GPS and Galileo performance evaluations for multiple reference station network positioning.

摘要

The European Galileo and the modernization of the current Global Positioning System (GPS) will substantially increase the available signals to Global Navigation Satellite Systems (GNSS) users. Past simulation studies have shown that Galileo performs better than the current GPS under high ionosphere conditions and for medium length reference-rover separations when using the Single Reference Station (SRS) approach. When the baseline increases beyond 30 km, ambiguity resolution performance deteriorates, and carrier phase fixed integer ambiguity kinematic positioning becomes difficult to achieve for either system. The Multiple Reference Station (MRS) approach reduces the effect of correlated errors more effectively than the traditional SRS approach and hence provides better positioning accuracies over increased baseline distances. The Multiple Reference Station Tightly Coupled (MRS-TC) approach is an efficient MRS technique developed at the University of Calgary. This study extends past research through an evaluation of Galileo compared to GPS for the MRS approach. The focus is on an independent assessments of the MRS-TC approach dual frequency Galileo and a GPS using 24/27 GPS/Galileo and 29/30 GPS/Galileo constellations, in terms of positioning accuracy and ambiguity resolution reliability. Several networks of varying sizes are analysed under different ionospheric conditions using a measurement simulation software system.; The analysis shows that for all the simulated baselines and error levels, the MRS-TC approach applied to Galileo always offers the best results compared to SRS GPS and Galileo and the MRS-TC GPS cases. The study concludes that, for low ionospheric error conditions, the MRS-TC for Galileo delivers reliable cm-level positioning errors for extended baselines up to 120 km, whereas for medium and high ionospheric conditions, it provides reliable cm-level positioning errors for baselines up to 90 and 30 km, respectively. For high ionospheric conditions and extended baselines beyond 30 km, none of the systems provide reliable results under the simulation conditions and algorithms used. These results obtained here are based on 24/27 GPS/Galileo and 29/30 GPS/Galileo constellations however they will vary depending upon the constellation, i.e. the number of satellites deployed for each system in the future since the ambiguity resolution performance is in part a function of the number available satellites.