Investigation of Combined GPS/GALILEO Cascading Ambiguity Resolution Schemes

W. Zhang, M.E. Cannon, O. Julien, P. Alves

Abstract:	Global Navigation Satellite Systems (GNSS) are evolving to a new era due to the modernization of the current GPS and the upcoming GALILEO systems. Three civil frequencies will be available for both systems, two of which are overlaid. This enables the possibility of instantaneous carrier phase ambiguity resolution. Some methods such as the Three-Carrier Ambiguity Resolution (TCAR) and Cascading Integer Resolution (CIR) have been proposed for modernized GPS and GALILEO, respectively, however they are generally only applicable to very short baselines. In this paper, some combined cascading ambiguity resolution schemes are presented and are aimed at faster and more reliable ambiguity resolution over longer baselines. One of these methods will be used to evaluate the performance of three frequency systems. In these schemes, the concept of cascading ambiguity resolution is adopted using the geometry-based model instead of the geometry-free model (used in TCAR/CIR) to estimate the user position as well as the ambiguities. To get the most reliable solutions, the LAMBDA ambiguity search method is performed instead of integer rounding as proposed for TCAR/CIR. GALILEO and modernized GPS are integrated in a loosely coupled mode and another integration mode which takes into account the overlaid frequencies is also introduced for comparison. The schemes are realized by processing simulated data tests using three filters for three cascading steps. A cascading method based on one filter is also presented and analyzed for comparison. Static tests with 1 to 50 km baselines are analyzed at normal error levels using the geometry-based cascading ambiguity resolution scheme for the two systems individually and combined. The results show that very fast ambiguity resolution can be obtained using the scheme, and even instantaneous ambiguity resolution is possible over 1 to 10 km baselines using the combined system.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2599 - 2610
Cite this article:	Zhang, W., Cannon, M.E., Julien, O., Alves, P., "Investigation of Combined GPS/GALILEO Cascading Ambiguity Resolution Schemes," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2599-2610.
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