Performance of Network RTK Using Fixed and Float Ambiguities

A.B.O. Jensen and M.E. Cannon

Abstract:	Real time kinematic differential GPS positioning (RTK) at the cm–level is generally carried out using real time data from only one reference receiver. Current research activities have shown, however, that the performance of RTK positioning can be improved considerably over longer baselines if differential phase corrections are generated based on a network of reference stations. These analyses show positioning accuracies better than 10 cm. This level of accuracy has been obtained only when L1 phase ambiguities for the baselines between the stations in the reference network have been solved to fixed integer values. This paper focuses on the use of float ambiguities for the reference station vectors in the network. Float ambiguities are being investigated since it can be difficult to resolve the integer ambiguities efficiently and reliably in real time over a network with baseline lengths of typically 40 to 200 km. Based on GPS data from a number of reference stations the ambiguities for the baselines in the reference network are determined as both fixed and float values. Data from the reference stations are used along with either the fixed or float ambiguities to generate phase corrections by utilising a new method developed at the University of Calgary. Positioning of a user receiver is carried out employing the corrected phase data and conventional GPS positioning software. Various scenarios are evaluated whereby the ambiguities are solved to either fixed or float numbers, and using both single and dual frequency GPS data. The results are analysed emphasising on the positioning accuracy, and it is concluded that the accuracy over 24 hours is of about the same level if using fixed or float ambiguities. Finally the method is evaluated for eventual real time use.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	797 - 805
Cite this article:	Jensen, A.B.O., Cannon, M.E., "Performance of Network RTK Using Fixed and Float Ambiguities," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 797-805.
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