Femtocells, or home base stations, are a potential future solution for operators to
increase indoor coverage and reduce network cost. In a real WiMAX femtocell deployment
in residential areas covered by WiMAX macrocells, interference is very likely to occur
both in the streets and certain indoor regions. Propagation models that take into
account both the outdoor and indoor channel characteristics are thus necessary for
the purpose of WiMAX network planning in the presence of femtocells. In this paper,
the finite-difference time-domain (FDTD) method is adapted for the computation of
radiowave propagation predictions at WiMAX frequencies. This model is particularly
suitable for the study of hybrid indoor/outdoor scenarios and thus well adapted for
the case of WiMAX femtocells in residential environments. Two optimization methods
are proposed for the reduction of the FDTD simulation time: the reduction of the simulation
frequency for problem simplification and a parallel graphics processing units (GPUs)
implementation. The calibration of the model is then thoroughly described. First,
the calibration of the absorbing boundary condition, necessary for proper coverage
predictions, is presented. Then a calibration of the material parameters that minimizes
the error function between simulation and real measurements is proposed. Finally,
some mobile WiMAX system-level simulations that make use of the presented propagation
model are presented to illustrate the applicability of the model for the study of
femto- to macrointerference.
