Rapid re-convergences to ambiguity-fixed solutions in precise point positioning |
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| Authors: | Jianghui Geng Xiaolin Meng Alan H Dodson Maorong Ge Felix N Teferle |
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| Institution: | (1) Western Australian Centre for Geodesy, Curtin University of Technology, GPO Box U1987, Perth, WA, 6845, Australia;(2) AAMHatch Pty Ltd, 23 Hamilton Street, Subiaco, WA, 6008, Australia;(3) Department of Mathematical Sciences and Technology, Agricultural University of Norway, P.O. Box 5003, 1432, Ås, Norway;(4) Geodetic Institute, University of Karlsruhe, Englerstrasse 7, 76128 Karlsruhe, Germany |
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| Abstract: | Integer ambiguity resolution at a single receiver can be achieved if the fractional-cycle biases are separated from the ambiguity
estimates in precise point positioning (PPP). Despite the improved positioning accuracy by such integer resolution, the convergence
to an ambiguity-fixed solution normally requires a few tens of minutes. Even worse, these convergences can repeatedly occur
on the occasion of loss of tracking locks for many satellites if an open sky-view is not constantly available, consequently
totally destroying the practicability of real-time PPP. In this study, in case of such re-convergences, we develop a method
in which ionospheric delays are precisely predicted to significantly accelerate the integer ambiguity resolution. The effectiveness
of this method consists in two aspects: first, wide-lane ambiguities can be rapidly resolved using the ionosphere-corrected
wide-lane measurements, instead of the noisy Melbourne–Wübbena combination measurements; second, narrow-lane ambiguity resolution
can be accelerated under the tight constraints derived from the ionosphere-corrected unambiguous wide-lane measurements. In
the test at 90 static stations suffering from simulated total loss of tracking locks, 93.3 and 95.0% of re-convergences to
wide-lane and narrow-lane ambiguity resolutions can be achieved within five epochs of 1-Hz measurements, respectively, even
though the time latency for the predicted ionospheric delays is up to 180 s. In the test at a mobile van moving in a GPS-adverse
environment where satellite number significantly decreases and cycle slips frequently occur, only when the predicted ionospheric
delays are applied can the rate of ambiguity-fixed epochs be dramatically improved from 7.7 to 93.6% of all epochs. Therefore,
this method can potentially relieve the unrealistic requirement of a continuous open sky-view by most PPP applications and
improve the practicability of real-time PPP. |
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