The Importance of Code Measurements in Relative Positioning and Navigation

Daniel B. Sauer, Erwin Frei, Gefhard Beutler

Abstract:	High accuracies in relative positioning and differential navigation can be achieved using carrier phase measurements on one or, preferably, on both GPS carrier frequencies (Ll + L2). The code measurements play a subordinate role in these type of applications. Thus the analysis of code measurements together with phase measurements rarely attracts attention. The analysis of phase measurements is based on the assumption that the position the reference receiver is known in the WGS-84 coordinate system to better than 5 meters. If this basic requirement cannot be mef the final differential phase results will be biased. The biases introduced are dependent on the quality of the available initial positions. The cycle-slip detection process as well as the data screening process rely on the availability of an accurate absolute position for the reference site. If this position is not accurate enough, severe errors could be introduced, i.e. wrongly repaired cycle slips etc.. With SA now turned on, it is no longer possible to get absolute positions to the 5 to 15 meter accuracy level with just a few epochs of code measurements. The accuracies which can be achieved are more likely to be at the level of 50 to 250 meters. Thus special approaches and strategies are needed to handle relative positioning with phase measurements as far as the determination of position for the reference site is concerned. The paper first discusses robust methods to overcome the dil3iculties introduced by SA. Secondly, the benefits of combining code and phase measurements in kinematic applications are presented. The situation after a complete loss of lock is of special interest, because this relates directly to the task of resolving ambiguities on the fly.
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	1043 - 1051
Cite this article:	Sauer, Daniel B., Frei, Erwin, Beutler, Gefhard, "The Importance of Code Measurements in Relative Positioning and Navigation," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 1043-1051.
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