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Continuity
| Fundamentals | |
|---|---|
| Title | Continuity |
| Author(s) | Rui Barradas Pereira |
| Level | Basic |
| Year of Publication | 2011 |
The continuity of a system is the ability of the total system (comprising all elements necessary to maintain craft position within the defined area) to perform its function without interruption during the intended operation. More specifically, continuity is the probability that the specified system performance will be maintained for the duration of a phase of operation, presuming that the system was available at the beginning of that phase of operation[nb 1].
Failures and Continuity at GNSS constellation level
The description of the type of failures and its impact on continuity has been adapted from the GPS Standard Positioning Service (SPS) Performance Standard[2].
The types of failures can be grouped as:
- Hard Failures
- Wear-Out Failures
- Soft Failures
- Satellite O&M Activities
Hard Failures
This description has been adapted from the GPS Standard Positioning Service (SPS) Performance Standard Cite error: Closing </ref> missing for <ref> tag results in a loss of continuity or not depends on the Control Segment issuing a warning in advance of the signal interruption. If the nature of the hard failure is such that the Control Segment issues the warning in advance of the interruption, then there is no loss of continuity. If the hard failure results in a sudden or rapid loss of the signal from the satellite such that the Control Segment cannot issue a warning in advance, then there is a loss of continuity.
An alternate means of avoiding a loss of continuity exists in those situations where a second satellite occupies the same slot in the constellation. So long as the second satellite does not cease its signal transmissions, the sudden or rapid loss of the signal in either of the two satellites occupying that slot does not cause a loss of continuity.
Wear-Out Failures
This description has been adapted from the GPS Standard Positioning Service (SPS) Performance Standard Cite error: Closing </ref> missing for <ref> tag
The continuity is usually measured as the probability that the system performance is kept under the operational requirements during a certain amount of time.
Therefore common Continuity measurements are:
- %/h: Probability that the operational performance is kept over a one hour period.
- %/15s: Probability that the operational performance is kept over a fifteen seconds period.
Notes
- ^ This definition was adapted from the 2008 US Federal Radionavigation Plan[1]
References
- ^ US Federal Radionavigation Plan, DOT-VNTSC-RITA-08-02/DoD-4650.5, 2008
- ^ GPS Standard Positioning Service (SPS) Performance Standard, 4th Edition, September 2008.