# Presentation: 183548

## The Galileo Ground Mission Segment Performances 

***Francisco Amarillo-Fernandez, Massimo Crisci, Alexandre Ballereau***
***John Dow, Martin Hollreiser,  Joerg Hahn, Jean-Luc Gerner, ***
***European Space Agency****** ***

## CONTEXT

-  Presented performance:
- Refer to the Galileo Mission Segment (range domain)
- Are the result of the Segment Critical Design Review (CDR) experimentation process
- Are derived from an experimental platform hosting replicas of the operational  algorithms for both the Navigation and Integrity Functions
- Are derived in synthetic scenarios based on conservative assumptions
- Are confirmed in real scenarios for the Navigation Function

## Introduction (I). Galileo Ground Mission Segment. Functional Overview 

-  Determines and uplinks the navigation data for each Galileo satellite:
-  Orbit description, via 15 orbital parameters
-  OS on-board clock description, via 3 parameters
-  SoL on-board clock description, via 3 parameters
-  TEC global model input parameters
-  Differential group delay between the two OS pilot signals
-  Differential group delay between the two SoL pilot signals
-  Galileo to GPS time offset
-  SoL Signal-In-Space- Accuracy (SISA)
-  Determines  and uplinks the integrity data for the Galileo constellation:
-  Integrity table including the Signal-In-Space-Monitoring-Accuracy (SISMA)
-  Integrity alarms

## Introduction (II). Definitions

**Signal-in-Space Accuracy (SISA) **
- 	“SISA is a prediction of the minimum standard deviation (1-sigma) of the unbiased Gaussian distribution which overbounds the signal-in-space error (SISE) predictable distribution for all possible user locations within the satellite coverage area”
**Signal-in-Space Monitoring Accuracy (SISMA)**
- 	“SISMA shall be a prediction of the minimum standard deviation (1-sigma) of the unbiased Gaussian distribution which overbounds the error of the estimation of SISE as determined by the integrity monitoring system”

## Part I. Tracking Stations Performance

|  | “Initial Reference” quality expectations | “Current”  quality expectations |
| --- | --- | --- |
| Code tracking error
 (excluding multipath) | E5a-Q : Between  6 and 23 cm  
E5b-Q : Between  6 and 23 cm 
E1-C   : Between  15 and 41 cm

Assumptions:
1- Minimum satellite EIRP
2- No ionospheric scintillation  
3- Maximum in band interference
4- Error dependency on satellite elevation (from 5o to 90o)
5- Tracking on pilot
6- Root mean square value | E5a-Q : Between  9 and 31 cm 
E5b-Q : Between 9 and 31 cm  
E1-C   : Between 13 and 41 cm 
 |
| Carrier tracking error 
(excluding multipath) | < 2.5 mm

Assumptions as indicated for the code tracking error (excluding multipath) | Between 2 and 4 mm 
 |
| Code tracking error due to multipath | Between 10 and 100 cm

Assumptions:
1- Worst multipath delay
2- Average multipath phase
3- Range obeys to error dependency versus the D/U ratio. 
4- Applicable to the following signals E5a-Q, E5b-Q, E1-C
5- Tracking on pilot
6- Root mean square value | Between 15 and 140 cm
 |
| Carrier tracking error due to multipath | Between 0.7 and 10 mm

Assumptions as indicated for the code tracking error (due to multipath) | Between 0.8 and 11 mm
 |

## Part II. Orbit & Clock Determination Performance

|  |  “Initial Reference” quality expectations | “Current”  quality expectations |
| --- | --- | --- |
| Predicted 
Clock  and Orbit
UERE | < 130 cm 

Assumptions:
1- 95% percentile
2- End of navigation message applicability period (100 minutes)
3- Worst satellite
4- Worst user location (infinity velocity approach)
5- Masking angle 0o
6- Worldwide network 40 stations | Not in eclipse  < 70 cm 
In eclipse < 78 cm |
| Predicted 
Clock  and Orbit
First derivative of  the
UERE | < 10 mm/s

Assumptions: as above | Not in eclipse < 4.1 mm/s
In eclipse < 4.3 mm/s |
|  Restituted Orbit Error | < 10 cm 
Assumptions: 
1- 67% percentile
2- Worst satellite
3- Average over the arc duration
4- Worldwide network 40 stations | < 12 cm
 |
| Restituted Clock Error | < 0.3 ns

Assumptions: 
1- 67% percentile
2- Worst satellite
3- Average over the arc duration
4- Worldwide network 40 stations | < 0.5 ns
 |

## Part II (continuation-I) 

**Part II (continuation-I) **

**Ranging accuracy (95%) versus satellite and experimentation batch**

**DAY**

## Part III. GTTO Offset Determination Performance

|  |  “Initial Reference” quality expectations |  “Current”  quality expectations |
| --- | --- | --- |
| SoL SISA 
Upper bound | < 85 cm

Assumptions:

1- 68% percentile (by definition)
2- Any time within navigation message applicability period (100 min)
2- Under-bounding probability: 1E-04
3- Upper-bound unavailability probability of: 1E-05
4-  Worst  satellite
5- Galileo over-bounding
6- Signal-In-Space in fault free
7- After convergence
8- Worldwide network: 40 stations | Not in eclipse  < 46 cm
In eclipse < 54 * cm

 * Note: currently under detailed assessment for eclipse condition |

**Part II (continuation-III) **

|  |  “Initial Reference” quality expectations |  “Current”  quality expectations |
| --- | --- | --- |
| Galileo to GPS Time Offset | < 5 ns

Assumptions:

1- 95% percentile
2- Average error over 24 hours
 | < 10.4 ns |

## Part IV. Group Delay Determination Performance

|  | “Initial Reference” quality expectations | “Current”  experimentation results |
| --- | --- | --- |
| Broadcast
Group Delay | Error < 50 cm for L1-C/E5a-Q (OS)

Error < 50 cm for L1-C/E5b-Q (SoL)

Assumptions:

1- 95% percentile
2- Sun Spot Number: 150
3- Average error over a prediction time of 24 hours
4- Worldwide network: DOC 4 | Error < 37 cm for L1-C/E5a-Q

Error < 37 cm for L1-C/E5b-Q
 |

## Part V. Integrity Determination Performance

|  | “Initial Reference” quality expectations | “Current”  experimentation results |
| --- | --- | --- |
| SoL SISMA for Nominal SoL GSS Network | Broadcast SISMA < 70 cm

Assumptions:

1- 68% percentile (by definition)
2- Any time within integrity table applicability period 
3- Under-bounding probability better than 1E-09
4- Unavailability probability better than 1E-05
5-  Worst satellite footprint
6- Sun Spot Number: 250
7- Scintillation modeled
8- Nominal network probability ~ 0.95 
 | No scintillation: <70 cm 
Very strong scintillation: <106 cm

“Current” experimentation results are in line with the “Initial Reference” quality expectations. Nevertheless it is possible to have a sub-set of satellites with degraded monitoring under strong scintillation conditions
 |
| SoL SISMA for Degraded SoL GSS Network
 | Broadcast SISMA < 130 cm

Assumptions as above except:
1- Degraded network probability ~ 0.9995  | No scintillation: <100 cm 
Very strong scintillation: <154 cm

(Comment as above)
 |
| SoL SISA Common Undetected Failure | 2.0E-8 in 150s | 1.9E-8 in 150s
 |

## Part V. (continuation-II) 

**Real-Time Monitoring accuracy (68%) vs satellite footprint. Degraded**

## Part VI. Conclusions

**Exhaustive performance analysis have been carried out on all the Ground Mission Segment (GMS) key performance figures**
**The GMS key algorithms typical performance expectations surpass generally the initial performance expectations**
**At this stage it is considered likely that the performance of the GMS Navigation Determination/Integrity Determination Functions will be overall compatible with the system availability needs**
**The GMS Navigation Determination Function & especially the GMS Integrity Determination Function algorithms will provide level of performance which had never been achieved before by any existing core GNSS System**

## Part VII. Additional Considerations

**Improvements, which are not required to satisfy the System requirements, are possible. ESA is already working hard on the preparation of the technology for “Galileo+” .**
**Nevertheless the performances evaluation cannot be entirely conclusive at this stage, besides the fact of the enormous sophistication of the evaluation process, due to limitations on a number of key physical and engineering models.  Re-evaluation is required and of course planned at IOV **

## THANK YOU