On Ultrahigh-Precision GPS Positioning and Navigation

Donghyun Kim and Richard B. Langley

Abstract:	In most GPS applications based on carrier-phase measurements, our first interest is to resolve the integer carrier-phase ambiguities because, once the ambiguities are fixed correctly, the carrier-phase measurements are turned into high-precision range measurements and hence it is possible to achieve centimetre-level positioning solutions. However, resolving the ambiguities is just one necessary step for high-precision positioning solutions. Correctly fixed ambiguities do not always guarantee centimetre-level positioning solutions due to errors in the carrier-phase measurements. In order to attain consistent high-precision positioning results with carrier-phase measurements, errors unspecified in the functional and stochastic models must be correctly detected and removed or otherwise handled at the data-processing stage. In this respect, reliability testing must be implemented as another necessary step for high-precision positioning solutions. We introduce in this paper an ultrahigh-performance GPS positioning and navigation system for gantry crane auto-steering. The system differs from conventional systems in terms of the positioning accuracy and precision it can achieve. Aside from ambiguity resolution and reliability, many error sources (such as phase wrap-up, antenna phase-center variation, instrumental group delay bias, receiver clock jumps, residual tropospheric delay, etc.) must be handled precisely to attain ultrahigh-precision positioning solutions. We also introduce an optimal inter- frequency carrier-phase linear combination of the L1 and L2 measurements which can reduce the effects of the quasi- random errors such as multipath, diffraction, ionospheric scintillation, etc. A practical approach to estimating realistic receiver system noise is also introduced.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	904 - 913
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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