Cell Association With Load Balancing in Nonuniform Heterogeneous Cellular Networks: Coverage Probability and Rate Analysis

To meet the ever-growing traffic demand and address the cell capacity shortage problem, associating end users to various tiers of cells in a multitier cellular network appears to be a promising approach. In this paper, we consider a nonuniform heterogeneous cellular network (NuHCN) and propose a cell association scheme that selectively mutes certain small-cell base stations (BSs) and covers end users by cell range extension (via cell biasing) for achieving load balancing. The envisaged NuHCN is comprised of two tiers of BSs, i.e., macro- and small-cell BSs, deployed according to three independent homogeneous Poisson point processes for BSs and end users, respectively. Accordingly, the available space is divided into two subspaces. In the inner subspace, the end users are associated only with a macrocell BS based on the unbiased maximum received power scheme since the small-cell BSs therein are deactivated. In the outer subspace, where the macrocell BS coverage is comparatively poor, the end users are associated with either a macrocell BS or a microcell BS based on the biased/unbiased maximum received power scheme. Cell range extension-based cell association allows the macrocell users in the outer subspace to efficiently utilize the resources of the lightly loaded small-cell BSs, resulting in improved network coverage and capacity. Based on the proposed cell association scheme, we analyze the signal-to-interference plus noise ratio (SINR) distribution and deduce expressions for coverage probability and rate coverage. Numerical results show that, contrary to the uniform case, biasing has distinct effects on the coverage and rate performance of an NuHCN.