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Galileo Integrity Monitoring
| GALILEO | |
|---|---|
| Title | Galileo Integrity Monitoring |
| Edited by | GMV |
| Level | Basic |
| Year of Publication | 2011 |
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, for which the SoL integrity must be provided by augmentation systems (WAAS, EGNOS…).
Performance and features
In comparison with other regional services provided by traditional ground infrastructures (WAAS, EGNOS…), Galileo SoL Service will provide integrity information at global level that will allow system failures to be reported to the users. A worldwide seamless service will increase the efficiency of companies operating in a global basis, such as airlines or transoceanic maritime companies. This service will be certified against applicable standards and performance.[2]
The SoL distinguishes two level of service provisioning to cover two conditions of risk exposure:[3]
- The Critical level covers time critical operations for example, in the aviation domain approach operations with vertical guidance. It will be obtained by using certified dual-frequency receivers in the bands E5a, E5b and L1.
- The Non-Critical level covers extended operations that are less time critical, such as open sea navigation in the maritime domain. It will be obtained by using certified dual-frequency receivers and also mono-frequency receivers in the bands E5b or L1
The performance objectives in terms of position accuracy, availability and integrity for Critical and Non-Critical Level are described in the following table [3]:
| 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 [3]. 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[4].
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 non-discriminatory to users and shall not introduce any degradation in performances.[3]
Unlike the Open Service, the Public Regulated Service and the Search-And-Rescue Service, the Safety of Life Service will not be available during the Initial Operational Capability (IOC) phase. Moreover, the requirements of Galileo's SoL service are having an impact on the programme's funding needs, particularly with regard to the ground infrastructure. Studies to redefine this service are under way in order to adapt it to the new user needs and new technological developments[5].
Notes
References
- ^ ESA Galileo web page
- ^ Galileo Services on GSA official website
- ^ a b c d Galileo Mission High Level Definition, v3, September 2002.
- ^ Avila-Rodriguez, J.A., Hein, G.W. et al., "The MBOC Modulation: The Final Touch to the Galileo Frequency and Signal Plan"; Proceedings of ION GNSS 2007, Fort Worth, Texas, USA, 25-28 September 2007
- ^ Mid-term review of the European satellite radio navigation programmes