GPS Interference Source Location and Avoidance Systems

Bette M. Wirier, Paul Manning, E. Michael Geyer, Joseph Ruggiero and Philip McCarty

Abstract:	Due to the planned high reliance on GPS for aviation applications, if a radio frequency interference (RFI) incident does occur, the rapid location and removal of the source will be essential. Such rapid response capability requires widespread deployment of the field detection instrumentation. Achieving wide- spread deployment at reasonable costs requires the development of new approaches to source location. When a rare report of interference is received, these systems must be operable by non-specialists with minimal training. The U.S. DOT Volpe National Transpoitation Systems Center (Volpe Center), under the sponsorship of the Federal Aviation Administration, is currently developing two innovative instruments for locating sources of RF1 to GPS. A GPS Interference Locator System (GILS) is intended primarily for use by personnel on the ground; it uses the traditional RF1 localization technique involving a directional antenna and signal detection electronics. However, achieving low-cost and simplicity of operation while still being able to sense the low signal levels that can disrupt GPS necessarily entails compromises. This paper describes the four design approaches formulated for GILS, discusses the tradeoffs, and presents the results of tests performed on a system prototype. The fundamental “instruments” for measuring the direction of a GPS interference source from an aircraft (ARLAS -- Aircraft RI?1 Localization and Avoidance System) is the vertical (elevstion) pattern of the aircraft’s top-mounted GPS antenna, the signal-to-noise ratio (SNR) that can be calculated by every GPS receiver and the values of roll, pitch and heading from aircraft gyros. When the aircraft is bank& the antenna illuminates some areas on the ground (low SNR if interferer is present) while obscuring others (higher SNR even if intetierer is present). By flying in a tight circle, the aircraft effectively “scans” the ground and obtains data sufficient to estimate the direction of an RF1 source. The design approach is demonstrated using data from the 1994 St. Louis GPS anomaly. The ARLAS system being developed for the FM would use data from equipment already deployed on FAA aircraB, merely adding a software module to the flight management system. In this way, every FAA aircraft can be used to locate RF1 sources at minimal cost. If added to GPS receiver software, it could assist non-FAA aircraft to provide the FAA with more precise reports of RF1 events and to avoid airspace effected by RF1 (should it occur). It will also distinguish between RF1 from environmental or on-site sources.
Published in:	Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997) June 30 - 2, 1997 Albuquerque, NM
Pages:	69 - 77
Cite this article:	Wirier, Bette M., Manning, Paul, Geyer, E. Michael, Ruggiero, Joseph, McCarty, Philip, "GPS Interference Source Location and Avoidance Systems," Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997), Albuquerque, NM, June 1997, pp. 69-77.
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