Evil Waveforms in Stand-Alone GPS Aviation Applications

Gary Brodin, Andrew Cartmell, David Walsh, Mark Denney and Steve Griffin

Abstract:	The use of GPS in aviation applications continues to increase. GPS is currently certified by the UK CAA for use in basic area navigation (B-RNAV) operations and oceanic/remote operations, whilst use for precision area navigation (P-RNAV) and non-precision approaches (NPAs) may also soon be notified. The CAA’s Safety Regulation Group (SRG) is responsible for approval of all UK air traffic services. As part of SRG’s hazard analysis into the use of GPS the CAA-ISN is currently performing a GPS monitoring programme to determine if GPS performs to standards and if not what are its failure modes. As accuracy and integrity requirements increase the performance of the avionics GPS receiver becomes increasingly important in this hazard analysis. The performance of the receiver under anomalous signal conditions is of particular concern. This paper presents the analysis that has been performed by the CAA-ISN for SRG to determine the range of receiver architectures that could be used to meet current aviation standards. The effects of differing architectures on the tracking errors produced by anomalous signals, known as Evil Waveforms (EvWFs), on stand-alone GPS receivers have also been determined and are presented. The paper begins by determining the wide range of receiver architectures that could be used to meet the current standards for GPS aviation receivers operating in UK airspace. FAA TSO-C129 is the basis of approval of such GPS receivers; it is however a very open standard in terms of receiver architectures. The acquisition and tracking requirements of TSO-C129 have been used to identify the range of architectures that could be in use in current certified receivers. The implications of open standards for GPS avionics receivers are demonstrated by presenting the effects of EvWFs on different stand-alone receiver architectures. The range errors caused by EvWFs are highly dependent on receiver architecture. The relationship between receiver architecture and the resultant stand-alone range errors are presented. The paper concludes by presenting typical horizontal position errors that could be produced by EvWFs in an aircraft operating at B-RNAV minimum height in UK airspace.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	2376 - 2385
Cite this article:	Brodin, Gary, Cartmell, Andrew, Walsh, David, Denney, Mark, Griffin, Steve, "Evil Waveforms in Stand-Alone GPS Aviation Applications," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 2376-2385.
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