If you wish to contribute or participate in the discussions about articles you are invited to contact the Editor
Galileo Performances
| GALILEO | |
|---|---|
| Title | Galileo Performances |
| Edited by | GMV |
| Level | Basic |
| Year of Publication | 2011 |
Galileo system is a space-based global navigation satellite system (GNSS) that provides reliable positioning, navigation, and timing services to users on a continuous worldwide basis. The Galileo system, once fully operational, will offer four high-performance services worldwide:
- Open Service (OS): Galileo open and free of charge service set up for positioning and timing services.
- High Accuracy Service (HAS): A service complementing the OS by providing an additional navigation signal and added-value services in a different frequency band. The HAS signal can be encrypted in order to control the access to the Galileo HAS services.
- Public Regulated Service (PRS): Service restricted to government-authorised users, for sensitive applications that require a high level of service continuity.
- Search and Rescue Service (SAR): Europe´s contribution to COMPAS-SARSAT, an international satellite-based search and rescue distress alert detection system.
The Galileo performances are different for each service. For the Galileo Open Service (OS) no specific requirements of integrity are applicable. The expected performances, once Galileo system is fully deployed, for horizontal positioning accuracy at 95% for a dual-frequency receiver are 4 m (8 m for vertical accuracy), with an availability of the service of 99.5% [1].
In the case of the Galileo Public Regulated Service (PRS), the availability of the service should be 99.5% [2].
Galileo Service Level Perfomances
The performances requirements for each service are the following:
Galileo Open Service Performances
The expected performance once full deployment of the Galileo system at FOC are[1]:
| Galileo Open Service (positioning & timing) | ||
|---|---|---|
| Single Frequency (SF) | Dual Frequency (DF) | |
| Coverage | Global | |
| Accuracy (95%) | Horizontal: 15 m | Horizontal: 4m |
| Vertical: 35 m | Vertical: 8m | |
| Availability | 99.5 % | |
| Timing Accuracy wrt UTC/TAI | 30 ns | |
| Ionospheric Correction | Based on SF Model | Based on DF Measurements |
| Integrity | No | |
Galileo declared its Initial Services status in December 2016 as the first step towards full operational capability. Galileo system deployment will continue with additional satellite launches to enlarge the constellation until it is completed, reaching the Full Operational Capability (FOC) of the Galileo system.
Galileo OS SDD defined a series of Minimum Performance Levels to be achieved until FOC is reached [1]:
| Galileo Open Service Initial Services | ||
|---|---|---|
| SIS Ranging | Accuracy (95%) | 2m |
| Availability | 87% | |
| Timing | UTC Time Dissemination Accuracy(95%) | 30 ns |
| UTC Frequency Dissemination Accuracy (95%) | 3E-13 | |
| GGTO Determination Accuracy (95%) | 20 ns | |
| UTC Availability | 87% | |
| GGTO Availability | 80% | |
Galileo Performance Reports against these MPL values are published in GSC website [3].
Galileo High Accuracy Service
The Galileo High Accuracy Service complements the OS by providing an additional navigation signal and added-value services in a different frequency band. The HAS signal can be encrypted in order to control the access to the Galileo HAS services. Receiver positioning accuracy is foreseen to be at decimetre level.
The Galileo HAS comprises two services levels[4]:
- Service Level 1 (SL1) with global coverage; providing high accuracy corrections (orbits, clocks) and biases (code and phase) for Galileo E1/E5b/E5a/E6 and E5AltBOC and GPS L1/L5/L2 signals.
- Service Level 2 (SL2): with regional coverage; providing SL1 corrections plus atmospheric (at least ionospheric) corrections and potential additional biases.
Next table summarizes the performances for each of the Galileo HAS Service levels:
| PARAMETER | Service Level 1 | Service Level 2 |
|---|---|---|
| Coverage | Global | European Coverage Area (ECA) |
| Horizontal Accuracy 95% | < 20cm | < 20 cm |
| Vertical Accuracy 95% | < 40cm | < 40 cm |
| Convergence Time | < 300 s | < 100 s |
| Availability | 99% | 99% |
Galileo Public Regulated Service Performances
The expected performances of the Galileo PRS service are[2]:
| Galileo Public Regulated Service (PRS) | |
|---|---|
| Dual Frequency (DF) | |
| Accuracy (95%) | Horizontal: 6.5 m |
| Vertical: 12 m | |
| Availability | 99.5 % |
| Timing Accuracy wrt UTC/TAI | 30 ns |
| Ionospheric Correction | Based on DF Measurements |
Galileo Search and Recue Service Performances
Galileo SAR performance values are expressed in terms of Minimum Performance Levels (MPL) for a set of parameters as indicated below[5]:
| Parameter | Expected value | |
|---|---|---|
| Service Availability | Forward Link Service Availability | > 99% |
| European MEOLUT Facility availability in Nominal mode | > 95% | |
| European MEOLUT Facility availability in Degraded mode | > 97.5% | |
| Detection performance | Detection probability after 1 transmitted burst | > 99% |
| Location performance | Location Probability after 1 transmitted burst | > 90% |
| Location Probability after 12 transmitted bursts | > 98% | |
| Location Probability after 1 transmitted burst within 5 km | > 90% | |
| Location Probability after 12 transmitted bursts within 5 km | > 95% | |
| Location Probability after 12 transmitted bursts within 2 km | > 90% |
| Parameter | Expected value |
|---|---|
| Return Link Service Availability | > 95% |
| End-to-end Return Link Service Availability | > 90% |
| Galileo System Message Delivery Latency within 15 minutes | > 99% |
| Return Link Message Reception Probability | > 99% |
| End-to-end Message Delivery Loop Latency within 30 minutes | > 95% |
| Parameter | Expected value |
|---|---|
| SAR Repeater Availability | > 95% |
Combined services performances
Galileo is designed to be interoperable with other systems and, therefore, it will, in a great many instances, be used as part of a combined service. The identification of combined services is necessary to:[2][1]
- Meet the most demanding user applications.
- Reduce satellite navigation system weaknesses.
- Provide robust solutions for applications requiring system redundancy for safety and/or security reasons.
- Access future GNSS market.
- Enable and expand new market opportunities.
The most obvious systems to be combined with Galileo are the other existing GNSS systems, GPS,GLONASS, SBAS and GBAS as they share with Galileo many characteristics that facilitate a combination at user level. By combining Galileo with other GNSS systems, improved performance in the following domains can be expected:
- Availability: Using as an example Galileo in combination with GPS and SBAS systems, the number of operational satellites will be in the region of 60. In normal urban environments this would result in an increased availability for 4 satellites from 40% to more than 90%.
- Position Accuracy: Allied to an increased availability in restricted environments (urban) is a better geometry of spacecraft or enhanced positioning performance.
- Integrity: GNSS based integrity systems and techniques, such as SBAS, ARAIM, RAIM and GBAS, would benefit from the addition of new constellations, including Galileo, in terms of lower achievable protection levels and/or integrity risk.
- Redundancy: By combining services from separate and fully independent systems full redundancy can be achieved. This is particularly important for Safety of Life applications that require full system backup.
Notes
Quarterly Performance Reports are regularly published by the European GNSS Service Centre to provide public information about the measured performance statistics [3] for the available Galileo services.
References
- ^ a b c d Galileo Open Service Service Definition Document
- ^ a b c Galileo Mission High Level Definition, v7.1.
- ^ a b Galileo Performance Reports in GSC website
- ^ a b Galileo High Accuracy Service, Info Note
- ^ Galileo SAR Service Definition Document