Impacts of Ionospheric Fading on GPS Navigation Integrity

Gregory Bishop, Santimay Basu, Elizabeth Holland and James Secan

Abstract:	Rapid fading of GPS signals due to the ionosphere, which is caused by small-scale variations in ionospheric electron density, may produce a statistical reduction in satellite availability. Such fading is not usually thought to be significant to GPS navigation, since it is only observed at CONUS latitudes during severe geomagnetic storms, which may be years apart. However, such fading, does occur often over wide expanses of latitude bracketing the magnetic equator, and at the poles. These effects are particularly strong during the years of highest activity in the eleven year “solar cycle”. With the expansion of GPS navigation globally it is important to assess the potential for navigation impacts in the regimes where ionospheric fading is common. Reduction in satellite availability can occur when fades are of sufficient depth and duration to cause temporary loss of lock for an individual satellite being observed. Such losses could impact carrier-aided navigation and Receiver Autonomous Integrity Monitoring (RAIM) systems. Where the GPS antenna is desensitized at lower elevation angles to reduce multipath, ionospheric fading can produce a disproportionately greater impact on availability of satellites at lower elevations, thus raising the Geometric Dilution Of Precision (GDOP). We examine test data (antenna pattern, receiver dynamic range and fading occurrence at the equator and north polar regions) from a Trimble Pathfinder base station, and other GPS and L-band receivers, to make a first estimate of the degree and occurrence of impacts for these equipments. We outline an approach to assessing the potential for impact and predicting system performance in specific GPS applications, using existing models of ionospheric fade occurrence.
Published in:	Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT
Pages:	577 - 585
Cite this article:	Bishop, Gregory, Basu, Santimay, Holland, Elizabeth, Secan, James, "Impacts of Ionospheric Fading on GPS Navigation Integrity," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 577-585.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In