Pulsed RFI Effects on Aviation Operations Using GPS L5

R. J. Erlandson, T. Kim, C. Hegarty and A. J. Van Dierendonck

Abstract:	In mid- to high altitude operations, the aviation GPS L5 receiver is exposed to a unique electromagnetic environment created by existing aeronautical system pulsed emitters. These include: ground-based TACAN and DME beacon transponders (many within the L5 band); military JTIDS/MIDS system terminals (spread- spectrum, overlapping L5); on-board and nearby ATC aircraft avionics, and ground ATC SSR interrogators; and on-board and nearby TACAN/DME interrogators (with potential receiver front-end saturation effects). An initial 1999 study commissioned by the US Inter-agency GPS Executive Board (IGEB) [1, 2] showed large degradations to the L5 receiver carrier-to-noise density ratio from the composite pulsed RFI environment at high altitudes over several hot-spots in the US, Europe, and Japan. At that time the most likely means of RFI mitigation seemed to be reducing the number of in-band DME/TACAN ground beacons (e.g., by changing the channel frequency). Subsequent work suggested that RFI mitigation in L5 receiver may also be a feasible option. In late 1999 RTCA was tasked by the US Department of Transportation to review and extend the IGEB initial study. DOT requested an updated assessment of the RFI environment around the GPS L5 frequency band (1176.45 ± 10 MHz), appropriate L5 receiver susceptibility criteria and pertinent RFI source mitigation recommendations. Delayed by two years to address higher priority GPS L1 RFI issues, the RTCA L5 RFI assessment effort re-started in late 2002 and is nearly complete as of this writing. This paper1 presents the analyses of two of the nine operational scenarios examined by RTCA SC-159 WG-6: high altitude (40,000 ft.) operation over the worst US hot- spot and transition altitude (1600 ft) operation near the final approach fix waypoint to Washington Reagan National Airport Runway 4. An updated analytical analysis approach is developed. A feasibility model receiver is proposed. RFI sources are characterized and receiver performance assessed in RFI link analyses for the two scenarios.
Published in:	Proceedings of the 2004 National Technical Meeting of The Institute of Navigation January 26 - 28, 2004 The Catamaran Resort Hotel San Diego, CA
Pages:	1063 - 1076
Cite this article:	Erlandson, R. J., Kim, T., Hegarty, C., Van Dierendonck, A. J., "Pulsed RFI Effects on Aviation Operations Using GPS L5," Proceedings of the 2004 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2004, pp. 1063-1076.
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