Sensitivity Analysis of Code Carrier Divergence Monitor Algorithms

Youngsun Yun, Jeongho Cho and Moon-Beom Heo

Abstract:	Ground Based Augmentation System (GBAS) has been developed to support aircraft precision approaches based on Global Positioning System (GPS). Since GPS faults and anomalies could lead integrity risk of the airborne systems, GBAS ground stations continuously monitor integrity threats to exclude them or alert airborne users within a required time-to-alarm. Code carrier divergence (CCD) due to GPS satellite fault or ionosphere anomaly is one of the threats specified by international standards, so a couple of CCD monitor algorithms have been proposed by researchers and implemented in GBAS ground facilities and airborne systems. Those are the first and the second order linear time invariant filters with various time constants. The first order filter with a time constant of 200 seconds has been proposed for the ground and airborne CCD monitors. In order to employ the second order filters that need two time constants, 25 or 30 seconds have been set by the ground stations and 100 seconds by the airborne equipment. In all these cases, the two time constants have been set to be identical for simplicity. This paper investigates the code carrier divergence detection sensitivity to the monitor time constants so as to find the optimal parameter combination. Theoretical and empirical analysis on the filters with different time constants values and combinations demonstrates the filter stability and response to the CCD failure. The results show that the ground stations can employ smaller time constants than the legacy values without loss of integrity under multipath limited condition and need careful investigation under severe multipath condition. The paper also proposes integrity margin as a performance index for optimal monitor configuration determination.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3505 - 3511
Cite this article:	Yun, Youngsun, Cho, Jeongho, Heo, Moon-Beom, "Sensitivity Analysis of Code Carrier Divergence Monitor Algorithms," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 3505-3511.
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