High-Accuracy Point Positioning with Low-Cost GPS Receivers: How Good Can It Get?

Tomas Beran, Richard B. Langley, Sunil B. Bisnath and Luis Serrano

Abstract:	High-accuracy, point positioning has been an attractive research topic in the GPS community for a number of years. The overall quality of precise point positioning results is also dependent on the quality of the GPS measurements and user’s processing software. Dual-frequency, geodetic-quality GPS receivers are routinely used both in static and kinematic applications for high-accuracy point positioning. However, use of low-cost, single-frequency GPS receivers in similar applications creates a challenge because of how the ionosphere, multipath and other measurement error sources are handled. In this paper, we examine the potential use of such receivers to provide horizontal positioning accuracies of a few decimetres. Practical applications of post-processed, high-accuracy, single-frequency point positioning include a myriad of terrestrial and spaceborne applications, where the size and cost of the GPS unit is an issue. Our processing technique uses pseudorange and time-differenced carrier-phase measurements in a sequential least-squares filter. In developing our approach, we have attempted to separate and examine each measurement error, describe its properties and maximum error effect on the results, and implement algorithms to mitigate it. Ionospheric delay grid maps are used to remove the bulk of the ionospheric error, while tropospheric error is handled by a prediction model. Pseudorange multipath errors are mitigated by means of stochastic modelling and carrier-phase cycle slips are detected and corrupted measurements are removed in a quality-control algorithm. The technique was first tested on L1 measurements extracted from static datasets from static, high-quality GPS receivers. Accuracies better than two-decimetres in horizontal components (northing and easting r.m.s.), and three-decimetre accuracies in the vertical component (upcomponent r.m.s.), were obtained. A test dataset from a stationary low-cost GPS receiver has been processed to demonstrate the difference in data quality. Positioning results obtained are worse than those of a high-quality GPS receiver, but they are still within the few decimetre (dm) accuracy level (northing and easting r.m.s.). The use of the technique is not restricted to static applications, and the results of kinematic experiments are also presented.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1524 - 1534
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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