  This paper develops a new approach to the modeling and analysis of HetNets
that accurately incorporates coupling across the locations of users and base
stations, which exists due to the deployment of small cell base stations (SBSs)
at the places of high user density (termed user hotspots in this paper).
Modeling the locations of the geographical centers of user hotspots as a
homogeneous Poisson Point Process (PPP), we assume that the users and SBSs are
clustered around each user hotspot center independently with two different
distributions. The macrocell base station (BS) locations are modeled by an
independent PPP. This model is consistent with the user and SBS configurations
considered by 3GPP. Using this model, we study the performance of a typical
user in terms of coverage probability and throughput for two association
policies: i) Policy 1, under which a typical user is served by the open-access
BS that provides maximum averaged received power, and ii) Policy 2, under which
the typical user is served by the small cell tier if the maximum averaged
received power from the open-access SBSs is greater than a certain power
threshold; and macro tier otherwise. A key intermediate step in our analysis is
the derivation of distance distributions from a typical user to the open-access
and closed-access interfering SBSs. Our analysis demonstrates that as the
number of SBSs reusing the same resource block increases, coverage probability
decreases whereas throughput increases. Therefore, contrary to the usual
assumption of orthogonal channelization, it is reasonable to assign the same
resource block to multiple SBSs in a given cluster as long as the coverage
probability remains acceptable. This approach to HetNet modeling and analysis
significantly generalizes the state-of-the-art approaches that are based on
modeling the locations of BSs and users by independent PPPs.
