IGS Workshop 2008

The Galileo Ground Mission Segment Performances

Francisco Amarillo-Fernandez, Massimo Crisci, Alexandre BallereauFrancisco Amarillo-Fernandez, Massimo Crisci, Alexandre BallereauJohn Dow, Martin Hollreiser, Joerg Hahn, Jean-Luc Gerner, John Dow, Martin Hollreiser, Joerg Hahn, Jean-Luc Gerner,

European Space AgencyEuropean Space Agency

IGS Workshop 2008

CONTEXTCONTEXT

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

IGS Workshop 2008

Introduction (I). Introduction (I). Galileo Ground Mission Galileo Ground Mission Segment. Functional OverviewSegment. 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

IGS Workshop 2008

Introduction (II). Introduction (II). DefinitionsDefinitions

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”

IGS Workshop 2008

Part I. Tracking Stations Part I. Tracking Stations PerformancePerformance

“Initial Reference” quality expectations“Current” quality

expectations

Code tracking error (excluding multipath)

E5a-Q : Between 6 and 23 cm Between 6 and 23 cm E5b-Q : Between 6 and 23 cm Between 6 and 23 cm E1-C : Between 15 and 41 cmBetween 15 and 41 cm

Assumptions:1- Minimum satellite EIRP2- No ionospheric scintillation 3- Maximum in band interference4- Error dependency on satellite elevation (from 5º to 90º)5- Tracking on pilot6- Root mean square value

E5a-Q : Between 9 and 31 cm Between 9 and 31 cm E5b-Q : Between 9 and 31 cm Between 9 and 31 cm E1-C : Between 13 and 41 cm Between 13 and 41 cm

Carrier tracking error (excluding multipath)

< 2.5 mm< 2.5 mm

Assumptions as indicated for the code tracking error (excluding multipath)

Between 2 and 4 mm Between 2 and 4 mm

Code tracking error due to multipath

Between 10 and 100 cmBetween 10 and 100 cm

Assumptions:1- Worst multipath delay2- Average multipath phase3- Range obeys to error dependency versus the D/U ratio. 4- Applicable to the following signals E5a-Q, E5b-Q, E1-C5- Tracking on pilot6- Root mean square value

Between 15 and 140 cmBetween 15 and 140 cm

Carrier tracking error due to multipath

Between 0.7 and 10 mmBetween 0.7 and 10 mm

Assumptions as indicated for the code tracking error (due to multipath)

Between 0.8 and 11 mmBetween 0.8 and 11 mm

IGS Workshop 2008

Part II. Orbit & Clock Determination Part II. Orbit & Clock Determination PerformancePerformance

“Initial Reference” quality expectations“Current” quality

expectations

Predicted Clock and Orbit

UERE

< 130 cm < 130 cm

Assumptions:1- 95% percentile2- End of navigation message applicability period (100 minutes)3- Worst satellite4- Worst user location (infinity velocity approach)5- Masking angle 0º6- Worldwide network 40 stations

Not in eclipse < 70 cm < 70 cm In eclipse < 78 cm< 78 cm

Predicted Clock and Orbit

First derivative of the

UERE

< 10 mm/s< 10 mm/s

Assumptions: as above

Not in eclipse < 4.1 mm/s< 4.1 mm/sIn eclipse < 4.3 mm/s< 4.3 mm/s

Restituted Orbit Error

< 10 cm < 10 cm

Assumptions: 1- 67% percentile2- Worst satellite3- Average over the arc duration4- Worldwide network 40 stations

< 12 cm< 12 cm

Restituted Clock Error

< 0.3 ns< 0.3 ns

Assumptions: 1- 67% percentile2- Worst satellite3- Average over the arc duration4- Worldwide network 40 stations

< 0.5 ns< 0.5 ns

IGS Workshop 2008

Part II (continuation-I) Part II (continuation-I) Ranging accuracy (95%) versus satellite and experimentation batch

DAY

IGS Workshop 2008

Part III. GTTO Offset Determination PerformancePart III. GTTO Offset Determination Performance

“Initial Reference” quality expectations “Current” quality expectations

SoL SISA Upper bound

< 85 cm< 85 cm

Assumptions:

1- 68% percentile (by definition)2- Any time within navigation message applicability period (100 min)2- Under-bounding probability: 1E-043- Upper-bound unavailability probability of: 1E-054- Worst satellite5- Galileo over-bounding6- Signal-In-Space in fault free7- After convergence8- Worldwide network: 40 stations

Not in eclipse < 46 cm< 46 cmIn eclipse < 54 * cm< 54 * cm

* Note: currently under detailed assessment for eclipse condition

Part II (continuation-III) Part II (continuation-III)

“Initial Reference” quality expectations “Current” quality expectations

Galileo to GPS Time

Offset

< 5 ns< 5 ns

Assumptions:

1- 95% percentile2- Average error over 24 hours

< 10.4 ns

IGS Workshop 2008

Part IV. Group Delay Determination Part IV. Group Delay Determination PerformancePerformance“Initial Reference” quality expectations “Current” experimentation

results

BroadcastGroup Delay

Error < 50 cm< 50 cm for L1-C/E5a-Q (OS)

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

Assumptions:

1- 95% percentile2- Sun Spot Number: 1503- Average error over a prediction time of 24 hours4- Worldwide network: DOC 4

Error < 37 cm< 37 cm for L1-C/E5a-Q

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

IGS Workshop 2008

Part V. Integrity Determination PerformancePart V. Integrity Determination Performance“Initial Reference” quality expectations “Current” experimentation

results

SoL SISMA for Nominal

SoL GSS Network

Broadcast SISMA < 70 cm< 70 cm

Assumptions:

1- 68% percentile (by definition)2- Any time within integrity table applicability period 3- Under-bounding probability better than 1E-094- Unavailability probability better than 1E-055- Worst satellite footprint6- Sun Spot Number: 2507- Scintillation modeled8- Nominal network probability ~ 0.95

No scintillation: <70 cm <70 cm Very strong scintillation: <106 cm<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< 130 cm

Assumptions as above except:1- Degraded network probability ~ 0.9995

No scintillation: <100 cm<100 cm Very strong scintillation: <154 cm<154 cm

(Comment as above)(Comment as above)

SoL SISA Common

Undetected Failure

2.0E-8 in 150s 1.9E-8 in 150s

IGS Workshop 2008

Part V. (continuation-II) Part V. (continuation-II) Real-Time Monitoring accuracy (68%) vs satellite footprint. Degraded

IGS Workshop 2008

Part VI. ConclusionsPart 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

IGS Workshop 2008

Part VII. Additional ConsiderationsPart 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

IGS Workshop 2008

THANK YOUTHANK YOU

Email: Email: Francisco.Amarillo.Fernandez@esa.intTelephone: +31 71 565 3446Telephone: +31 71 565 3446