placements. Our results show how macro and pico UE perform with respect to the BS power ratios, edge frequencies and placement of BS. This provides useful insights into the development of optimal SFR techniques for HetNets.