Near-Term Integrity Improvements for the GPS Operational Control Segment

John V. Langer, William A. Feess, Ranwa N. Haddad, Michael D. Menn, Xuandzung T. Tran and Robert J. Lanahan

Abstract:	Future versions of the Global Positioning System may support significant levels of integrity, including a six second Time To Alarm (TTA) for an appropriately equipped user. The present system, on the other hand, has no integrity requirements other than a best effort by the Operational Control Segment (OCS) operators to correct misleading Signal In Space (SIS) issues as soon as possible. The “SVN 22 Event” of 2001, wherein a rogue satellite effectively broadcast incorrect information for nearly two hours, dramatically illustrated the extent of integrity risk in the current system. This paper outlines activities — planned and in progress — to improve the integrity of the current GPS signal. The activities fall into two principal categories: (1) detection of an erroneous SIS, and (2) mitigation of the error. After outlining the limitations of the current system, we introduce near-term improvements that will — in the event of a future erroneous SIS — reduce the user’s exposure time from hours to minutes. Specifically, we introduce a heterogeneous monitoring network that exploits current systems by the National Imagery and Mapping Agency (NIMA) , Jet Propulsion Laboratory (JPL) , the FAA’s Wide Area Augmentation System (WAAS) and others to provide timely alarms to the OCS. Analysis of alarms derived from data from these alternate resources is presented, along with a format for sharing integrity alarms among the different monitoring networks and the GPS system. We also discuss how these activities dovetail with the Global Dual-use Monitoring System (GDMS) initiative sponsored by the civil Interagency GPS Executive Board (IGEB), and how the concepts outlined in the paper can be extended from SIS integrity issues to more general integrity requirements for GPS.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1511 - 1518
Cite this article:	Langer, John V., Feess, William A., Haddad, Ranwa N., Menn, Michael D., Tran, Xuandzung T., Lanahan, Robert J., "Near-Term Integrity Improvements for the GPS Operational Control Segment," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1511-1518.
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