EGNOS Training Course

EGNOS Project Office EGNOS Demonstration in CHINA1

EGNOS Training CourseEGNOS Training Course

EGNOS Demonstration in China EGNOS Demonstration in China

O. Perrin, Tianjin, 2 December 2003


ContentsContents

►Short GPS RefresherShort GPS Refresher►What exactly is this EGNOS What exactly is this EGNOS

Project ?Project ?►How does EGNOS work ?How does EGNOS work ?►What is EGNOS transmitting ?What is EGNOS transmitting ?►What is the user computing What is the user computing

with the EGNOS signal ?with the EGNOS signal ?


ContentsContents





GPS BasicsGPS Basics►NAVSTAR GPSNAVSTAR GPS

Navigation Signal Timing and Ranging, Navigation Signal Timing and Ranging, Global Positioning SystemGlobal Positioning System

►USA Satellite Navigation SystemUSA Satellite Navigation System►Developed in the 60’sDeveloped in the 60’s

Merge of Transit and Timation projectsMerge of Transit and Timation projects

►Military system made available free Military system made available free of charge to the civil user of charge to the civil user communitycommunity


GPS Space SegmentGPS Space Segment►Currently 28 operational satellitesCurrently 28 operational satellites

Block I not available any moreBlock I not available any more Currently block II and IIA satellites onlyCurrently block II and IIA satellites only Currently launched satellites IIR (in the Currently launched satellites IIR (in the

future IIR-M with new L2C and M future IIR-M with new L2C and M codes)codes)

Evolutions: block IIF (L5) and GPS IIIEvolutions: block IIF (L5) and GPS III►Fitted with atomic clocks (Rubidium Fitted with atomic clocks (Rubidium

or Caesium) for stable frequency or Caesium) for stable frequency referencereference


GPS orbitsGPS orbits►Medium Earth Orbits (MEO)Medium Earth Orbits (MEO)►6 orbital planes, inclination 55 6 orbital planes, inclination 55

degreesdegrees►4 operational plus 1 spare per plane4 operational plus 1 spare per plane►Altitude of ~20’200 kmAltitude of ~20’200 km►Orbital period of ~12 hoursOrbital period of ~12 hours►Repetition of orbits in ~24 hours Repetition of orbits in ~24 hours

(23 hours 56 minutes)(23 hours 56 minutes)


GPS Signal StructureGPS Signal Structure

►Carrier frequenciesCarrier frequencies L1 1575.42 MHzL1 1575.42 MHz L2 1227.60 MHzL2 1227.60 MHz

►Ranging codesRanging codes L1: C/A (civil) and P (military)L1: C/A (civil) and P (military) L2: P (military)L2: P (military)

►Right Hand Circularly Polarized Right Hand Circularly Polarized SignalSignal


C/A ranging codeC/A ranging code► Pseudo Random Noise (PRN) to identify Pseudo Random Noise (PRN) to identify

the satellites (CDMA)the satellites (CDMA)► Navigation dataNavigation data

50 bps50 bps Satellite ephemerisSatellite ephemeris Satellite almanacs (whole constellation)Satellite almanacs (whole constellation) Satellite health statusSatellite health status UTC informationUTC information Ionospheric parametersIonospheric parameters Satellite clock correctionSatellite clock correction


GPS Ground SegmentGPS Ground Segment► 1 Master Control Station1 Master Control Station

Located in Colorado Springs, USALocated in Colorado Springs, USA

► 5 Monitoring Stations5 Monitoring Stations Hawaii, Ascension Island, Diego Garcia, Hawaii, Ascension Island, Diego Garcia,

Kwajalein, and Colorado SpringsKwajalein, and Colorado Springs

► However, constant tracking of all However, constant tracking of all satellites is not achievedsatellites is not achieved One of the reasons for lack of integrityOne of the reasons for lack of integrity Need for an augmentation for safety-of-life Need for an augmentation for safety-of-life

usersusers


GPS User Segment GPS User Segment (receivers)(receivers)

► Measure the travel time of the signal and Measure the travel time of the signal and multiply it by the speed of light (one-way multiply it by the speed of light (one-way ranging)ranging)

► Computation of 3D position by Computation of 3D position by triangulationtriangulation

► Rx clock is usually not an atomic clockRx clock is usually not an atomic clock Rx clock offset is an additional unknownRx clock offset is an additional unknown Rx measure pseudo-distancesRx measure pseudo-distances

► 4 satellites are needed to compute a 4 satellites are needed to compute a position (3 coordinates plus receiver clock)position (3 coordinates plus receiver clock)


ContentsContents





EGNOS BackgroundEGNOS Background►European Geostationary Navigation European Geostationary Navigation

Overlay ServiceOverlay Service►Global Navigation Satellite System of Global Navigation Satellite System of

the 1the 1stst generation (GNSS-1) generation (GNSS-1)►Augmentation of the existing GPS Augmentation of the existing GPS

(US) and GLONASS (Russia) (US) and GLONASS (Russia) constellationsconstellations

►Project launched in 1998Project launched in 1998►Service for safety-of-life usersService for safety-of-life users


EGNOS PartnersEGNOS Partners

►European Tripartite GroupEuropean Tripartite Group►European Space Agency ESAEuropean Space Agency ESA

Part of ARTES 9 programPart of ARTES 9 program

►European CommissionEuropean Commission Multimodal users and fundingMultimodal users and funding

►EurocontrolEurocontrol Civil aviation usersCivil aviation users


EGNOS ScheduleEGNOS Schedule

►Critical Design ReviewCritical Design Review January 2002January 2002 EGNOS design frozenEGNOS design frozen

►Operational Readiness ReviewOperational Readiness Review 20042004 Technical validation of EGNOSTechnical validation of EGNOS Start of initial operationsStart of initial operations


And the ESTB ?And the ESTB ?►EGNOS System Test BedEGNOS System Test Bed►Prototype system of EGNOS Prototype system of EGNOS

available since early 2000available since early 2000►Reduced systemReduced system►Allows users to gain experience by Allows users to gain experience by

tests and demonstrationstests and demonstrations►Allows testing of expansion Allows testing of expansion

capabilitycapability►System used for the Chinese testsSystem used for the Chinese tests


ContentsContents





EGNOS ArchitectureEGNOS Architecture


Ground Segment: RIMSGround Segment: RIMS

►Ranging and Integrity Monitoring Ranging and Integrity Monitoring StationsStations

►Channels A and B for redundancyChannels A and B for redundancy►Some stations have a channel CSome stations have a channel C►Equipped with an L1/L2 receiver Equipped with an L1/L2 receiver

and atomic clock for precise timingand atomic clock for precise timing►Track GPS, GLONASS and GEOTrack GPS, GLONASS and GEO►EGNOS: 34, ESTB: 12 (+ 3 China)EGNOS: 34, ESTB: 12 (+ 3 China)


Ground Segment: MCCGround Segment: MCC► Master Control CentresMaster Control Centres► Central Processing Facility (CPF)Central Processing Facility (CPF)

Automatic processing of raw data coming Automatic processing of raw data coming from RIMSfrom RIMS

Independent check of measurements of Independent check of measurements of RIMS A by RIMS BRIMS A by RIMS B

► Central Control Facility (CCF)Central Control Facility (CCF) Monitoring and control of EGNOSMonitoring and control of EGNOS

► EGNOS: 4, ESTB: 1EGNOS: 4, ESTB: 1


What is the CPF computing ?What is the CPF computing ?

► Integrity InformationIntegrity Information For each satellite monitoredFor each satellite monitored

►Differential CorrectionsDifferential Corrections Pseudo-range correctionsPseudo-range corrections Orbit and clock correctionsOrbit and clock corrections

► Ionospheric CorrectionsIonospheric Corrections Single layer ionospheric model for Single layer ionospheric model for

L1L1


Ground Segment: NLESGround Segment: NLES

►Navigation Land Earth StationNavigation Land Earth Station►Transmitting the augmentation Transmitting the augmentation

message to each GEO satellitemessage to each GEO satellite►EGNOS: 6 (2 per GEO), ESTB: 1EGNOS: 6 (2 per GEO), ESTB: 1


Space SegmentSpace Segment

►Existing GPS and GLONASSExisting GPS and GLONASS►3 Geostationary Satellites3 Geostationary Satellites

Inmarsat AOR-E (PRN 120)Inmarsat AOR-E (PRN 120) Inmarsat IOR-W (PRN 126)Inmarsat IOR-W (PRN 126) Artemis (PRN 124)Artemis (PRN 124)

►Broadcasting an augmentation Broadcasting an augmentation signal on GPS frequency L1signal on GPS frequency L1

►EGNOS: 3 GEOs, ESTB: 1 (IOR, 131)EGNOS: 3 GEOs, ESTB: 1 (IOR, 131)


User SegmentUser Segment

►Any user equipped with a GPS Any user equipped with a GPS receiver with firmware able to receiver with firmware able to process SBAS data (EGNOS is process SBAS data (EGNOS is broadcast on L1)broadcast on L1)

►Mainly navigation applicationsMainly navigation applications Civil aviationCivil aviation Road transportsRoad transports MaritimeMaritime RailRail


What is EGNOS providing ?What is EGNOS providing ?

► Improved availabilityImproved availability The GEOs can be used as additional The GEOs can be used as additional

ranging sources (GPS-like)ranging sources (GPS-like)

► Improved accuracyImproved accuracy Thanks to differential correctionsThanks to differential corrections

► Improved integrityImproved integrity Thanks to real-time monitoring (6s Thanks to real-time monitoring (6s

TTA)TTA)

► Improved continuityImproved continuity


ContentsContents





EGNOS/ESTB signalEGNOS/ESTB signal►Specifications in RTCA MOPS DO229Specifications in RTCA MOPS DO229►EGNOS SIS is broadcast on the GPS EGNOS SIS is broadcast on the GPS

L1 (1575.42 MHz)L1 (1575.42 MHz)►GEOs use GPS-like PRN code (ESTB: GEOs use GPS-like PRN code (ESTB:

IOR, PRN 131)IOR, PRN 131)►Data rate 250 bits per secondData rate 250 bits per second

5 times faster than GPS data rate5 times faster than GPS data rate

►Forward Error Correction codeForward Error Correction code


Message StructureMessage Structure

►1 message = 250 bits = 1 second1 message = 250 bits = 1 second►250-bit message structure250-bit message structure

8-bit message preamble (for data 8-bit message preamble (for data acquisition purposes)acquisition purposes)

6-bit message type identifier (0 – 63)6-bit message type identifier (0 – 63) 212-bit message data212-bit message data 24-bit message parity (Cyclic 24-bit message parity (Cyclic

Redundancy Check)Redundancy Check)


Message Type 0Message Type 0►Do not use the GEO for safety Do not use the GEO for safety

applicationsapplications►Transmitted every time there is a Transmitted every time there is a

major problem and the system is major problem and the system is completely unavailablecompletely unavailable

►Transmitted during testing phasesTransmitted during testing phases► In ESTB, MT0 contains In ESTB, MT0 contains

pseudorange corrections (1 MT 2 in pseudorange corrections (1 MT 2 in each MT 0 for bandwidth saving each MT 0 for bandwidth saving reasons)reasons)


Message Type 1Message Type 1

►Mask for assignation of the Mask for assignation of the satellitessatellites GPS (PRN 1-37)GPS (PRN 1-37) GLONASS (PRN 38-61)GLONASS (PRN 38-61) SBAS (PRN 120-138)SBAS (PRN 120-138)

►Application of the corrections to Application of the corrections to the right satellite (maximum 51)the right satellite (maximum 51)


Fast CorrectionsFast Corrections► Correction of the fast changing errors (S/A)Correction of the fast changing errors (S/A)► Pseudorange correction for each satellitePseudorange correction for each satellite► MT 2-5: Fast Corrections for 13 satellitesMT 2-5: Fast Corrections for 13 satellites

Fast correction to be applied to the Fast correction to be applied to the pseudorangepseudorange

Integrity: User Differential Range Error Indicator Integrity: User Differential Range Error Indicator (UDREI) (quality of the pseudorange after the (UDREI) (quality of the pseudorange after the application of corrections)application of corrections)

Referring to UDRE (upper bound on the Referring to UDRE (upper bound on the pseudorange error after application of the fast pseudorange error after application of the fast corrections, with 99.9% probability)corrections, with 99.9% probability)


UDREIUDREI

►Can be transmitted inCan be transmitted in MT 2-5 (normal case)MT 2-5 (normal case) MT 6 (all UDREIs, case of an alarm)MT 6 (all UDREIs, case of an alarm)


Long Term CorrectionsLong Term Corrections► Corrections for slow varying errors Corrections for slow varying errors

(satellite position, satellite clock)(satellite position, satellite clock)► MT 25: Long-term Satellite Error MT 25: Long-term Satellite Error

CorrectionsCorrections Satellite position correction (3 parameters)Satellite position correction (3 parameters) Satellite velocity correction (3 parameters)Satellite velocity correction (3 parameters) Satellite clock correction (2 parameters)Satellite clock correction (2 parameters) If no velocity information 4 satellites If no velocity information 4 satellites

otherwise only 2 satellitesotherwise only 2 satellites► MT 24: Mixed Fast Corrections / Long-MT 24: Mixed Fast Corrections / Long-

term Satellite Error Corrections (not term Satellite Error Corrections (not ESTB)ESTB)


Ionospheric CorrectionsIonospheric Corrections► MT 18: ionospheric maskMT 18: ionospheric mask

Ionospheric Grid Points (IGP) maskIonospheric Grid Points (IGP) mask 1808 IGPs (11 bands) all around the world at 1808 IGPs (11 bands) all around the world at

an altitude of 350 km (pre-defined)an altitude of 350 km (pre-defined)

► MT 26: L1 ionospheric correctionsMT 26: L1 ionospheric corrections Vertical delay estimate for 15 IGPs (imaginary Vertical delay estimate for 15 IGPs (imaginary

satellite exactly above the IGP, 90° elevation)satellite exactly above the IGP, 90° elevation) Integrity: Grid Ionospheric Vertical Error Integrity: Grid Ionospheric Vertical Error

Indicator (GIVEI) (0-15) is also transmittedIndicator (GIVEI) (0-15) is also transmitted Refers to GIVE (0.0084 mRefers to GIVE (0.0084 m2 2 - ”Not Monitored”)- ”Not Monitored”)


IGPs for the worldIGPs for the world


Ionospheric Delay Ionospheric Delay ComputationComputation

► Ionospheric Pierce Point (IPP)Ionospheric Pierce Point (IPP)


Ionospheric Delay Ionospheric Delay ComputationComputation

► Interpolation and slant delay Interpolation and slant delay computationcomputation

0

0.5

1

1.5

2

2.5

3

3.5

0 20 40 60 80

Elevation [°]

Ob

liq

uit

y fa

cto

r [-

]


Degradation parametersDegradation parameters► In case the user misses one or In case the user misses one or

more messagesmore messages►MT 7: Fast Corrections MT 7: Fast Corrections

DegradationDegradation UDRE degradationUDRE degradation How quick the corrections changeHow quick the corrections change

►MT 10: Degradation FactorsMT 10: Degradation Factors 15 parameters to evaluate the 15 parameters to evaluate the

degradation of long-term and degradation of long-term and ionospheric correctionsionospheric corrections


GEO Navigation MessageGEO Navigation Message

►MT 9: GEO Ranging Function MT 9: GEO Ranging Function Parameters (Ephemeris) for 1 Parameters (Ephemeris) for 1 GEOGEO GEO satellite position (X, Y, Z)GEO satellite position (X, Y, Z) GEO satellite velocity (VGEO satellite velocity (VXX, V, VYY, V, VZZ))

GEO satellite acceleration (aGEO satellite acceleration (aXX, a, aYY, a, aZZ))

GEO clock offset aGEO clock offset aGf0Gf0 and drift a and drift aGf1Gf1


GEO Almanacs MessageGEO Almanacs Message

►MT 17: GEO Satellite Almanacs for MT 17: GEO Satellite Almanacs for 3 GEOs3 GEOs PRN code numberPRN code number Health and status (Ranging, Health and status (Ranging,

Corrections, Integrity)Corrections, Integrity) Service provider (WAAS, EGNOS, Service provider (WAAS, EGNOS,

MSAS)MSAS) GEO satellite position (almanac)GEO satellite position (almanac) GEO satellite velocity (almanac)GEO satellite velocity (almanac)


SBAS Network TimeSBAS Network Time

►MT 12: SBAS Network Time / UTC MT 12: SBAS Network Time / UTC Offset ParametersOffset Parameters UTC parameters to relate EGNOS UTC parameters to relate EGNOS

time to UTC time (offset, drift, leap time to UTC time (offset, drift, leap seconds)seconds)

Time information (GPS week Time information (GPS week number, GPS TOW,)number, GPS TOW,)


SBAS Service MessageSBAS Service Message

►MT 27: SBAS Service MessageMT 27: SBAS Service Message 1 to 5 Regions can be defined1 to 5 Regions can be defined Increase UDRE values in selected Increase UDRE values in selected

regions in order to guarantee regions in order to guarantee integrityintegrity

New definition (DO229C) implies a New definition (DO229C) implies a triangular or rectangular shape regiontriangular or rectangular shape region

In China, ESTB uses the DO229A In China, ESTB uses the DO229A definition, which creates a circular definition, which creates a circular regionregion


Clock-ephemeris CovarianceClock-ephemeris Covariance►MT 28: Covariance matrix (10 terms)MT 28: Covariance matrix (10 terms)

Expansion of UDRE as a function of the Expansion of UDRE as a function of the user locationuser location

Provides increased availability inside Provides increased availability inside the service area and increased integrity the service area and increased integrity outsideoutside

MT 27 and MT 28 cannot be used MT 27 and MT 28 cannot be used togethertogether

Optional message not broadcast by Optional message not broadcast by ESTBESTB


Additional MessagesAdditional Messages

►MT 62MT 62 Internal Test MessageInternal Test Message Meaningless contentMeaningless content Not used in ESTBNot used in ESTB

►MT 63MT 63 Null Message TypeNull Message Type Filler message if no other message Filler message if no other message

availableavailable


Tropospheric CorrectionsTropospheric Corrections►Local phenomenonLocal phenomenon►Not sent as part of the EGNOS SISNot sent as part of the EGNOS SIS►Tropospheric Correction depends Tropospheric Correction depends

fromfrom Receiver altitudeReceiver altitude Pressure, temperature, humidityPressure, temperature, humidity Day of yearDay of year LatitudeLatitude

►General model to determine these General model to determine these parametersparameters


ContentsContents





Position ComputationPosition Computation► Satellite selection processSatellite selection process

Choice of satellites with SBAS correctionsChoice of satellites with SBAS corrections If not enough, choice of other satellitesIf not enough, choice of other satellites If no solution is possible with SBAS, If no solution is possible with SBAS,

Pegasus does not compute a solutionPegasus does not compute a solution► Pseudorange smoothingPseudorange smoothing

Smoothing filter using carrier phase Smoothing filter using carrier phase measurements (before corrections)measurements (before corrections)

► Pseudorange correctionPseudorange correction

clocktropoionofastmeascorr RCRCRCRC


Measurement ModelMeasurement Model

►3D distance equation3D distance equation

►4 unknowns4 unknowns User position (XUser position (Xuu, Y, Yuu, Z, Zuu)) Receiver clock offset (Receiver clock offset (T)T)

►The user needs to observe at The user needs to observe at least four satellites (same as GPS)least four satellites (same as GPS)

TcZZYYXX svusvusvu 222 )()()(


Solving the equationsSolving the equations

►Linearisation of the equation Linearisation of the equation systemsystem

►Least Square Adjustment using a Least Square Adjustment using a weight matrixweight matrix

1)sin()sin()cos()cos()cos( iiiiii EAEAEH

xHR

RWHWHHx TT 1


Integrity MechanismIntegrity Mechanism► Integrity is the Integrity is the measure of the trust measure of the trust

that can be placed in the correctness that can be placed in the correctness of the information supplied by the of the information supplied by the systemsystem

► It protects the user against misleading It protects the user against misleading or wrong informationor wrong information

► Integrity has to be assessed by each Integrity has to be assessed by each user, depending on the requirement of user, depending on the requirement of his applicationhis application


Integrity MechanismIntegrity Mechanism► The Protection LevelsThe Protection Levels

Depend on the user and satellites position Depend on the user and satellites position (geometry)(geometry)

Computed by the user receiver based on Computed by the user receiver based on information sent by EGNOS information sent by EGNOS

► Compared to Alert LimitsCompared to Alert Limits Alert Limits are fixed for a particular type Alert Limits are fixed for a particular type

of operationof operation PL < AL PL < AL integrity is assured integrity is assured PL PL AL AL integrity can not be assured integrity can not be assured


Protection LevelsProtection Levels

►Protection LevelsProtection Levels Horizontal and Vertical Protection Horizontal and Vertical Protection

LevelsLevels Bound on position error at the 10Bound on position error at the 10-7-7

levellevel Multiplication of estimated errorsMultiplication of estimated errors

►Computed using the projection Computed using the projection matrixmatrix

v

major

TT

dVPL

HPL

WHWHHS

33.5

0.6

)( 1

HPLHPL

VPLVPL


Reference DocumentsReference Documents

►SBAS SpecificationsSBAS Specifications Radio Technical Commission for Radio Technical Commission for

Aeronautics (RTCA): Minimum Aeronautics (RTCA): Minimum Operational Performance Standards Operational Performance Standards (MOPS): DO229 C(MOPS): DO229 C

►Detailed Implementation of MOPSDetailed Implementation of MOPS Pegasus Technical Note (TN)Pegasus Technical Note (TN) Provided under Provided under

Pegasus/DocumentationPegasus/Documentation

EGNOS Training Course

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