Ionosphere Weighted GPS Cycle Ambiguity Resolution

George Chia Liu and Gérard Lachapelle

Abstract:	Integer Ambiguity constraint is essential in precise GPS positioning applications. The performance and reliability of the ambiguity resolution process are being hampered by the culmination of the eleven-year solar cycle. The traditional approach to mitigate the high ionospheric effect has been either to reduce the inter-station separation or to form ionosphere-free observables. Neither is satisfactory: the first restricts the operating range, and the second no longer possesses the "integerness" of the ambiguities. A third generalised approach is introduced herein, whereby the zero ionosphere weight constraint, or pseudo-observable, with an appropriate weight is added to the Kalman Filter algorithm. The weight can be tightly fixed yielding the model equivalence of an independent L1/L2 dual-band model. At the other extreme, an infinite floated weight gives the equivalence of an ionosphere-free model, yet preserves the ambiguity integerness. A stochastically tuned, or weighted, model provides a compromise between the two extremes. Two days of selected Swedish GPS Network data sets from ionospherically active (up to 15 ppm) and moderate (up to 4 ppm) days, forming baselines up to 400 km, have been analysed. The ionosphere weight model yielded a 90% range of correct widelane ambiguities within three minutes, regardless of inter-station distance.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	889 - 899
Cite this article:	Liu, George Chia, Lachapelle, Gérard, "Ionosphere Weighted GPS Cycle Ambiguity Resolution," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 889-899.
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