  The growing complexity of heterogeneous cellular networks (HetNets) has
necessitated a variety of user and base station (BS) configurations to be
considered for realistic performance evaluation and system design. This is
directly reflected in the HetNet simulation models proposed by standardization
bodies, such as the third generation partnership project (3GPP). Complementary
to these simulation models, stochastic geometry-based approach, modeling the
locations of the users and the K tiers of BSs as independent and homogeneous
Poisson point processes (PPPs), has gained prominence in the past few years.
Despite its success in revealing useful insights, this PPP-based K-tier HetNet
model is not rich enough to capture spatial coupling between user and BS
locations that exists in real-world HetNet deployments and is included in 3GPP
simulation models. In this paper, we demonstrate that modeling a fraction of
users and arbitrary number of BS tiers alternatively with a Poisson cluster
process (PCP) captures the aforementioned coupling, thus bridging the gap
between the 3GPP simulation models and the PPP-based analytic model for
HetNets. We further show that the downlink coverage probability of a typical
user under maximum signal-to-interference-ratio association can be expressed in
terms of the sum-product functionals over PPP, PCP, and its associated
offspring point process, which are all characterized as a part of our analysis.
We also show that the proposed model converges to the PPP-based HetNet model as
the cluster size of the PCPs tends to infinity. Finally, we specialize our
analysis based on general PCPs for Thomas and Matern cluster processes. Special
instances of the proposed model closely resemble the different configurations
for BS and user locations considered in 3GPP simulations.
