Comparison of Continuity and Integrity Characteristics for Integrated and Decoupled Demodulation/Navigation Receivers

Jim Sennott and Dave Senffner

Abstract:	Signal fault events such as momentary blockages on low elevation satellites could jeopardize the continuity and integrity of GPS guidance. Classical receivers are especially vulnerablegiventheirisolatederrordetectors and loop filters for each channel. By contrast, an integrated receiver’s correlator data on all satellites is optimally tested and combined leading to a substantial suppression of cycle slippages during signal faults. The trade between continuity and integrity becomes more favorable with additional satellites/pseudolites. Provingthisassertionrequiredtheintegratedreceiver’s tracking performance be verified with differing signal geometries since, analogous to RAIM, performance is geometry dependent. The classical decoupled receiver structure is contrasted withthe integrated approach for a variety of geometries and signal faults. A signal fault continuity (SFC) definition is established encompassing accuracy and vertical protection limit (VPL) values to be satisfied during and immediately after signal fault events. Each satellite constellation is scanned to identify times of greatest vulnerability. In blockage testing geometries for which a sequential blockage on the two lowest elevation satellites couldlead to SFC loss areidentifled. In spoofing tests the disrupted satellite was selected on the basis of VPL maximization. In both blockage and spoofing tests the conventional receiver consistently loses continuity, whereas a high fraction of the time the integrated design provides seamless tracking, even with the difficult geometries. The impact of faults introduced at random times throughout the day is also ascertained, with substantial improvement for the integrated technique.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1531 - 1537
Cite this article:	Sennott, Jim, Senffner, Dave, "Comparison of Continuity and Integrity Characteristics for Integrated and Decoupled Demodulation/Navigation Receivers," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1531-1537.
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