Flight Testing and Evaluation of Wide Area Differential GPS

Marie E. Lage and Bryant D. Elrod

Abstract:	The FAA is investigating the GPS Integrity Broad- cast/Wide Area Differential GPS (GIB/WADGPS) approach for augmenting GPS to meet integrity warning requirements and support Cat I or “near” Cat I precision approaches. A three phase program is underway to develop a testbed comprising: a network of monitor stations; a central processing facility to determine GPS integrity and differential correction data; a geostationary satellite (Inmarsat-2) to transmit “GPS-like” signals at L- band for GIB/WADGPS data distribution: and a user navigation package for tlight testing onboard an FAA test aircraft at FAATC. Phase I activities include testbed hardware integration and software development, preliminary WADGPS testing with a limited monitoring network (I 3 stations) and GPS integrity algorithm definition/assessment. Testing is progressing in four subphases: A. Static testing to checkout testbed hardware and interfaces. (Completed) B. Flight tests with a VHF GIB link to validate proto- type software and acquire preliminary GIB/WADGPS performance data (In progress) C. Dynamic testing with simulators providing GPS/GIB signals to validate receiver operations at L-band and related software. (TBD) D. Flight testing to assess GIB/WADGPS performance with the Inmarsat-2 GIB link and a monitoring network comprising one local and 3 remote stations 0-W. Preliminary Phase IB flight tests were conducted during early-mid afternoon in September 1992 at FAATC. The aircraft positioning performance (sensor accuracy) for WADGPS, L(ocal)DGPS and GPS only was analyzed along a - 6 nmi approach path at FAATC. The WADGPS results (based on a remote monitor station, 150 miles away) were within 1.5 meters per coordinate of LDGPS results at the 95% probability level on the basis of over 1800 data points acquired. Nevertheless, more extensive testing is required to validate WADGPS performance, since monitor station separations of 500 nmi or so are expected in a deployed system. Additional Phase IB testing is planned for January 1993. This paper will present an overview of the Phase I effort, the current testbed configuration, preliminary WADGPS flight test results and plans for further testing.
Published in:	Proceedings of the 1993 National Technical Meeting of The Institute of Navigation January 20 - 22, 1993 Parc 55 Hotel San Francisco, CA
Pages:	415 - 423
Cite this article:	Lage, Marie E., Elrod, Bryant D., "Flight Testing and Evaluation of Wide Area Differential GPS," Proceedings of the 1993 National Technical Meeting of The Institute of Navigation, San Francisco, CA, January 1993, pp. 415-423.
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