EGNOS Integrity from within. EGNOS CPF Processing Set Internal Check Function

Francisco Amarillo, Ignacio Delgado, Francisco Jose Jimenez

Abstract:	The key performance of SBAS systems, particularly of EGNOS, is the ability to preserve user integrity in the SBAS information. EGNOS approaches this goal through two elements providing Integrity evaluation. A specific element, the Central Processing Facility (CPF) Check Set is in charge of evaluating independently from the element providing the SBAS messages (the CPF processing Set), the integrity of the information provided to the user. In addition, even before the message is produced, the CPF Processing Set itself includes a battery of integrity evaluation functions with the goal of preventing misleading information from being generated. This paper presents the Internal Check Function of the CPF Processing Set. The function is composed of several components providing specific barriers against potential failure modes: •Inconsistencies in CPF internal data •Unstable or unpredictable behaviour of the information to be broadcast •Inconsistency between internal CPFPS information and the information broadcast to the user through the EGNOS GEO satellites •Lack of coherency between computed satellite and ionosphere corrections and their associated error bounds •Errors in intermediate corrections computation (e.g. tropospheric corrections) The function performs these tasks within strict environmental conditions as limited processing resources or time to alert requirements. It also has to maintain small rates of false alarm or missed detection events, and it is requested to provide fault isolation capability, down to the level of individual satellites or grid points. This paper presents the high level architecture of the Internal Check Function, providing a justification for its main functionalities. The paper describes the main objectives and means applied to each of those functionalities. Experimental results based on real and simulated data are presented to illustrate the level of reliability, which can be posed on the integrity of the data to be produced and broadcast by EGNOS. Key words: Integrity, EGNOS, Central Processing Facility.
Published in:	Proceedings of the 2001 National Technical Meeting of The Institute of Navigation January 22 - 24, 2001 Westin Long Beach Hotel Long Beach, CA
Pages:	638 - 647
Cite this article:	Amarillo, Francisco, Delgado, Ignacio, Jimenez, Francisco Jose, "EGNOS Integrity from within. EGNOS CPF Processing Set Internal Check Function," Proceedings of the 2001 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 2001, pp. 638-647.
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