Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and its Application to PPP

D. Laurichesse and F. Mercier

Abstract: Integer ambiguity resolution has been traditionally applied on double differenced phase measurements to achieve precise positioning of receivers antennas. This methodology is interesting because it removes most of the common errors between the different signal paths. It also minimizes the size of the problem to be solved by removing directly the clock contributions. However, double differencing creates a large number of short passes where there are only a few undifferenced passes. If common errors are known, it becomes attractive to solve directly integer ambiguities on the undifferenced measurements. In this case, the unambiguous phase measurement becomes a code-like measurement with a noise level lower than 1 cm. In this paper we present a new method for solving dual frequency GPS ambiguities on undifferenced measurements on a local or global network. Applications on precise point positioning (PPP) of a user receiver are also detailed. The problem is solved in two independent steps. -First, to eliminate unknown ionospheric propagation delays, undifferenced wide-lanes are estimated by a new approach. Validation using the differences with the obtained solutions is presented on various baselines, including space borne receivers, like the two formation-flying Grace satellites. -Second, we show how to estimate undifferenced ambiguities on L1 on a network of ground stations, once wide-lane ambiguities are known. The important point is to have a good initial modeling of the geometry in order to identify the integer ambiguities with a good confidence level. This initial modeling is given by a floating solution of the problem, in particular to obtain correct estimates of tropospheric delays. This complete process directly estimates around 90% of L1 elementary ambiguities on the entire network. Single or double differenced residuals show that the overall solution is correct. Finally, we show how to use the preceding results for an integer Precise Point Positioning of a moving ground receiver, relative to the reference network. The achieved performance is at the centimeter level. All the results presented in this paper are obtained through real data processing.
Published in: Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007)
September 25 - 28, 2007
Fort Worth Convention Center
Fort Worth, TX
Pages: 839 - 848
Cite this article: Laurichesse, D., Mercier, F., "Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and its Application to PPP," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 839-848.
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