Study of the User Equivalent Range Error for Global Navigation Satellite Systems

Satellite navigation systems such as GPS, GLONASS or the future European system GALILEO are made of satellites constellations, which send out signals which allow any user carrying an appropriate receiver to calculate the distance between him and the satellite. This distance is called pseudorange. The user position can be determined from these pseudoranges thanks to a triangulation algorithm that requires four visible satellites. Of course, the precision of the so calculated positions depends on the quality of pseudorange measurements, which can be disrupted by many error sources that can be represented as a global error factor called UERE. The aim of the work presented in this document is to measure this factor which characterizes GNSS range errors, and to develop tools to do it. Since UERE is a function of several parameters which caracterize the receiver, the user’s environnement, the weather, etc., its study will lead us to a better comprehension of the origin and behaviours of GNSS errors. This knowledge is necessary to improve the systems of navigation ; indeed, the errors must be corrected in order of importance. Moreover, the next step is to use these results coming from measurements to modelize UERE ; that would allow us to have a complete knowledge of it and also to make it more operational, in order to determine if GPS measurements of position are reliable or not. It is essential for applications that require a high level of certification, for instance aeronautical applications (GPS guided aircraft, etc.)