Ambiguity Pseudo-fixing in Precise Single Point Positioning

X. Shen and Y. Gao

Abstract:	Carrier phase based precise single point positioning (PPP) usually require 30 minutes and 2 hours for the float ambiguity parameters to converge respectively for static and kinematic processing. To reduce the convergence time and apply PPP method to real-time applications, ambiguity-fixing methodology must be developed. This paper describes the development of an ambiguity pseudo-fixing method for PPP applications. Different from conventional double differenced ambiguity resolution, the un-differenced ambiguity parameter in a PPP model contains a non-integer initial phase component whose magnitude, however, always less than one full cycle of the phase wavelength. As a result, the ambiguity resolution process in PPP is to fix the ambiguity parameter to the nearest integer or a float value of its true value – a pseudo-fixing concept. Decimeter positioning accuracy can be ensured if the fixing is successful. The conventional way to validate a successful ambiguity set is to test the ratio of the smallest and second-smallest sums of the squared observation residuals. As the ambiguities in PPP are originally non-integer, a test on two ambiguity pairs with the smallest and the second smallest should be used along with other test criteria such as residual check, variance adjustment, and etc. A partialfixing approach, which fixes one satellite at a time, has been implemented with a sequential filter used to propagate variance-covariance information of the unknown parameters from epoch to epoch. To assess the performance of the proposed method, numerical calculation and analysis have been conducted using observations from one IGS station. The preliminary results have shown that the obtainable positioning accuracy is in decimeter within a few minutes both in static and kinematic mode after the ambiguity is fixed.
Published in:	Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002) June 24 - 26, 2002 Hyatt Regency Hotel Albuquerque, NM
Pages:	163 - 168
Cite this article:	Shen, X., Gao, Y., "Ambiguity Pseudo-fixing in Precise Single Point Positioning," Proceedings of the 58th Annual Meeting of The Institute of Navigation and CIGTF 21st Guidance Test Symposium (2002), Albuquerque, NM, June 2002, pp. 163-168.
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