Optimizing Channel Selection for the JPALS´ Land-based Integrity Monitor

Michael Koenig, Jason Rife, Sam Pullen and Per Enge

Abstract:	JPALS (Joint Precision Approach and Landing System) is a precision landing system that provides LAAS (Local Area Augmentation System) like capabilities in a military operating environment. This paper discusses the landbased JPALS application and the enhancement of a selection algorithm called EXM (Executive Monitor). The EXM examines the pass/fail outputs of other monitors to define a common set of data based on exclusion of detected satellite or receiver faults. Prior versions of the EXM used heuristic rather than optimal criteria. Using data collected from Stanford´s LAAS IMT prototype, we evaluated the EXM algorithms with an analysis tool called the JTEP (JLIM Test Platform), where JLIM stands for the JPALS Land-based Integrity Monitor. The VPL (Vertical Protection Limit) is a high-integrity estimation of the landing aircraft’s vertical positioning error. It is a function of satellite geometry, the number of receivers, and the quality of each satellite’s ranging signal. When the VPL is below the VAL (Vertical Alarm Limit) the landing system is available. Our paper shows that an EXM decision method based on minimizing the VPL provides greater availability than previously achieved. The traditional method of defining a common set by maximizing the number of receivers is less complex to code and less computationally demanding than the VPL based method. However, our results show the VPL method provides better availability performance with sufficient computational efficiency to enable real-time operation. To establish the performance benefits of the VPL-based method, this paper presents two analyses. The first details a comparison of EXM decision logic for the all-in-view satellite case. The second shows the robustness of VPLbased algorithms to a degraded one-satellite out case. The degraded constellation reflects a user aircraft which is unable to track all the satellites, an even which may occur commonly in JPALS due to jamming, interference, or aerial maneuvers (obstruction).
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	62 - 72
Cite this article:	Koenig, Michael, Rife, Jason, Pullen, Sam, Enge, Per, "Optimizing Channel Selection for the JPALS´ Land-based Integrity Monitor," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 62-72.
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