The siting of a GPS reference station on an airport is achieved by minimizing the influence of the environment on the pseudorange measurements, while complying with the operational installation constraints. The CNS Research Laboratory (URE-CNS) of the ENAC has started a study that aims at providing siting guidelines for the French Civil Aviation Authority. The first step of this study consists in implementing a GPS end-to-end simulator that will be used to establish the basic rules for the choice of the best location of the station on an airport with regards to multipath effects. Therefore, the initial goal of the simulator is to analyze the measurement errors induced by simple obstacles (ground, buildings, aircraft ...). The aim of this paper is to present the simulation software which is being developed and the initial results that were obtained.