Modeling and Analysis of Two-Tier HetNets With Cognitive Small Cells

Heterogeneous networks (HetNets), which consist of traditional macro-cells overlaid with newly envisioned small cells (e.g., femtocells, picocells, microcells, and nanocells), are conceived as an appealing technology to satisfy the ever-increasing capacity requirements in future mobile networks. The cross-tier interference management is a challenging problem in conventional HetNets due to the large-scale deployment of small cells in random locations, and the lack of complete coordination. However, cognitive HetNets, where small-cell base stations are with cognitive capabilities (e.g., achieved through spectrum sensing), can efficiently overcome the posed challenge. In this paper, considering a two-tier cognitive HetNet, we utilize the statistic tool of stochastic geometry to model and analyze the coverage performance for macro-cell and small-cells over general Nakagami-m fading channels. Specifically, the exact closed form expressions of outage probability for per-tier cell-edge users with and without cognitive interference coordination are derived, respectively. More attractively, the theoretically analytical results can be used to help to design the constraints on the configurations of small cells considering the minimum requirements of coverage performance for macro-cell and small-cell. Simulation results validate our analysis.