Ambiguity Recovery for GPS Long Range Kinematic Positioning

Shaowei Han

Abstract:	Precise long range GPS kinematic positioning to centimetre accuracy requires the carrier phase ambiguities to be resolved. There are many techniques for on-the-fly ambiguity resolution for short baselines (<2Okm), but none for long range applications (tens to thousands of kilometres). The traditional technique of fixing the integer ambiguity is by initialisation involving a period of static positioning at the beginning of a kinematic session. The weakness of this technique is that it requires a re-initialisation procedure if cycle slips occur during the period the antenna is in motion. Recently, ambiguity resolution procedures have been developed that operate even when the antenna is moving, the so-called “on-the-fly” ambiguity resolution techniques. Ambiguity resolution on-the-fly for long range kinematic mode of positioning, however, is a very difIicult task. In this paper, a technique of ambiguity recovery is suggested to recover integer ambiguities when cycle slips occur or if the data gap is shorter than a few minutes. This technique comprises three steps. The first step uses the widelane carrier phase observation, together with the combined observation (-7~, + 9q,) and the precise pseudoranges, to detect and remove cycle slips in the one-way carrier phase data. Normally, the cycle slips, when there are no serious multipath problems, can be detected and removed in this step. The second step uses two combined carrier phase observables ( q+ - ‘pz and -39, + 4q, ) and the predicted roving receiver position, to detect and remove cycle slips using a Kalman filter algorithm applied to the Ambiguity Function implementation. For the applications when position can be predicted with relatively high precision over a short period, such as the tracking of a railway vehicle, large ship, or aircraft, the second step will be very powerful. The last step involves a validation procedure which determines which integer cycle ambiguity set will be significantly better than other candidate sets. The suggested technique has been successfully tested for various baseline lengths. Results of an aircraft positioning experiment (140km) and a railway tracking experiment (295km) will be presented.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	349 - 360
Cite this article:	Han, Shaowei, "Ambiguity Recovery for GPS Long Range Kinematic Positioning," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 349-360.
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