Enabling the LAAS Differentially Corrected Positioning Service (DCPS): Design and Requirements Alternatives

Y.S. Park, S. Pullen, P. Enge

Abstract:	The Local Area Augmentation System (LAAS) can be used for both precision approach and Differentially Corrected Positioning Service (DCPS) applications. Through its support of DCPS, the LAAS Ground Facility (LGF) is required to meet the integrity requirements of all other operations that can receive the LAAS VHF Data Broadcast (VDB). Our previous work demonstrates that the DCPS integrity requirements cannot be met by the existing CAT I LAAS architecture without changes to both the definition of DCPS integrity and the airborne receiver requirements. This paper goes beyond our previous work in identifying the changes that are required and recommending specific sets of alternatives. Because the results of our previous work showed that having the worst-case ionosphere impact to any pair of satellites (as done for precision approach) cannot be supported for DCPS, this work limits the worst-case ionosphere impact to individual satellites. This represents one important but necessary change in the ionosphere anomaly threat model as applied to DCPS. Even with this change, the Maximum Unprotected Error, or MUE, is unacceptably high if no changes to the avionics requirements are made. Therefore, the results in this paper focus on various combinations of additional aircraft geometry screening and integrity monitoring to lower MUE to a usable level while maintaining useful DCPS availability. Two types of airborne geometry screening rules have been evaluated individually and in combination. The first rule limits airborne subset geometries by numbers of satellites used and the second rule limits the maximum absolute value of the range-to-horizontal-position scalar, |Shorizontal|. In addition, RAIM is evaluated to obtain additional reduction of MUE. Tables with results for the many alternatives tested are shown.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	1149 - 1158
Cite this article:	Park, Y.S., Pullen, S., Enge, P., "Enabling the LAAS Differentially Corrected Positioning Service (DCPS): Design and Requirements Alternatives," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 1149-1158.
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