ENAC 8 th March 2018 RAMS FOR GNSS
- Slides: 26
ENAC |8 th March 2018 RAMS FOR GNSS Carl Milner– ENAC Assistant Professor in the TELECOM Group
QUESTIONS • How to relate the Tolerable Hazard Rate per hour to the positioning function per epoch/sample/test? – • What conditions may be defined around the use of GNSS in rail? – – • Correlation time impacts (Fault Free case and Faulty case) Is there a known probabilistic distribution for them? average risk Is there reasonable means to predict? specific risk How to measure/ensure maintainability for GNSS applications? WP 1 Brainstorming 2 Webex, 12/02/2018
RAMS VS GNSS SIS - Positioning, Navigation and Timing (PNT) - In aviation, the active Navigation System provides the primary guidance function. - Navigation System Error (NSE) is then the difference between the true position and estimated position. - Signal-In-Space (SIS) performance requirements express the quality of a GNSS PNT service assuming a fault-free receiver, meaning one which is operating nominally - SIS performance includes nominal errors which are local to the aircraft, namely multipath and receiver noise which have been modelled and validated by Boeing (Wozniak, 1997) and Airbus shall meet the 2010) “ 3. 7. 2. 4. 1 The combination of GNSS elements and a fault-free GNSS user receiver signal-in-spacerequirementsdefinedin. Table 3. 7. 2. 4 -1”(ICAOSARPS, WP 1 Brainstorming 3 Webex, 12/02/2018
RAMS VS GNSS SIS Safety Risk Navigation System Safety Risk SIS Safety Risk from Aircraft Failure WP 1 Brainstorming RX 4 Webex, 12/02/2018
RAMS VS GNSS SIS Safety Risk Navigation System Safety Risk SIS Safety Risk from Aircraft Failure WP 1 Brainstorming RX 5 Webex, 12/02/2018
RAMS VS GNSS SIS - SIS Requirements - Accuracy - WP 1 Brainstorming 6 Webex, 12/02/2018
RAMS VS GNSS SIS - SIS / PNT Requirements - WP 1 Brainstorming 7 Webex, 12/02/2018
RAMS VS GNSS SIS - SIS / PNT Requirements - Continuity - Availability - Reliability Continuity of a system is the ability of the system to perform its function without interruption during the intended operation i. e. the probability that the specified performance will be maintained for the duration of a phase of operation “The continuity requirement should be applied as applying the average risk of loss of service” The percentage of time that the services of a system are available (accuracy and integrity are met, in some interpretations also continuity) The probability that a system will perform its function within defined performance limits for a specified period of time (not the operation duration) WP 1 Brainstorming 8 Webex, 12/02/2018
RAMS VS GNSS SIS WP 1 Brainstorming 9 Webex, 12/02/2018
RAMS VS GNSS SIS • WP 1 Brainstorming 10 Webex, 12/02/2018
RAMS VS GNSS SIS • WP 1 Brainstorming 11 Webex, 12/02/2018
RAMS VS GNSS SIS WP 1 Brainstorming 12 Webex, 12/02/2018
RAMS VS GNSS SIS • WP 1 Brainstorming 13 Webex, 12/02/2018
RAMS VS GNSS SIS - System States Available + Safe <THR ? ‘Failed’/ Unavailable/ Outage Available + Unsafe WP 1 Brainstorming 14 Webex, 12/02/2018
RAMS VS GNSS SIS - First Mapping WP 1 Brainstorming 15 Webex, 12/02/2018
RAMS VS GNSS SIS • WP 1 Brainstorming 16 Webex, 12/02/2018
RAMS VS GNSS SIS - Alert Limit – no agreement: - - 2. 5 m for track discrimination/station operations 20 -25 m for along-track positioning or might also be expressed as a function of speed Time-to-alert – values between 1 s and 5 s WP 1 Brainstorming 17 Webex, 12/02/2018
RAMS VS GNSS SIS - What would be the response of the rail network to a ‘Predictable’ outage? - Continuity in aviation is a safety issue vs. Reliability in RAMS is not - Reliability and Availability are directly linked in RAMS - The PNT service is available in civil aviation even if an aircraft experiences a loss of continuity (standard interpretation) - Predictable outages are not continuity risks (not universal agreement on interpretation, depends upon system development - Navigation systems may be sole/primary/supplemental means - - Mitigations for loss of service Since global availability and probability of a down state switch depend upon many factors (including the solution proposed), the requirement used for detection thresholds (continuity) should be set late WP 1 Brainstorming 18 Webex, 12/02/2018
RAMS VS GNSS SIS - Loss of Reliability (Failures) - Immobilising Service Minor WP 1 Brainstorming 19 Webex, 12/02/2018
RAMS VS GNSS SIS WP 1 Brainstorming 20 Webex, 12/02/2018
RAMS VS GNSS SIS - Loss of Availability/Continuity - Predictable - - Slow geometry change increased protection level (or real time integrity risk) unavailable time repair Satellite loss passing horizon increased protection level unavailable time repair Satellite loss due to planned manoeuvre/maintenance (NANU warning) increased protection level unavailable time control repair Masking loss of tracking geometry change increased protection level unavailable location user repair Unpredictable - False alarm failed exclusion unavailable time repair Satellite failure correct detection failed exclusion unavailable time control repair Ionosphere gradient correct detection failed exclusion unavailable time repair Extreme multipath correct detection failed exclusion unavailable time repair Interference loss of tracking geometry change increased protection level unavailable time repair Jamming loss of tracking geometry change increased protection level unavailable time security repair Scintillation loss of tracking geometry change increased protection level unavailable time repair Shadowing loss of tracking geometry change increased protection level unavailable time user repair Change in error models (i. e. from DGNSS) increased protection level unavailable time user repair WP 1 Brainstorming 21 Webex, 12/02/2018
RAMS VS GNSS SIS • WP 1 Brainstorming 22 Webex, 12/02/2018
WP 1 RAMS VS SIS/PNT • WP 1 Brainstorming 23 Webex, 12/02/2018
WP 1 RAMS VS SIS/PNT • WP 1 Brainstorming 24 Webex, 12/02/2018
WP 1 RAMS VS SIS/PNT • WP 1 Brainstorming 25 Webex, 12/02/2018
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 777561 Call identifier: H 2020 -S 2 RJU-2017 Topic: S 2 R-OC-IP 2 -01 -2017 – Operational conditions of the signalling and automation systems; signalling system hazard analysis and GNSS SIS characterization along with Formal Method application in railway field
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