HetNet Capacity Optimization under Optimal Femtocell Operation in LTE-U

Heterogeneous Network (HetNet) has been a major feature for next generation wireless networks, where femtocell has attracted much attention as a most promising radio access technology (RAT) for providing improvements on network capacity, service coverage and power efficiency. And for the efficient utilization of scarce spectral resource, coexistence/sharing of unlicensed band between wireless fidelity (Wi-Fi) and Long Term Evolution (LTE) systems has recently been proposed and investigated. It is shown that analysis by Voronoi diagram achieves superior performance under homogeneous environment. In this paper, we extend the Voronoi diagram approach to HetNet environment with Wi-Fi and LTE femtocells, which is shown to achieve superior performance under homogeneous network. For the HetNet, we formulate an optimization problem, which is derived from a weighted Voronoi tessellation and the corresponding characteristic functions, to maximize network capacity over an optimal femtocell operation scheme in LTE-U. For the optimal femtocell operation, we provide an optimal AP density ratio under the objective of HetNet capacity maximization with convex analysis, where partial femto APs are turned to open access mode in the HetNet coverage. Simulation results are provided to demonstrate effectiveness of the proposed algorithm, and validate importance of the AP density ratio and the transmit power ratio to network capacity. This analysis can be easily extended to HetNets with multiple RATs.