More Ionosphere Anomaly Mitigation Considerations for Category II/III GBAS

T. Murphy and M. Harris

Abstract:	Standards are being developed to enable Ground Based Augmentation Systems (GBAS) to support Category II and Category III (CAT II/III) operations. An example of GBAS is the FAA’s Local Area Augmentation System (LAAS). Previous work has shown that ionospheric anomalies can occur as a result of solar storms. These anomalies can cause non-negligible errors in a GBAS system. This has been an active area of research for a number of years and strategies for the mitigation of these types of errors have been investigated. Solutions for mitigation of potential errors due to an ionospheric anomaly have been proposed and the supporting analysis has matured. This paper describes a mitigation strategy that is proposed for inclusion in the standards for GBAS. The paper provides theoretical background and gives results of analysis done in support of validation of the mitigation strategy. Analyses on performance of various geometry screening and ionosphere gradient detection schemes have been performed using flight test data processing and using modeling and simulation. Results from these analyses are presented. Practical thresholds for airborne and ground monitoring of code carrier divergence are discussed. Finally, the performance of the combination of airborne and ground monitoring is evaluated and the ramifications with respect to system level performance are discussed.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	438 - 452
Cite this article:	Murphy, T., Harris, M., "More Ionosphere Anomaly Mitigation Considerations for Category II/III GBAS," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 438-452.
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