An Integrity, Availability and Continuity Test Method for EGNOS/WAAS

H. Kannemans

Abstract:	For safety of life applications of satellite navigation systems, in e.g. aviation, reliability in the sense of integrity, availability and continuity is essential. In order to test the integrity, availability and continuity, a test method is required. In practice, it is a requirement to be able to perform the analysis based on a limited amount of data collected within an acceptable observation time. This paper presents such a method for analyzing receiver output data of limited duration for SBAS. In the paper, a detailed discussion of the analysis of availability, integrity and continuity is given. The availability computation starts from the measured protection level data. It is possible to approach the protection level probability distribution by the Weibull distribution as will be shown in the paper. The HMI (Hazardous Misleading Information) probability depends on two basic parameters: the actual position error and the computed protection level. Usually one presents the test results in the so-called Stanford plots visualizing the occurrence of Hazardous Misleading Information. Since the probability of HMI is very low, it is not practical to state that the HMI probability is the ratio of the number of HMI results divided by the total number of measured samples. Very often, no HMI condition occurs during the tests; the resulting number of HMI conditions will then be zero and the computed HMI probability on this basis will then be zero as well, being obviously incorrect. Therefore, we need to invent a correct way in obtaining a realistic estimate of the HMI probability also called the integrity risk. The method developed for this purpose starts from the determination of two probability density functions: the probability density distribution of the protection level and a probability density function related to the position error, together forming a two dimensional probability density function. It is possible to compute the continuity risk (or noncontinuity) as function of the alert limit. It turns out the resulting non-continuity probability distribution can be approached by a lognormal distribution.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	882 - 893
Cite this article:	Kannemans, H., "An Integrity, Availability and Continuity Test Method for EGNOS/WAAS," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 882-893.
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