The Impact of Future Global Navigation Satellite Systems on Precise Carrier Phase Positioning

Todd Richert and Naser El-Sheimy

Abstract:	With the implementation of GPS modernization and the deployment of the Galileo satellites, satellite navigation users will have access to six carrier phase measurements from each satellite. In order to exploit the potential benefits of these services, developers must understand the impact this increased number of signals will have on positioning algorithms and capabilities. A software simulator has been used in conjunction with a Global Navigation Satellite System (GNSS) processing engine to perform experiments that shed light on future satellite positioning performance. Ambiguity validation has proven to be difficult with the current GPS system, especially for longer baselines, and this will continue to be an important task for high precision applications in the future. This investigation tests the ability to validate potential ambiguity sets for the current and future GNSS signals. It is shown that the inclusion of a third frequency with GPS will not greatly improve the ability to discriminate between correct and incorrect ambiguity sets, but when triple frequency Galileo is combined with triple frequency GPS, ambiguity validation becomes much more reliable for both short and long baselines. For the currently available GPS signals, fixing the ambiguities to correct integer values is imperative to exploit the highest accuracy from the carrier phase measurements. This will also remain true when three GPS frequencies are available. When a combined triple frequency GPS/Galileo system is employed, the impact of fixing ambiguities to incorrect integer values is reduced. In fact, the tests in this investigation show that a solution resulting from incorrectly constrained integers may actually be more accurate than the float solution. Partial fixing with the current and future Global Navigation Satellite Systems is also demonstrated. It is shown that the technique of partial fixing does indeed improve ambiguity validation capabilities and provides position accuracies comparable to a fully fixed solution. This improvement was found in all positioning scenarios with both GPS and Galileo signals. In the case of triple frequency combined GPS and Galileo with large ionospheric errors, the partially fixed solution actually gave more accurate position results than the fully fixed ambiguity solution.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	2124 - 2135
Cite this article:	Richert, Todd, El-Sheimy, Naser, "The Impact of Future Global Navigation Satellite Systems on Precise Carrier Phase Positioning," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 2124-2135.
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