Coverage performance of heterogeneous cellular networks with dependent cell deployment

To offload congested base stations (BSs) in the cellular network, deploying low-power BSs overlaid with existing high-power BSs that forms the heterogeneous cellular network (HCN) with multiple tiers, has been widely considered in the literature. For analytical tractability, the locations of BSs are often modeled as the independent Poisson point process (PPP). However, the independence assumption may lead to arbitrarily small distances between low-power and high-power BSs. In practice, low-power BSs should not be placed too close to the high-power BSs because otherwise their mutual interference will diminish the gain provided by offloading. Besides, previous work often ignores the actual load of each BS but assuming that all BSs are fully loaded. For the emerging HCN, an analytical model that characterizes the dependent cell deployment with the use of cell range extension (CRE) technique is proposed in this paper. The proposed model avoids the BSs of different tiers being arbitrarily close in distance and takes into account the BS load as a function of resource utilization. Based on the proposed modeling approach, we derive the coverage probabilities and the average user rates of different tiers. Numerical results are presented to verify the analysis accuracy and demonstrate the interplay between key system parameters and the resultant performance.