GPS-WAAS Static Error Analysis Using Wavelet Decomposition and Spectral Estimation

J.W. Dyer, V.E. DeBrunner, G. McCartor and J.E. Fagan

Abstract:	The residual error in the WAAS solution contains low frequency elements that reduce the accuracy of the vertical navigation during flight tests of precision approaches conducted at The University of Oklahoma. In an effort to determine if the WAAS-enabled GPS solution can be improved, the character of the errors was first determined. Static position error data from ten, geographically diverse, WAAS reference stations were initially collected continuously over the period of a month. A primary step in identifying the sources of error was to evaluate the spectral (periodic) content of the error signal. However, characterizing the spectral content of the error signal presents problems due to the extremely high sampling rate relative to the extremely slow periods of interest in the error signal. The WAAS signal was sampled at 1 Hz, yet the periods of interest are on the order of 10-5 Hz. Using our proposed method for extracting the near DC frequency content, it is shown that the WAAS residual error primarily contains periodic elements on the order of 6, 12, and 24 hours, which correspond to frequencies of approximately 4.6x10-5, 2.3x10-5, and 1.2x10-5 Hz, respectively. These results were consistent across the disparate geographic regions represented by the data set. Due to this, we think it unlikely that multi-path is responsible for these slow, periodic components in the residual error signal. Therefore, it is likely the periodic elements of the error signal are due primarily to the ionosphere.
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:	2385 - 2392
Cite this article:	Dyer, J.W., DeBrunner, V.E., McCartor, G., Fagan, J.E., "GPS-WAAS Static Error Analysis Using Wavelet Decomposition and Spectral Estimation," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2385-2392.
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