mitre-continuity of navigation using gps and sbas v3

8/2/2019 MITRE-Continuity of Navigation Using GPS and SBAS v3

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2006 The MITRE Corporation. All rights reserved.

Continuity of Navigation usingGPS and SBAS

Presentation for GIT/9Daniel OLaughlin

Dr. S.V. Massimini

April 2006


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2006 The MITRE Corporation. All rights reserved.2

Continuity and Availability

The ARNFS gave extensive results on the availabilityofvarious navigation services in the Asia-Pacific Region

GPS

SBAS

GBAS

GRAS

The ARNFS did not include information on the continuityof navigation operations

Limited capability to model continuity until recently

Objective of this briefing is to familiarize the GIT onaspects of continuity of navigation

Will use recently completed results from Alaska, USA

Later efforts may include results for Asia Pacific


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What are Continuity of Service and

Availability of Service?

Continuityof service is the probability that service will stay

up over a given time span (given that it was up at thebeginning)

Often given as 1 continuity (probability that theservice will fail over a given time span)

Availabilityis the probability that the service is up ifsampled at a random time ( = ratio of up time to total time)

Impact of navigation service unavailability varies withapplication

Time period


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More Continuity Definitions

Continuity Risk = (1 Continuity)

Average Continuity Risk = the Continuity Risk at a user location

averaged over 24 hours

Two types of continuity risk are computed:

PredictedContinuity Risk: Continuity risk associated withpredicted outages (i.e., those known beforehand) e.g., planned

satellite outages for maintenance, geometric outages, etc. For GPS receivers, predicted continuity risk can be avoided if RAIM

predictionsare used in flight planning (with NOTAM updates)

For WAAS receivers, predicted continuity risk can be avoided bychecking WAAS NOTAMs

UnpredictedContinuity Risk: Continuity risk associated withunpredicted outages e.g., satellite or ground equipment failures

Only en routecontinuity risk is computed for this presentation

Horizontal Alert Limit = 2 nmi

Terminal, NPA, and LPV continuity risk can be computed


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ICAO Continuity Requirements

(Annex 10 Table 3.7.2.4-1)


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Assumed Receiver Types

GPS Only (e.g., TSO C129/129A and STC-based)

With and without Baro Aiding

With baro aiding, the standard deviation of pressure altitudeerror was assumed to be 290 m, consistent with aircraft at10,000 ft geometric altitude (see TSO C-129A)

Avionics that assume

SA is on

SA is off

Avionics capable of

Fault Detection (FD) only,

Fault Detection and Exclusion (FDE)

2 and 7.5 degree user mask angle GPS with SBAS (WAAS) (e.g., TSO C145A/146A-based)

With the current WAAS architecture

With the Full LPV Performance WAAS architecture (~2008)


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Modeling Assumptions

These results are from computer models, and aredependent upon a number of assumptions

Changes in assumptions can produce different results

Changes in location can produce different results

Asia-Pacific results could be different than Alaska But do not anticipate major differences

These results do not include any effects of alternative

navigation or inertial navigation systems


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Assumed User Locations

6

5

4

3

2

1

User

-13557.5

-14560

-16060

-152.565

-14570

-16070

LongLat21

4

3

6

5


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Summary of Results:

GPS-Only Avionics, 2Mask Angle

Results Shown are for the24 GPS Martinez Constellation (Appendix B of RTCA DO-229C)

with GPS IFOR Threshold Parameters(values shown are for the worst of the 6 user locations in AK)

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

AveragePredictedContinuity

Risk per hour

AverageUnpredictedContinuity

Risk per hourAvailabilityBaro-AidingFD/FDE

AvionicsAssumption

on SA(On/Off)Case

Baro

No-Baro

Baro

No-Baro

Baro

No-Baro

Baro

No-Baro

1.7404E-038.4165E-079.9985E-01FDEOff8

5.3723E-032.6370E-069.9958E-01FDEOff7

1.7404E-031.1474E-049.9985E-01FDOff6

5.3723E-031.1631E-049.9958E-01FDOff5

2.6671E-031.1455E-069.9978E-01FDEOn4

9.1607E-034.1592E-069.9914E-01FDEOn3

2.6671E-031.1501E-049.9978E-01FDOn2

9.1607E-031.1765E-049.9914E-01FDOn1

Pass =>

Pass =>

Pass =>Pass =>


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Summary of Results:

GPS-Only Avionics , 2Mask Angle

Results Shown are for the Current (Nov 2005) Constellation withNo Failures

(values shown are for the worst of the 6 user locations in AK)

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5


Risk per hour



AvionicsAssumption

on SA(On/Off)Case

8.5726E-064.8780E-061.0000E+00BaroFDEOff16

8.0248E-021.4629E-059.9306E-01No-BaroFDEOff15

8.5726E-061.1828E-041.0000E+00BaroFDOff14

8.0248E-021.2684E-049.9306E-01No-BaroFDOff13

1.4286E-058.1294E-061.0000E+00BaroFDEOn12

8.0246E-021.3014E-059.8264E-01No-BaroFDEOn11

1.4286E-051.2114E-041.0000E+00BaroFDOn10

8.0246E-021.2542E-049.8264E-01No-BaroFDOn9

Pass =>Pass =>

Pass =>Pass =>


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Summary of Results:

GPS-Only Avionics , 7.5Mask Angle< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

Results Shown are for the24 GPS Martinez Constellation (Appendix B of RTCA DO-229C)

with GPS IFOR Threshold Parameters(values shown are for the worst of the 6 user locations in AK)


Risk per hour



AvionicsAssumption

on SA(On/Off)Case

Baro

No-Baro

Baro

No-Baro

Baro

No-Baro

Baro

No-Baro

1.3339E-021.3053E-059.9765E-01FDEOff8

6.3118E-023.4805E-059.9434E-01FDEOff7

1.3339E-021.2546E-049.9765E-01FDOff6

6.3118E-021.4455E-049.9434E-01FDOff5

4.9706E-021.7337E-059.9684E-01FDEOn4

7.3740E-024.1132E-059.8742E-01FDEOn3

4.9706E-021.2922E-049.9684E-01FDOn2

7.3740E-021.5010E-049.8742E-01FDOn1

Pass =>Pass =>

Pass =>Pass =>


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Summary of Results:

GPS-Only Avionics , 7.5Mask Angle

Results Shown are for the Current (Nov 2005) Constellation withNo Failures

(values shown are for the worst of the 6 user locations in AK)

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5


Risk per hour



AvionicsAssumption

on SA(On/Off)Case

Baro

No-Baro

Baro

No-Baro

Baro

No-Baro

Baro

No-Baro

4.1255E-021.3509E-059.9306E-01FDEOff8

1.1875E-014.6642E-059.7917E-01FDEOff7

4.1255E-021.2586E-049.9306E-01FDOff6

1.1875E-011.5494E-049.7917E-01FDOff5

4.1269E-022.1692E-059.9306E-01FDEOn4

1.5407E-015.3607E-059.6181E-01FDEOn3

4.1269E-021.3304E-049.9306E-01FDOn2

1.5407E-011.6105E-049.6181E-01FDOn1

Pass =>Pass =>

Pass =>Pass =>


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Summary of Results:

WAAS Avionics< 10-1

< 10-2

< 10-3

< 10-4

< 10-5

< 10-1

< 10-2

< 10-3

< 10-4

< 10-5


Risk per hour


Risk per hourAvailabilityGPS

ConstellationWAAS

ArchitectureCase

1.7573E-039.5395E-069.9985E-0128 CurrentFLP4

7.0105E-033.7977E-059.9942E-0128 CurrentCurrent3

5.1555E-047.7215E-069.9993E-0124 MartinezFLP2

3.1815E-035.1937E-059.9914E-0124 MartinezCurrent1Pass =>

Pass =>

Pass =>

Pass =>


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Observations (1 of 2)

Predicted continuity risk

With a Pre-flight check (GPS-only avionics) or checkingWAAS NOTAMs (WAAS avionics)

User would be subjected to only predictedcontinuity losses

Without a Pre-flight check (GPS avionics) or check of WAASNOTAMs

User would be subjected to predicted and unpredictedlosses

GPS-only avionics generally have higher rates of predictedcontinuity risk (~10-1 - 10-2 per hour) than WAAS avionics(~10-3 - 10-4 per hour)


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Observations (2 of 2)

Unpredicted continuity risk

For GPS-only avionics, unpredicted continuity risk is lowerfor avionics that perform FDE (~10-5 per hour) than thosethat do not (>~10-4 per hour)

For WAAS avionics, unpredicted continuity loss is ~10-5 to~10-6 per hour


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Conclusions

GPS avionics without FDE do not meetICAO en-routecontinuity requirements

Note that GPS with other navigation aids may be OK

This is why GPS alone is considered supplemental

GPS avionics with FDE meetICAO en-route continuityrequirements

Pre-flight RAIM check must be accomplished

May not be able to depart if RAIM check is not satisfactory

US currently authorizes GPS with FDE as primary meansnavigation in remote areas (with preflight RAIM check)

WAAS avionics meetICAO en-route continuityrequirements

WAAS NOTAMs must be checked

US currently authorizes WAAS as primary means navigation

(with preflight NOTAM check)

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