Implications of 30-Second Smoothing for GBAS Approach Service Type D

Tim Murphy, Matt Harris, Shelly Beauchamp

Abstract:	Development of Ground Based Augmentation System (GBAS) standards continues with the introduction of a new type of service intended to support the most demanding approach and landing operations in CAT III conditions. Proposed standards for this new service type have been drafted and are currently being validated. This new service type, called GBAS Approach Service Type D (GAST D) requires the use of code-carrier smoothing with a time constant of 30 seconds in addition to the codecarrier smoothing with a 100second time constant established by the original GBAS standards. This second smoothing time constant is used primarily as part of the mitigation of errors that could be induced by rare ionospheric anomalies. The ionospheric anomaly mitigations for GBAS have been discussed at length in other papers. However, the use of 30-second-smoothed pseudoranges has other implications on system performance such as some degradation in accuracy and also some effect on the availability of service. This paper considers these other implications of 30-second smoothing for GAST D and quantifies their effects. The error budget and accuracy performance for GAST D is examined given the requirement that the 30-second position solution be used to derive deviations for guidance. A theoretical derivation of the increase in noise is compared to bench and flight test data for both the airborne and ground segments with the 30-second smoothing applied. Thus, an expectation on the noise performance of a GAST D system is developed. Given that result, an expected availability of GAST D service is presented.
Published in:	Proceedings of the 2010 International Technical Meeting of The Institute of Navigation January 25 - 27, 2010 Catamaran Resort Hotel San Diego, CA
Pages:	376 - 385
Cite this article:	Murphy, Tim, Harris, Matt, Beauchamp, Shelly, "Implications of 30-Second Smoothing for GBAS Approach Service Type D," Proceedings of the 2010 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2010, pp. 376-385.
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