United States Department of Transportation
i
Status update on GPS integrity failure modes and effects analysis
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2004-01-01
[PDF-284.95 KB]
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Abstract:GPS integrity anomalies have long been of great concern to the civil and military GPS communities for safety-of- life operations. The FAA, USCG, and their international counterparts have focused on how to accomplish integrity monitoring for safety-of-life services through the use of receiver autonomous integrity monitoring (RAIM), widearea and local-area augmentation systems such as WAAS and LAAS, maritime differential GPS (DGPS) and nationwide differential GPS (NDGPS). The military is preparing to certify PPS RAIM receivers and is in the process of developing the Joint Precision Approach and Landing System (JPALS). Integrity failure modes need to be understood in order to develop a proper monitoring capability. The main objectives of the GPS Integrity Failure Modes and Effects Analysis (IFMEA) project are to identify GPS integrity monitoring requirements, examine GPS failure data in order to identify integrity failure modes, examine the causes and effects of the failures, as well as their probability of occurrence, determine the impact of integrity anomalies on users, and recommend preventive actions. The IFMEA project is focused on integrity anomalies that are due to hardware and software failures in the satellite vehicles (SVs) and Operational Control System (OCS). This paper provides a status update on the GPS IFMEA effort which is jointly funded by the Interagency GPS Executive Board (IGEB), the GPS Joint Program Office (JPO), and the Federal Aviation Administration (FAA). The IFMEA project began in 2002 under IGEB stewardship funding. Through the IFMEA project, Aberration Characterization Sheets (ACS) have been developed and updated for all GPS satellites through the Block IIR generation and work is now beginning on Block IIR-M, IIF, and the Architecture Evolution Plan (AEP) for the OCS. There is a need by those in the user community who are developing safety of life systems to be able to easily research GPS integrity anomaly data. In support of this effort, the IFMEA team is developing a database of all GPS service anomalies that can be accessed by type of anomaly, satellite number, satellite block affected, magnitude of error, date of occurrence, and duration of event. An effects analysis for WAAS and LAAS is being conducted to determine the impact on these augmentation systems from integrity anomalies. Finally, the IFMEA project is evaluating signal quality monitoring (SQM) algorithms to ensure proper detection of integrity anomalies and identify any design constraints or modifications to the GPS SV and OCS to either prevent failures that degrade integrity or provide protection from any adverse operational impact. This work is referenced in other ION papers [1] and [2]. The benefits of this work are to gain a better understanding of integrity anomalies, their probability of occurrence, and how to monitor for them. This information is essential to the design of differential GPS networks to support safety of life operations and will assist in meeting international commitments to describe GPS performance. The work performed under this study also will provide a technical basis to update the SPS and PPS Performance Standards and help develop recommendations for improvements to future GPS satellites and the operational control system.
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