GPS and GLONASS Carrier Phase Ambiguity Resolution

David Walsh and Peter Daly

Abstract:	Differential carrier phase GPS positioning is successfully used world-wide to provide static and kinematic positioning accuracy at the centimetre/millimetre level. However, there are a number of real time applications which require a very high level of system performance and these would benefit from a greater satellite availability. One of the most stringent of these applications is Category III precision approach and landing of aircraft using carrier phase. Another demanding application is engineering surveying on sites where there are many obstructions so the satellite availability is low. In order to achieve the required accuracy in real time the ambiguities must be resolved very quickly. Fast centimetre level differential positioning on static baselines using GPS carrier phase ambiguity resolution has been shown to be possible. These methods commonly use search techniques. Until the ambiguities are resolved GPS will not provide centimetre level positioning. The time to resolve the ambiguities can be significantly affected by the number of satellites available. The most obvious way to increase the number of satellites is by combining GPS and GLONASS. In January 1996 GLONASS achieved a full constellation of 24 operating satellites plus one spare satellite in orbit. There are, currently, a total of 46 operating satellites when GLONASS and GPS are combined. The Institute of Satellite Navigation (ISN) has developed a 20 channel GPS/GLONASS receiver capable of obtaining single frequency carrier phase and code phase observables to take full advantage of having two satellite systems. Each channel can track either GPS or GLONASS satellites. The ISN has also recently developed a 12 channel dual frequency GPS/GLONASS receiver for the European Space Agency. Static differential GLONASS carrier phase positioning has already been performed at the ISN using long periods of data [ 1,2]. One of the problems with using GLONASS is that as the GLONASS satellites transmit signals at different frequencies the signals have different delays in the receiver. These- delays have to be accounted for in order to resolve the ambiguities. This paper describes research carried out at the ISN to perform fast ambiguity resolution on static baselines using GPS and GLONASS carrier phase measurements provided by the Leeds GNSS receivers. Algorithms have been developed at the ISN to calculate a static differential carrier phase position solution using a search algorithm with GPS and GLONASS satellites, just GPS, or just GLONASS. The calibration/mitigation of the different GLONASS receiver delays will be outlined. Finally, results of static tests are given whit show that centimetre level accuracy for a GPYGLONASS carrier phase solution can be achieved.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	899 - 907
Cite this article:	Walsh, David, Daly, Peter, "GPS and GLONASS Carrier Phase Ambiguity Resolution," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 899-907.
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