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Galileo Integrity Monitoring
| GALILEO | |
|---|---|
| Title | Galileo Integrity Monitoring |
| Author(s) | ESA |
| Level | Basic |
| Year of Publication | 2010 |
The GALILEO System will be an independent, global, European-controlled, satellite-based navigation system and will provide a number of guaranteed services to users equipped with Galileo-compatible receivers. One of these services is the GALILEO Safety-of-Life Service (SoL) which improves the open service performance through the provision of timely warnings to the user when it fails to meet certain margins of accuracy (integrity). [1]
Purpose
The target markets of the Safety of Life service are safety critical users whose applications or operations require stringent performance levels such as running trains, guiding cars, navigation and aviation. Galileo will provide to its users not only a global positioning service (Open Service), but also the associated integrity information for SoL services. This is an important contribution of Galileo against the GPS or GLONASS systems, where the SoL integrity must be provided by augmentation systems (WAAS, EGNOS...).
Performance and features
In comparison with other regional services (WASS, EGNOS…) provided by traditional ground infrastructures, Galileo SoL Service will provide integrity information at global level. A worldwide seamless service will increase the efficiency of companies operating in a global basis, e.g. airlines, transoceanic maritime companies.
With regard to Safety of Life Services, there are certain levels of service that are stipulated by lawin various international transportation fields, and other that are recommended practices (e.g.Standards and Recommended Practices -SARPS- by ICAO). A very specific level of service from Galileo will be needed to comply with legislation applicable for all considered domains of transport and existing standards.
The Safety of Life service will be provided globally according to the performances indicated in the table below. These specifications include two levels to cover two conditions of risk exposure [2]:
- The Critical level covers time critical operations for example, in the aviation domain approach operations with vertical guidance.
- The Non-Critical level covers extended operations that are less time critical, such as open sea navigation in the maritime domain
The critical level will be obtained by using certified dual-frequency receivers in the following frequencies:
- E5b and L1.
- E5a, E5b and L1
Whereas Non-Critical level will be possible to obtain by using monofrequency receivers in the bands E5b or L1.
According to Galileo Requirements Document the SoL multi frequency service in the critical level shall provide:
- Horizontal Accuracy <= 220 m (NSE- 95%)
- Integrity Risk <= 10-7 per hour
- Mean Availability over the operational life of at least 99.5 % for integrity and 99.8 % for accuracy for any location within the default service volume. (HAL 12m, VAL 20m)
With regard to the non critical level, the SoL multi frequency and mono frequency service in the critical level shall provide:
- Horizontal Accuracy <= 4 m (NSE- 95%) and a Vertical Accuracy <= 8 m (NSE - 95%).
- Integrity Risk <= 3.5.10-7 per period of 150s
- Mean Availability over the operational life of at least 99.5 % for integrity and 99.8 % for accuracy for any location within the default service volume. (HAL 556m) TBC
The performance objectives in terms of position accuracy, availability and integrity are described in the following table [2]:
| Galileo Safety of Life Service | |||
|---|---|---|---|
| Coverage | Global | ||
| Critical Level | Non-critical Level | ||
| Accuracy (95%) | Horizontal: 4 m | Horizontal: 220 m | |
| Vertical: 8 m | |||
| Integrity (95%) | Alarm Limit | H: 12 m, V: 20 m | H: 220 m |
| Time-To-Alarm | 6 seconds | 10 seconds | |
| Integrity Risk | 3.5x10-7/150s | 10-7/hour | |
| Continuity Risk | 10-5/15s | 10-4/hour - 10-8/hour | |
| Certification/Liability | Yes | ||
| Availability of Integrity | 99.5 % | ||
| Availability of accuracy | 99.8 % | ||
To know more information about Performances of each Galileo Service see the article Galileo Performances.
Implementation
The Safety of Life Service signals are separated in frequency to improve robustness to interference and to permit correction of errors induced by ionospheric effects by differentiation of the ranging measurements made at each frequency. Each navigation frequency will include two ranging code signals (in-phase and quadrature). Data are added to one of the ranging codes while the other “pilot” ranging code is data-less for more precise and robust navigation measurements. The integrity data will be broadcast in the L1 and E5b bands [2]. It has to be noted that the Galileo Safety of Life frequencies are in Aeronautical Radio-Navigation Service (ARNS) bands allocated for GNSS. The integrity broadcast and the protection provided in the ARNS bands are two important features of the Galileo SoL.
This service will be offered openly and the system will have the capability to authenticate the signal (e.g. by a digital signature) to assure the users that the received signal is the actual Galileo signal. The system will have the capability to activate or deactivate this feature that shall be transparent and nondiscriminatory to users and shall not introduce any degradation in performances [3]
Notes
References
- ^ ESA Galileo web page
- ^ a b c Galileo Mission High Level Definition, v3, September 2002.
- ^ GALILEO Mission Requirements Documment, Issue 5 – Draft