Transient Performance Analysis of a Multicorrelator Signal Quality Monitor

R. Eric Phelts, Alexander Mitelman, Sam Pullen, Dennis Akos and Per Enge

Abstract:	The ability to monitor and detect problematic distortions in the received GPS-SPS signal is a task of critical importance. Detection of these satellite signal anomalies or “evil waveforms” (EWFs) can be accomp lished using detailed monitoring of the correlation peak. Using the proposed “2nd-Order Step” (2OS) Threat Model for evil waveforms, previous analysis has shown that, in steady state, monitoring sufficient to satisfy GBAS and SBAS requirements for Category I precision approaches may be obtained from a receiver design that requires minimal modifications to existing GPS hardware. In other words, ignoring time-to-alarm requirements, it has been shown that these anomalous waveforms can be detected using a practical, multicorrelator SQM implementation—defined as SQM2b. The ability of the monitor receiver to detect hazardous evil waveforms within the time to alarm, however, is necessary to guarantee airborne users never experience hazardously misleading information. This paper shows that, without modification, SQM2b (previously validated by steady-state analysis alone) does not promptly mitigate this integrity threat. Further, it suggests that modifying the smoothing filter for the detection metrics can slightly decrease the response time required by the monitor detect these waveforms. More significantly, leveraging the same measurements taken from SQM2b, it introduces an additional nonlinear detection test that improves the sensitivity of the monitor to detectable anomalous waveforms. The paper presents analytical results which verify that these modifications can detect the hazardous waveforms within the 6-second timeto- alarm required by LAAS. Finally, it validates the performance of this test using experimental data taken from a real-time evil waveform-generating hardware.
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:	1700 - 1710
Cite this article:	Phelts, R. Eric, Mitelman, Alexander, Pullen, Sam, Akos, Dennis, Enge, Per, "Transient Performance Analysis of a Multicorrelator Signal Quality Monitor," 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. 1700-1710.
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