A Simple RAIM and Fault Isolation Scheme

R. Hatch, T. Sharpe, Y. Yang

Abstract:	The StarFire global DGPS system developed by NavCom for John Deere is able to provide 10 centimeter horizontal navigation anywhere in the world. This very high accuracy is obtained by using carrier-phase measurements with an effective floating ambiguity technique together with real-time orbit and clock corrections generated at the ground network processing hubs. In addition, the use of dual-frequency receivers allows the ionospheric refraction errors to be eliminated. The net result of these techniques is to yield a very accurate navigation solution together with very small post-fit measurement residuals, which are typically only a few millimeters. These small residuals allow a very simple but effective RAIM (receiver autonomous integrity monitoring) and fault isolation technique to be employed. The detection of a measurement problem is relatively straightforward. Any significant measurement errors, which occur after the initial floating ambiguities have converged, can be detected simply by monitoring the post-fix root-mean-square (rms) residuals. Any time five or more measurements are available, these post-fix residuals can be computed and, because they are normally so small, a problem can be detected quickly by testing to see if they exceed a few centimeters. When six or more satellites are available, a single measurement fault can be isolated to the proper satellite by computing the correlation coefficient between the measurement residuals and the appropriate row (or column) of the sensitivity matrix, S, whose construction is described. The satellite with the measurement fault will exhibit a correlation approaching a value of one. A derivation of the sensitivity matrix (S-matrix) and its use for this application are described. Sample results are presented.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	801 - 808
Cite this article:	Hatch, R., Sharpe, T., Yang, Y., "A Simple RAIM and Fault Isolation Scheme," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 801-808.
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