Load-aware heterogeneous cellular networks: Modeling and SIR distribution

Heterogeneous cellular networks (HCNs) are characterized by cells whose coverage areas may vary by orders of magnitude. It is natural therefore that their user populations (and hence traffic loads) will vary similarly. Yet, to date, random spatial models developed for HCNs generally assume that all base stations (BSs) are always transmitting and hence implicitly have the same load. This paper incorporates a flexible notion of BS load by conditionally thinning the interference field, conditional on the connection of a typical mobile to its serving BS. We derive the coverage probability - i.e. the Signal-to-Interference-Ratio (SIR) distribution - for a typical mobile in a K-tier HCN where each tier has an arbitrary load characterized by a traffic factor p_k ∈ [0, 1], where p_k = 1 is fully loaded. Fully-loaded models are observed to be extremely pessimistic in terms of coverage, and the analysis shows that adding lightly loaded access points (e.g. pico or femtocells) to the macrocell network always increases the coverage probability.