The siting of a GPS reference station on an airport is achieved by minimizing the influence of the environ-ment on the pseudorange measurements, while comply-ing with the operational installation constraints. The CNS Research Laboratory (URE-CNS) of theENAC 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 measure-ment errors induced by simple obstacles (ground, build-ings, aircraft ...). The aim of this paper is to present the simulation software which is being developed and the initial results that were obtained. The simulator is comprised of three cascaded modules. The first mod-ule computes the satellite positions at every input epoch, The second module simulates the propagation channel. It is derived from the MUSICA tool (MUltipath SImu-lat ion for Civil Aviation) that was previously developed by the ENAC for classical navaids multipath simulation. It generates the disturbed GPS signal delivered by the anl.enna of the station to its receiver front-end. Then, this signal is handed to the last module, that simulates a generic GPS receiver and delivers the range measure-ment errors induced by the perturbations introduced in the propagation channel. The initial results show the ef-fect of simple reflecting objects, such as the ground and metallic surfaces.