  Owing to its flexibility in modeling real-world spatial configurations of
users and base stations (BSs), the Poisson cluster process (PCP) has recently
emerged as an appealing way to model and analyze heterogeneous cellular
networks (HetNets). Despite its undisputed relevance to HetNets -- corroborated
by the models used in industry -- the PCP's use in performance analysis has
been limited. This is primarily because of the lack of analytical tools to
characterize performance metrics such as the coverage probability of a user
connected to the strongest BS. In this paper, we develop an analytical
framework for the evaluation of the coverage probability, or equivalently the
complementary cumulative density function (CCDF) of
signal-to-interference-and-noise-ratio (SINR), of a typical user in a K-tier
HetNet under a max power-based association strategy, where the BS locations of
each tier follow either a Poisson point process (PPP) or a PCP. The key
enabling step involves conditioning on the parent PPPs of all the PCPs which
allows us to express the coverage probability as a product of sum-product and
probability generating functionals (PGFLs) of the parent PPPs. In addition to
several useful insights, our analysis provides a rigorous way to study the
impact of the cluster size on the SINR distribution, which was not possible
using existing PPP-based models.
