GPS/GALILEO/GLONASS Hybrid Satellite Constellation Simulator Ð GPS Constellation Validation and Analysis

The advent of the European Galileo navigation system, the modernization of the American GPS and the update of the Russian GLONASS satellite constellation will lead to an improved Global Navigation Satellite System (GNSS). Availability, reliability and accuracy are key parameters in evaluating GNSS performance. In order to completely understand the benefits that will bring Galileo, and the update of GLONASS, it is necessary to evaluate the performance improvement using a hybrid ION 61st Annual Meeting/ The MITRE Corporation & Draper Laboratory, 27-29 June 2005, Cambridge, MA 733 GPS/Galileo/GLONASS Satellite Constellation simulator, the so-called project titled Software Defined Simulator (SDS). The development of an accurate hybrid constellation simulator is a key point in any GNSS Signal Generator simulator. The use of a Radio Frequency (RF) or Intermediate Frequency (IF) signal generator simulator for performance testing of GNSS receivers is obvious, allowing a repeatable and a completely controlled test environment which ensures the efficiency of the development of any GNSS receiver. The use of such a simulator allows also characterizing the receiver’s behavior in unusual or unexpected conditions. The SDS project results showing the capabilities of the hybrid GNSS constellation are presented, such as worldwide simulated availability and accuracy for various GPS, Galileo and GLONASS possible combinations. Spatial and temporal performances are presented and compared. The following parameters are considered in order to evaluate the performance of the hybrid GNSS navigation system compared to different satellite constellations combinations: visibility and various Dilution Of Precision (DOP) parameters. In this paper, the validation of the GPS satellite constellation is emphasized, the generation of the GPS constellation being done using either almanacs or broadcast ephemeris. In order to do so, comparisons with results obtained either from other existing satellite constellation simulators, from real GPS receivers or from precise ephemeris are done. Different parameters defining the satellite constellation configurations are considered for the validation, such as coordinates of the satellites, elevation, azimuth and visibility.