Satellite Positioning and Satellite Positioning and

Navigation SystemsNavigation Systems

Prof. Wu ChenProf. Wu ChenDepartment of Land Surveying and Department of Land Surveying and

GeoinformaticsGeoinformaticsHong Kong Polytechnic UniversityHong Kong Polytechnic UniversityEmail: Email: lswuchen@polyu.edu.hklswuchen@polyu.edu.hk

Tel: 27665969Tel: 27665969

Where and When?Where and When?

Timing AccuracyTiming Accuracy

TypeType ms/dayms/day Time to Time to Lose one SecLose one Sec

HydrogenHydrogen 1010-5-5-10-10-7-7 30,000,000 yr30,000,000 yr

Cesium & rubidiumCesium & rubidium 1010-4-4-10-10-5-5 300,000 yr300,000 yr

Quartz crystalQuartz crystal 1-101-10-4-4 30 yr30 yr

Earth rotationEarth rotation 10 -110 -1

PendulumPendulum 10 - 10010 - 100

Positioning Accuracy – Positioning Accuracy – Global Global

• Space-based Space-based – i.e. GNSSi.e. GNSS– Accuracy: Accuracy: 1 cm (surveying) 1 cm (surveying)

1 m -10 m 1 m -10 m (Nav)(Nav)

• Ground-basedGround-based– i.e. Loran-Ci.e. Loran-C– Accuracy: Accuracy: 200 m200 m

• Celestial Celestial – i.e. Starsi.e. Stars– Accuracy: Accuracy: a few nmia few nmi

Precise Timing is crucial for Precise Timing is crucial for PositioningPositioning• John Harrison John Harrison

Chronometer (1764)Chronometer (1764)– James Cook’s global James Cook’s global

voyage voyage

• Atomic ClockAtomic Clock– To make GPS possibleTo make GPS possible

• Next Gen. ClockNext Gen. Clock– Cold Atom (2001 Noble Cold Atom (2001 Noble

Price)Price)– 3-4 order better than 3-4 order better than

conventional Atomic conventional Atomic ClockClock

Positioning Technologies – Positioning Technologies – Power of nationsPower of nations

• Development of Marine NavigationDevelopment of Marine Navigation– Emerged “Ocean Power Countries”Emerged “Ocean Power Countries”

• Development of Modern Positioning Development of Modern Positioning TechnologiesTechnologies– GPS, Satellite Remote Sensing, INS, etcGPS, Satellite Remote Sensing, INS, etc– Military Dominance of USAMilitary Dominance of USA– Recent Wars (i.e. Iraqi wars)Recent Wars (i.e. Iraqi wars)

Positioning MethodsPositioning Methods

• Land MarkingLand Marking

• Celestial PositioningCelestial Positioning

• Distance and anglesDistance and angles

Land MarkingLand Marking

• Visual Visual – Nature land shapesNature land shapes– BuildingsBuildings– ImagesImages– Lighthouse, “Aobao”Lighthouse, “Aobao”

• Non-visualNon-visual– BeaconsBeacons– Terrain MatchingTerrain Matching– Signal Matching (“Finger print”)Signal Matching (“Finger print”)

Celestial PositioningCelestial Positioning

• Reference to StarsReference to Stars

• DirectionDirection– ““Star of North”Star of North”

• LatitudeLatitude– Angle of star locationAngle of star location

• LongitudeLongitude– Time Time when when stars passing youstars passing you

DirectionDirection• ‘‘North’ North’

– True North: rotation axis of the earthTrue North: rotation axis of the earth– Magnetic North: ‘north’ end of magnetic needle, Magnetic North: ‘north’ end of magnetic needle,

affected by the earth’s magnetic field only.affected by the earth’s magnetic field only.– Grid North: ‘north’ of a map, dependent on map Grid North: ‘north’ of a map, dependent on map

projectionprojection– Bearing:Bearing:

•Horizontal angle referenced to the ‘north’Horizontal angle referenced to the ‘north’

• Measurement of NorthMeasurement of North– CompassCompass– GyroGyro– Two known pointsTwo known points

Distance MeasurementDistance Measurement

One-way ranging (GPS, GLONASS)

Measure t = / c = one-way time of travelCalculate = c t Two unsynchronised clocks

Measure t = 2 / c = two-way time of travel

Calculate = c t / 2One clock used to measure t

Two-way ranging(PRARE)

DOPPLER EFFECTDOPPLER EFFECT

Frequency

Time

Position Fixing GeometryPosition Fixing Geometry

• MeasurementsMeasurements– DirectionDirection– distancedistance– Distance differenceDistance difference– Distance rateDistance rate

• QuestionQuestion: What does a single : What does a single measurement tell us about our Position?measurement tell us about our Position?

• Surface of Position (SOP, 3D)Surface of Position (SOP, 3D)• Line of Positioning (LOP, 2D)Line of Positioning (LOP, 2D)

DistanceDistance

• SOP (LOP)SOP (LOP)– Sphere (Circle)Sphere (Circle)

• Positioning FixPositioning Fix

Distance differenceDistance difference

• SOP (LOP)SOP (LOP)– HyperbolicHyperbolic

• Positioning FixPositioning Fix

Distance rateDistance rate• SOP (LOP)SOP (LOP)

– HyperbolicHyperbolic

• Positioning fixPositioning fix

Intersection of two hyperboloids with Earth sphere

NN1212

NN2323tt11

tt22

tt33BB

Doppler Shift

frequency++

f + Doppler

f - Doppler

ff

DirectionDirection

• SOP (LOP)SOP (LOP)– Plane (Line)Plane (Line)

• Positioning fixPositioning fix– Intersection or resectionIntersection or resection

P

A

B

C AB

C

P

Mix modeMix mode

• Any two LOPs or three SOPs which have intersection can be Any two LOPs or three SOPs which have intersection can be used for position fixused for position fix

• Lop AmbiguitiesLop Ambiguities– Good approximation of initial positionGood approximation of initial position– Extra LOPExtra LOP

• Many combinationsMany combinations– Range-directionRange-direction– Two rangesTwo ranges– Two directionsTwo directions– Range-range differenceRange-range difference– Two range differencesTwo range differences– Two anglesTwo angles– ……………………………………..

Geometry of PositioningGeometry of Positioning

Bad Geometry Good Geometry

Pseudorange Error R2

Pseudorange Error R1

R1 R2R1 R2

DOP

Modern Positioning SystemsModern Positioning Systems• Gyro Compass (magnetic compass)Gyro Compass (magnetic compass)• Inertial navigation systems (INS)Inertial navigation systems (INS)• RadarRadar• Terrestrial radio navigation systemsTerrestrial radio navigation systems• Satellite navigation systemsSatellite navigation systems• Charts and mapsCharts and maps• Sonar systemsSonar systems• Doppler SystemsDoppler Systems• ImagesImages• MobilephoneMobilephone• Wireless Sensor networksWireless Sensor networks• ……………………..

Professions related to Professions related to PositioningPositioning

• SurveyingSurveying– Shape of Earth, Shape of Earth, – Reference systemsReference systems– MapsMaps– DeformationDeformation– Engineering surveyingEngineering surveying

• NavigationNavigation– From person to spaceshipFrom person to spaceship– AnimalsAnimals

• Guidance and PointingGuidance and Pointing– Military Military – EngineeringEngineering

Navigation QuestionsNavigation Questions

• Can I get there from here?Can I get there from here?– If YES, By which routeIf YES, By which route

• How long will it take?How long will it take?

• Where are we now?Where are we now?

• Where else could we go from here?Where else could we go from here?

• What is that thing over there, where is What is that thing over there, where is it?it?– Aids of navigation, maps,.....Aids of navigation, maps,.....

Basic Tasks of NavigationBasic Tasks of Navigation

• PositioningPositioning– KinematicKinematic

• RoutingRouting– Select a way to go to the destinationSelect a way to go to the destination

•SafeSafe

•LegalLegal

•FastFast

•CheapCheap

•ConvenientConvenient

Types of NavigationTypes of Navigation

– SpaceSpace– MarineMarine

• SurfaceSurface

• Under seaUnder sea

• IMO, IALAIMO, IALA

– Air Air • ICAOICAO

– Land: cars, trains, person…Land: cars, trains, person…– RobotsRobots– birdbird

Information required for Information required for NavigationNavigation

• My Position, course, etc.My Position, course, etc.

• Surrounding environmentSurrounding environment– Moving or static objectsMoving or static objects– Radar, maps, sightsRadar, maps, sights

• Nature environmentsNature environments– Weather, currents, tides…Weather, currents, tides…

• Routing toolsRouting tools

Navigation observablesNavigation observables

• Distance and anglesDistance and angles

• Earth’s rotation and astronomyEarth’s rotation and astronomy

• Earth’s propertiesEarth’s properties– Magnetic gravitational, electric, heatMagnetic gravitational, electric, heat– Topographic featuresTopographic features

• Vehicle motionVehicle motion

• Radio signalsRadio signals

Bird migrationBird migration

• Example: Artic Term migrates from Example: Artic Term migrates from Arctic and Antarctic & back (40000 Arctic and Antarctic & back (40000 km /year)km /year)

• Birds useBirds use– Astronomy: sensing positions of sun, moon, Astronomy: sensing positions of sun, moon,

and starsand stars– Landmarks: recognize mountains, rivers, Landmarks: recognize mountains, rivers,

coastlinescoastlines– Sensitivity to magnetic fieldSensitivity to magnetic field

Kinematic positioningKinematic positioning

• To determine the kinematic state of a To determine the kinematic state of a moving objectmoving object– TimeTime– Position (3D) (latitude, longitude, height)Position (3D) (latitude, longitude, height)– Orientation (3D) (roll, pitch heading)Orientation (3D) (roll, pitch heading)– Velocity (6D)Velocity (6D)– Acceleration (6D)Acceleration (6D)

Navigating Process:Navigating Process:

Determine PosCheck VelocityChange Accel.

HomingHoming

• Given a target positionGiven a target position• 1 Determine present position1 Determine present position• 2 Compute position relative to target2 Compute position relative to target• 3 Determine present velocity3 Determine present velocity• 4 Calculate course and speed change 4 Calculate course and speed change

required to reach target on schedulerequired to reach target on schedule• 5 apply course and speed change5 apply course and speed change• 6. return to 16. return to 1

Tracking controlTracking control

• Given a specified trackGiven a specified track– 1. Determine position1. Determine position– 2. compute distance off track2. compute distance off track– 3. determine the course and speed3. determine the course and speed– 4. compute rate of change4. compute rate of change– 5. alter course to come back track5. alter course to come back track– 6. return to 16. return to 1

Required Navigation Required Navigation Performance (RNP)Performance (RNP)

• Different user groupsDifferent user groups– Air, marine, space, land,…Air, marine, space, land,…

• Different stagesDifferent stages– Flight: En route, terminal, precision and non-Flight: En route, terminal, precision and non-

precision approach, landing, surface operationprecision approach, landing, surface operation

• Safety of life operationSafety of life operation

• International and national standardsInternational and national standards– ICAO, IMO, IALA, IHOICAO, IMO, IALA, IHO– National authoritiesNational authorities

Performance IndicatorsPerformance Indicators

• AccuracyAccuracy• AvailabilityAvailability• CapacityCapacity• ContinuityContinuity• CoverageCoverage• DimensionDimension• IntegrityIntegrity• ReliabilityReliability• Update rate (Fix rate)Update rate (Fix rate)• costcost

AccuracyAccuracy

• Accuracy: The degree of conformance Accuracy: The degree of conformance (95%?) between an estimated (95%?) between an estimated parameter of an object at a given time parameter of an object at a given time and the true value of that parameterand the true value of that parameter

• Predictable accuracy (compare to the Predictable accuracy (compare to the true)true)

• Repeatable accuracy (compare to itself)Repeatable accuracy (compare to itself)

• Relative accuracy (compare to others)Relative accuracy (compare to others)

• Availability: percentage of time that the Availability: percentage of time that the system is usable. system is usable.

• Integrity: the ability of a navigation Integrity: the ability of a navigation system to provide timely warnings to the system to provide timely warnings to the users when the system should not be users when the system should not be used.used.

• Reliability is the probability of performing Reliability is the probability of performing a specified function without failure under a specified function without failure under given conditions for a specified period of given conditions for a specified period of timetime

• Continuity: the ability of a system to Continuity: the ability of a system to perform a function without interruption perform a function without interruption during an intended operation. during an intended operation.

• It can be described as the probability that It can be described as the probability that the specified system performance will be the specified system performance will be maintained for the duration of operation, maintained for the duration of operation, assuming that the system was available assuming that the system was available at the beginning of that phase of at the beginning of that phase of operationoperation

RedundancyRedundancy

• Redundancy allows reliability to be Redundancy allows reliability to be monitored (do you think you get the monitored (do you think you get the accuracy you think you get?)accuracy you think you get?)

• How to provide redundancyHow to provide redundancy– Repeat measurementsRepeat measurements– Add more measurementsAdd more measurements

• First rule in navigationFirst rule in navigation– Never dependent upon one systemNever dependent upon one system

IntegrationIntegration

Take advantages of each system toTake advantages of each system to• Improve the performance of navigationImprove the performance of navigation

– IntegrityIntegrity– ContinuityContinuity– AccuracyAccuracy– AvailabilityAvailability– ReliabilityReliability

• Add more functionsAdd more functions– i.e. Navigation + communicationsi.e. Navigation + communications

What need to be considered to What need to be considered to integrate different systems?integrate different systems?

• BenefitsBenefits– PerformancePerformance– FunctionsFunctions– CostCost

• FeasibilityFeasibility– Application drivenApplication driven– CostCost– Other factorsOther factors

• How to integrate different How to integrate different systemssystems– Hardware Hardware – SoftwareSoftware– AlgorithmsAlgorithms– InterfacesInterfaces

Developments in SurveyingDevelopments in Surveying

• ConventionallyConventionally– ‘‘Static’ Surveys (mins)Static’ Surveys (mins)– Discrete PointsDiscrete Points– Two receiversTwo receivers– Post ProcessedPost Processed

• Integrated Survey SystemsIntegrated Survey Systems– Dynamic SurveysDynamic Surveys– Multiple ObservationsMultiple Observations– Integrated SensorsIntegrated Sensors– Real-timeReal-time

Position Information for other Position Information for other usersusers

• Scientific ResearchScientific Research

• EngineeringEngineering

• Environment monitoringEnvironment monitoring

• Emergency ResponseEmergency Response

• Urban PlanningUrban Planning

• GISGIS

Very Long Baseline Interferometry Very Long Baseline Interferometry (VLBI)(VLBI)

• Receive signal from pulse stars (Receive signal from pulse stars (quasars)quasars) (very weak signals)(very weak signals)

• Two stations measure signal delay Two stations measure signal delay differencedifference

• First technique measures distances overFirst technique measures distances over a thousand kilometres with accuracy of mm a thousand kilometres with accuracy of mm

Satellite Laser Ranging Satellite Laser Ranging (SLR)(SLR)

• Transmit Laser pulse to SatelliteTransmit Laser pulse to Satellite

• Satellite Reflects signal back to earthSatellite Reflects signal back to earth

• Measure signal travel time => Measure signal travel time => DistanceDistance

• Orbit and Station Position Orbit and Station Position DeterminationDetermination=>Gravity and Station coordinates=>Gravity and Station coordinates

Satellite AltimetrySatellite Altimetry

• Radar to measure distance Radar to measure distance from Satellite to Earthfrom Satellite to Earth

• Ocean CirculationOcean Circulation• Direct measurement of Direct measurement of

GeoidGeoid

Synthetic Aperture Radar Synthetic Aperture Radar ((SAR)SAR)

• Scan distance to convert to a imageScan distance to convert to a image

• Size of image: 100x100 kmSize of image: 100x100 km

• Not Affected by weatherNot Affected by weather

Synthetic Aperture Radar Synthetic Aperture Radar ((SAR)SAR)• Very Wide ApplicationsVery Wide Applications

– Ocean: environmental, wave, ice, etcOcean: environmental, wave, ice, etc– Land: Land:

• images: Land use monitoring, flood,..images: Land use monitoring, flood,..•penetrate vegetation, geological featurepenetrate vegetation, geological feature•Global DTM modelGlobal DTM model•soil types: moisture, ...soil types: moisture, ...

The Technology Image the ground surface with satellite radar Process data using advanced numerical techniques to detect and measure accurately ground surface change The technology is accurate, economical, efficient and

highly automatic Application areas: - Land settlement measurement

- Landslide monitoring

- Earthquake studies

- DEM generation

- … …

Observed land subsidence of part of reclaimed land in HK

InSAR Technology for Ground Change Detection/MeasurementInSAR Technology for Ground Change Detection/Measurement

Satellite GradiometerSatellite GradiometerGRACE MISSION (NASA)GRACE MISSION (NASA)

High resolution gravity fieldHigh resolution gravity fieldto yield complete gravity vectorto yield complete gravity vectorto model near surface disturbing massto model near surface disturbing massto help delicate geophysical interpretationto help delicate geophysical interpretation

GRACE (2002 -2004 )gravity map

pre-GRACE (~ 40 years)gravity map

GeophysicsGeophysics

• Glacial ReboundGlacial Rebound– Relief of Ice cover - Relief of Ice cover -

• Free Oscillation Free Oscillation – Excited by certain eventsExcited by certain events

• Earth TideEarth Tide– Periodical deformation of the earth Periodical deformation of the earth

caused by the attractions from the Sun caused by the attractions from the Sun and the Moonand the Moon

• Movement of CoreMovement of Core

Plate TectonicsPlate Tectonics

Plate TectonicsPlate TectonicsDivergent boundaries

Continental-continental convergence

Global Tectonic MovementsGlobal Tectonic Movements

Seismic ResearchSeismic Research

• EarthquakesEarthquakes– Movements of faultsMovements of faults– Most of them along the boundaries of Most of them along the boundaries of

tectonic platestectonic plates

• Geodetic methodsGeodetic methods– Measure the movements of pre, in and Measure the movements of pre, in and

post quakespost quakes– To help understanding the earthquakesTo help understanding the earthquakes

Atmosphere ScienceAtmosphere Science

• IonosphereIonosphere– Free charged particles due to solar radiationFree charged particles due to solar radiation– Coupled with geomagnetic fieldCoupled with geomagnetic field– Important for communication, navigation Important for communication, navigation

and remote sensingand remote sensing

• Space technologies (VLBI, GPS)Space technologies (VLBI, GPS)– Determine the electron distribution in spaceDetermine the electron distribution in space

Atmosphere ScienceAtmosphere Science

• Troposphere refraction is the error Troposphere refraction is the error sources in GPS positioningsources in GPS positioning

• On the other hand, if we know the On the other hand, if we know the amount of refraction delay – total amount of refraction delay – total water vapour content along the water vapour content along the signal passsignal pass

• Metrological studies, weather Metrological studies, weather forecastingforecasting

OceanographyOceanography

• In recent years, we understand the In recent years, we understand the ocean environment is an important ocean environment is an important factor to control global climatefactor to control global climate– i.e. El Ninoi.e. El Nino

• Sea surface topographySea surface topography– Ocean circulationOcean circulation– Wave Wave – Mean Sea Level (MSL)Mean Sea Level (MSL)

• GPS buoys, GPS-Tide Gauge connectionGPS buoys, GPS-Tide Gauge connection• Altimetry, SAR……Altimetry, SAR……

European Tide Gauge European Tide Gauge RecordsRecordsEuropean Tide Gauge European Tide Gauge RecordsRecords

1920

500

1000

1500

2000

1860

MS

L (

mm

)

0

1890

1950

1980

StockholmStockholm

CascaisCascais

BrestBrest

NewlynNewlyn

AberdeenAberdeen

Global WarmingGlobal Warming

• It is a fact that the earth It is a fact that the earth temperature is risingtemperature is rising– Disaster situationsDisaster situations– More flood, more draught, Ice More flood, more draught, Ice

ages, ages,

• Monitor the effects:Monitor the effects:– Ice sheetsIce sheets– Sea levelSea level

Space ExplorationSpace Exploration

• Precise OrbitsPrecise Orbits– Gravity and other force modelsGravity and other force models– Tracking technologiesTracking technologies

• Gravity Fields of other planetsGravity Fields of other planets

• Remote SensingRemote Sensing– Image correction and registrationImage correction and registration

Military ApplicationsMilitary Applications

• Precise GravityPrecise Gravity– Precise Orbits for satellites and missiles Precise Orbits for satellites and missiles – Deflection of verticalDeflection of vertical

• Global Reference FrameGlobal Reference Frame– NavigationNavigation

• Global DTM Global DTM – NavigationNavigation– Cruise Missiles, airplanesCruise Missiles, airplanes

• Guided WeaponsGuided Weapons

Water Leakage – Need Water Leakage – Need positionposition

Position Information for Position Information for ordinary peopleordinary people

• Technology is readyTechnology is ready– GPSGPS– Mobile phoneMobile phone– WiFiWiFi– Wireless Sensor networkWireless Sensor network

• Provide seamless positioning Provide seamless positioning anywhere you are, and relevant anywhere you are, and relevant information neededinformation needed

Internet RevolutionInternet Revolution

• InternetInternet– Communication + informationCommunication + information

• Great Impact on human behaviour Great Impact on human behaviour and Economy and Economy

• Create a “Virtue World”Create a “Virtue World”

Return to the real worldReturn to the real world

• Mobile internet + PositionMobile internet + Position

• Information at the location needed, Information at the location needed,

• And real-timeAnd real-time

• Potentially, very wide and profound Potentially, very wide and profound applicationsapplications

• Time + Position + InformationTime + Position + Information=> real-world=> real-world

Introduction of Global Introduction of Global Navigation Satellite Navigation Satellite

Systems (GNSS)Systems (GNSS)

HISTORY OF SATELLITE NAVIGATIONHISTORY OF SATELLITE NAVIGATION- Sputnik I -- Sputnik I -

• 4.10.19574.10.1957 Sputnik I (USSR), first artificial satelliteSputnik I (USSR), first artificial satellite

• 3.11.19573.11.1957 Sputnik II (USSR), dog Laika on-boardSputnik II (USSR), dog Laika on-board

• 1.2.19581.2.1958 Explorer I (USA), discovery of Van-Allan Explorer I (USA), discovery of Van-Allan BeltBelt– Venture of USA/USSR into space had begunVenture of USA/USSR into space had begun– After advent of Sputnik many activities were After advent of Sputnik many activities were

undertaken to determine its orbitundertaken to determine its orbit– John Hopkins Applied Physics Labs (APL) used John Hopkins Applied Physics Labs (APL) used

Doppler shift measurements for orbit Doppler shift measurements for orbit determinationdetermination

AMERICAN TRANSIT SYSTEM (1)AMERICAN TRANSIT SYSTEM (1)

• 1959: Development started1959: Development started

• 1964: Operational for military use1964: Operational for military use

• 1967: Released for civil use1967: Released for civil use

• 1997: Phase-out1997: Phase-out

• Orbital height: 1075 km (LEO)Orbital height: 1075 km (LEO)

• Orbital period: 107 minOrbital period: 107 min

• Polar orbits i Polar orbits i 90° 90°

• Two carrier frequencies: fTwo carrier frequencies: f22 = 400, f = 400, f11 = 150 MHz = 150 MHz

• 2-d navigation system only2-d navigation system only

• Time interval between position fixes: 35 to 100 minTime interval between position fixes: 35 to 100 min

• Accuracy (1 Accuracy (1 ): 200 m (400 m)): 200 m (400 m)

AMERICAN TRANSIT SYSTEM (2)AMERICAN TRANSIT SYSTEM (2)

• Since 1973: 9 OSCAR and 3 NOVA Since 1973: 9 OSCAR and 3 NOVA satellites have been launchedsatellites have been launched

• Mainly designed for ship Mainly designed for ship navigation (Geodetic applications)navigation (Geodetic applications)

• Last launch: 1988Last launch: 1988

+Z axis

Earth

Boom

Discos sensor

Digital SAD

Rotating solar panels (2)(solar cells one side)

Command antenna (2)

Spin SAD

Transmitting antenna(150 ... 400 MHz)

Microthrusters (2)(Tellon Fuel)

Rotate ± 180°

Fixed solar panels (2)(solar cells both sides)

Orbit adjust and transfer system(station seeking rocket)

Momentum wheel

RUSSIAN TSIKADA SYSTEMRUSSIAN TSIKADA SYSTEM

• Russian equivalent to TRANSITRussian equivalent to TRANSIT

• Exists since 1965Exists since 1965– Eight military satellites (TSIKADA-M)Eight military satellites (TSIKADA-M)– Four civil satellitesFour civil satellites

• Orbital period: 105 minOrbital period: 105 min

• Inclination: Inclination: ii = 83° = 83°

• Dual frequency system: Dual frequency system: ff11 = 150 MHz, = 150 MHz, ff22 = 400 MHz = 400 MHz

• Accuracy (1 Accuracy (1 ): 200 m ): 200 m 400 m 400 m

• First Soviet navigation satellite Tsyklon (Kosmos First Soviet navigation satellite Tsyklon (Kosmos 192) launched in LEO 1967 based on Doppler 192) launched in LEO 1967 based on Doppler principleprinciple

• 1970: Program start1970: Program start• Joint program of CNES/NASA/NOAAJoint program of CNES/NASA/NOAA• Two meteorological NOAA satellites (Two meteorological NOAA satellites (hh = 850 km; = 850 km;

ii = 99°) = 99°)• Platforms transmit an Platforms transmit an

identification code at 401.65 MHzidentification code at 401.65 MHz• Doppler receiver at satelliteDoppler receiver at satellite• Doppler data down-linked Doppler data down-linked

to 3 telemetry stationsto 3 telemetry stations• Position determination of platform Position determination of platform

at Argos centre in Toulouseat Argos centre in Toulouse• System capacity: 1000 platformsSystem capacity: 1000 platforms

simultaneously simultaneously • Accuracy: several kmAccuracy: several km

AMERICAN-FRENCH ARGOS SYSTEMAMERICAN-FRENCH ARGOS SYSTEM

Localisation

1

2

3

4

5

DAWN OF THE NEXTDAWN OF THE NEXT GENERATIONGENERATIONNAVIGATION SATELLITE (1972)NAVIGATION SATELLITE (1972)

• Space was being used for many thingsSpace was being used for many things– CommunicationsCommunications– ListeningListening– Looking (up and down)Looking (up and down)– Navigation (Transit, Tsikada)Navigation (Transit, Tsikada)– Science (Measuring)Science (Measuring)

• New space-based navigation systems were New space-based navigation systems were being proposed, but as competitors to each otherbeing proposed, but as competitors to each other– Timation (US Naval Research Laboratory)Timation (US Naval Research Laboratory)– 621B (US Air Force Space and Missile Organization)621B (US Air Force Space and Missile Organization)– Transit (US Navy Special Programs)Transit (US Navy Special Programs)

EXISTING AND PLANNED DOD EXISTING AND PLANNED DOD NAVIGATION SYSTEMS IN 1972NAVIGATION SYSTEMS IN 1972

SystemSystem Sponsor Sponsor OrbitsOrbits SignalsSignals CharacteristicsCharacteristics

TRANSITTRANSIT APL/NavyAPL/Navy Polar, Polar, Tone/Tone/ Periodic, 2D (existing) Periodic, 2D (existing) circular,circular, Low Low Doppler Doppler self-jammingself-jamming

TIMATIONTIMATION NRL/NavyNRL/Navy 8-hr, 8-hr, Side toneSide tone 2D, dynamic2D, dynamic

(experimental)(experimental) circular circular RangingRanging easily easily jammedjammed

InclinedInclined (Rb/Cs clocks)(Rb/Cs clocks)

621B621B SAMSO/AFSAMSO/AF Egg beater,Egg beater, PRNPRN 3D, dynamic3D, dynamic

(planned,(planned, RegionalRegional Spread Spread good A/Jgood A/J

ground tests) ground tests) SpectrumSpectrum

(ground control)(ground control)

THE MAJOR TECHNICAL ISSUESTHE MAJOR TECHNICAL ISSUES

• Control segment vulnerabilityControl segment vulnerability

• User jamming / spoofingUser jamming / spoofing

• User equipment costsUser equipment costs

• Satellite lifetimeSatellite lifetime

• Ionospheric correctionsIonospheric corrections

These problems are also relevant todayThese problems are also relevant today

GPS SYSTEMGPS SYSTEM

SpaceSegment

UserSegment

ControlSegment

ColoradoSprings

HawaiiKwajaleinAscension IslandDiegoGarcia

Monitor Stations

EXPECTED GLOBAL EXPECTED GLOBAL POSITIONING SYSTEM POSITIONING SYSTEM ACCURACYACCURACY

50% OF TOTAL

90% OF TIME

Horizontal Vertical

4 m 4.3 m

8 m 11 m

GPS SYSTEM DESIGN RESOLVED THE GPS SYSTEM DESIGN RESOLVED THE MAJOR TECHNICAL ISSUESMAJOR TECHNICAL ISSUES

Technical IssuesTechnical Issues

Control segment vulnerabilityControl segment vulnerability

User jamming /spoofing User jamming /spoofing

User equipment costsUser equipment costs

Satellite lifetimeSatellite lifetime

Ionospheric corrections Ionospheric corrections

Solution

Atomic clocks

PRN & inertial integration

Digital signal and digital receiver

Redundant atomic clocks

Subsystem redundancy

Solid state amplifiers

Dual frequency - 1227 and 1575 MHz

GPS BLOCK I SATELLITEGPS BLOCK I SATELLITE

A KEY TO GPS SUCCESSA KEY TO GPS SUCCESS- Test- Test Results of the Rubidium Frequency Results of the Rubidium Frequency Standard - Standard -

Unacceptable

Acceptable

Data taken in vacuum at 35°C

SAMPLE TIME

AL

LA

N V

AR

IAN

CE

SIG

MA

10-12

10-13

10-14

10-0-0 10 1 10 2 10 3 10 4 10 5

S/N 1 Drift = - 5.77 x 10-14/DayS/N 2 Drift = - 1.45 x 10-15/DayS/N 4 Drift = 8 x 10-14/DayS/N 3 Drift = 4 x 10-14/DayS/N 7 Drift = 6 x 10-13/DayS/N 8 Drift = 6.8 x 10-13/Day

USE OF PSEUDOLITES AT USE OF PSEUDOLITES AT YUMAYUMA

Host Site

Host Site

Host Site

GPS RX

GPS RX

GPS RX

GT TXGT TX

GT TX

GPS TX(GT synch)

Control Display Unit (CDU)Data Link Equipment

Ground Transmitter (GT)

Control Interface

Timing

GPS Receiver

SV Simulator/Transmitter

Power Conditioning

PHASE I TEST RESULTS (1)PHASE I TEST RESULTS (1)- Spherical Error Probable - Spherical Error Probable (Meters) - (Meters) -

SATELLITE ORBITSSATELLITE ORBITS

• LEOLEO Low Earth Orbit Low Earth Orbit

• GEOGEO Geostationary OrbitGeostationary Orbit

• IGSOIGSO Inclined Geosynchronous OrbitInclined Geosynchronous Orbit

• ICOICO Intermediate Circular Orbit Intermediate Circular Orbit

• MEOMEO Medium Earth OrbitMedium Earth Orbit

• HEOHEO Highly Elliptical OrbitHighly Elliptical Orbit

• Sun synchronous orbitsSun synchronous orbits

HEO

GEO

IGSO

MEO, ICO

LEOSun

Sun synchronous orbit

~ ~

SIGNAL GENERATIONSIGNAL GENERATION

ModulationOscillator

Digital / Analog Signals

Data / Signal Input Signal Processing

Carrier Frequency

Information Signal

Output Signal

AmplifierAntenna

RF Signal

FREQUENCY AND FREQUENCY AND SPECTRA OF SPECTRA OF ELECTROMAGNETIC ELECTROMAGNETIC WAVESWAVES

Radar Frequency Bands

Frequency [GHz]

1 2 4 12.5 40 90 11018 26.58

KU KAL C X K E W

Frequency Bands

Frequency

3 kHz

30 300 30 30 300300 3GHz

3MHz

VHF SHFVLF LF MF HF UHF EHF

100 km

10 1 10 10 11 100mm

100m

Wavelength

S

SIGNAL MODULATIONSIGNAL MODULATION

• Technique to put information on a carrierTechnique to put information on a carrier

• Basic approaches:Basic approaches:

– Amplitude Amplitude A(t)A(t)= A= ACC sin( sin(CCt) At) AInfoInfo sin( sin(InfoInfot) t)

("Beating")("Beating")

– Phase Phase A(t)A(t)= A sin(= A sin(CCt + t + (t))(t))

• Adaption to transmit channelAdaption to transmit channel– Different frequenciesDifferent frequencies

– Carrier-to-noise ratioCarrier-to-noise ratio

AMPLITUDE AMPLITUDE MODULATIONMODULATION

• The ideal modulator is a multiplierThe ideal modulator is a multiplier

vC

vRF

vInfo

Carrier Frequency

Information Signal

Modulated Signal (Radio Frequency, RF)

Oscillator(Carrier)

Modulation Signal (Info)

Output

vC

vInfo

vRF

PHASE AND FREQUENCY PHASE AND FREQUENCY MODULATIONMODULATION• FM: Information signal changes frequency of the FM: Information signal changes frequency of the

carrier : f(t) ~ vcarrier : f(t) ~ vInfoInfo

• PM: Information signal changes phase of the carrier:PM: Information signal changes phase of the carrier:(t) ~ v(t) ~ vInfoInfo

• Examples FM - MusicExamples FM - Music

PM - Modem(Binary Phase Shift Keying):

vInfo

vRF

vC

vInfo

vRF

vC

MULTIPLE ACCESS MULTIPLE ACCESS SYSTEMSSYSTEMSAA Code Division Multiple Access (CDMA)Code Division Multiple Access (CDMA)

(= Spread Spectrum Multiple Access)(= Spread Spectrum Multiple Access)

S0 ... Power density B ... Bandwidth t ... time f ... frequency

tt

f0+ff0

C Time Division Multiple Access (TDMA)

B Frequency Division Multiple Access (FDMA) S0

S0

f

B

S0

f

t

B

S0

f

t

B

ttt0 + tt0

Channelno.

f

t

PRN code(channel)

GEOMETRY OF SIGNALSGEOMETRY OF SIGNALS

One-way ranging (GPS, GLONASS)

Measure t = / c = one-way time of travelCalculate = c t Two unsynchronised clocks

Measure t = 2 / c = two-way time of travel

Calculate = c t / 2One clock used to measure t

Two-way ranging(PRARE)

POLARISATIONPOLARISATION• Direction of polarisation = direction of electrical fieldDirection of polarisation = direction of electrical field

Examples Examples

Linear polarisationE = Ex = Direction of polarisation

Circular polarisationE = Ex + Ey = Direction of polarisation(e.g. GPS, GLONASS)

x

z

Direction of propagation

x

y

E

z

Direction of propagation

y

E

SS

GEOMETRY OF WAVE GEOMETRY OF WAVE PROPAGATIONPROPAGATION

Ground wavesGround waves ff < 1.6 MHz < 1.6 MHz

Sky waves Sky waves ff = 1.6 ... 30 MHz = 1.6 ... 30 MHz

Line of sight wavesLine of sight waves ff > 30 MHz > 30 MHz

Ionosphere

Ground waveGround waveGround waveGround wave

Sky wavesSky wavesSky wavesSky waves

Line of sight Line of sight waveswavesLine of sight Line of sight waveswaves

IonosphereIonosphereIonosphereIonosphere

Earth

DISTURBANCES AND LOSS OF DISTURBANCES AND LOSS OF POWER POWER AS FUNCTION OF FREQUENCYAS FUNCTION OF FREQUENCY• Atmospheric Atmospheric

losseslosses

16 to 16 to 9916 to 16 to 99

Atmospheric refraction

GHz1 10 102 103

10 2

10 1

dB/km

10 -1

10-2

Fog, Rain

Rainfall50 mm/h

f

Attenuationcoefficient

10 0

Tropopause

Troposphere

[km]

80

50

0

Ionosphere

Stratosphere

ATMOSPHERIC REFRACTION: ATMOSPHERIC REFRACTION: IONOSPHEREIONOSPHERE

• TEC measurement TEC measurement

(Total Electron Content)(Total Electron Content)

• Dispersive medium, 50 ... 1000 kmDispersive medium, 50 ... 1000 km

• Range error as function of Range error as function of

– FrequencyFrequency

– Sun activitySun activity

((11-year sunspot cycle)11-year sunspot cycle)

– Daytime / night-timeDaytime / night-timeIonosphereIonosphere

Geometric rangeGeometric range

Measured range

Observation site

Earth's surface

ATMOSPHERIC REFRACTION:ATMOSPHERIC REFRACTION:TROPOSPHERETROPOSPHERE• Two componentsTwo components

– Dry = f (Temp., Dry = f (Temp.,

Pressure) Pressure)

– Wet = f (Temp., Wet = f (Temp.,

HumidityHumidity))

• Local weather conditionsLocal weather conditions

Earth's surface

TroposphereTroposphere

Observation site

dry

hhwetwet 11 km 11 km

hdry 40 kmwet

MULTIPATHMULTIPATH- Reflections of radio signals - Reflections of radio signals from nearby objects -from nearby objects -

Antenna

Signal

GPS carrier phase: 0 ... 48 mm GPS pseudorange: A few meters ! Affects GPS C/A code more than P

code Solution

Choice of appropriate antenna Signal processing techniques

DOPPLER EFFECTDOPPLER EFFECT

Frequency

Time

PSEUDORANGE PSEUDORANGE MEASUREMENTMEASUREMENT

Time shift= PSEUDORANGE MEASUREMENT(in principle, time between transmission and reception is measured) Pseudorange = t · c

Transmitted codefrom satellite

Replica of satellite codegenerated in the receiver

CARRIER PHASE CARRIER PHASE MEASUREMENTMEASUREMENT

n unknown

0 2

0 360°180°

Resolution 0.1 ... 1 mm

POSITION POSITION DETERMINATION (1)DETERMINATION (1)

x

y

solution, no receiver clock error

L = toffset · c

solution considering receiver clock error determined by third satellite

PR1

PR2PR3

LL

L

PR1...3: measured

( x1 - x )2 + ( y1 - y )2 = ( L +

PR1)2

( x2 - x )2 + ( y2 - y )2 = ( L + PR2

)2

( x3 - x )2 + ( y3 - y )2 = ( L + PR3

)2

Two-dimensional example with receiver clock error

(x1 - x)2 + (y1 - y)2 + (z1 - z)2 + c T = PR1

(x2 - x)2 + (y2 - y)2 + (z2 - z)2 + c T = PR2

(x3 - x)2 + (y3 - y)2 + (z3 - z)2 + c T = PR3

(x4 - x)2 + (y4 - y)2 + (z4 - z)2 + c T = PR4

POSITION POSITION DETERMINATION (2)DETERMINATION (2)

Determined position is intersection point of all spheres

Three-dimensional case 4 satellites necessary 3 coordinates unknown1 time parameter unknown

Doppler EffectDoppler Effect

• The received signal has different frequencies The received signal has different frequencies from it was transmittedfrom it was transmitted

• The frequency difference depends on relative The frequency difference depends on relative velocity between transmitter and receivervelocity between transmitter and receiver f frr - f - ftt =-f =-ftt((’/c)’/c)

• Therefore: DOPLLER MEASURES VELOCITYTherefore: DOPLLER MEASURES VELOCITY

• Integration of Doppler shift over a period of Integration of Doppler shift over a period of time (ttime (t11:t:t22) => range difference) => range differenceN = -fN = -ftt/c(/c((t(t22)-)-(t(t11))))

Position Determination (3) - Position Determination (3) - Hyperbolic Hyperbolic

• If the distance difference of a point to If the distance difference of a point to another two points is a constant, this another two points is a constant, this point is on a hyperbolapoint is on a hyperbola

DOPPLER PRINCIPLE IN DOPPLER PRINCIPLE IN SATNAVSATNAVMeasurement PrincipleMeasurement PrincipleDoppler Positioning Doppler Positioning

(Translocation)(Translocation)

Intersection of two hyperboloids with Earth sphere

NN1212

NN2323tt11

tt22

tt33BB

Doppler Shift

frequency++

f + Doppler

f - Doppler

ff

TRANSIT SYSTEM TRANSIT SYSTEM

• 1959: Development started1959: Development started

• 1964: Operational for military use1964: Operational for military use

• 1967: Released for civil use1967: Released for civil use

• 1997: Phase-out1997: Phase-out

• Orbital height: 1075 km (LEO)Orbital height: 1075 km (LEO)

• Orbital period: 107 minOrbital period: 107 min

• Polar orbits i Polar orbits i 90° 90°

• Two carrier frequencies: fTwo carrier frequencies: f22 = 400, f = 400, f11 = 150 MHz = 150 MHz

• 2-d navigation system only2-d navigation system only

• Time interval between position fixes: 35 to 100 Time interval between position fixes: 35 to 100 minmin

Principle of TRANSITPrinciple of TRANSIT•Integrated Doppler Measurements:

N1 = f(x,y,z, Xs1, Xs2) N2 = f(x,y,z, Xs2, Xs3), N3 = f(x,y,z, Xs3, Xs4),………

•Solve for position x, y, z, subject to height control (zero for sea surface)

•Accuracy: Real time 200-400 m Multiple Passes: 1-2 m

The Global Positioning The Global Positioning SystemSystem

What is the Global What is the Global Positioning System?Positioning System?• NAVSTAR - Navigation Satellites with Timing and Ranging NAVSTAR - Navigation Satellites with Timing and Ranging

• Global, all weather, 24 hour, satellite based navigation, Global, all weather, 24 hour, satellite based navigation, positioning and timing systempositioning and timing system

• Developed by the US DOD, primarily for military purposesDeveloped by the US DOD, primarily for military purposes

• Passive ranging to satellites enables determination of Passive ranging to satellites enables determination of user’s position and velocity, and of timeuser’s position and velocity, and of time

• Positioning accuracy - 1mm to 20m depending onPositioning accuracy - 1mm to 20m depending ontype of receiver, user dynamics, type of receiver, user dynamics, observable and processing techniqueobservable and processing technique

• Two basic positioning servicesTwo basic positioning servicesPPS - Precise Positioning ServicePPS - Precise Positioning ServiceSPS - Standard Positioning ServiceSPS - Standard Positioning Service

GPS systemGPS system

• Three segmentsThree segments– Space SegmentSpace Segment

•Satellites in SpaceSatellites in Space– Ground SegmentGround Segment

•5 monitor station and one master 5 monitor station and one master control centrecontrol centre

– User SegmentUser Segment

•Any users with GPS receiversAny users with GPS receivers

GPS SYSTEMGPS SYSTEM

SpaceSegment

UserSegment

ControlSegment

ColoradoSprings

HawaiiKwajaleinAscension IslandDiegoGarcia

Monitor Stations

Global Positioning SystemGlobal Positioning System

• 24 Satellites

• 6 Orbital planes

• 55° Inclination

• 20200 km above the Earth

• 12 hour orbits

Ground SegmentGround Segment

• Monitor Station (MS) - 5Monitor Station (MS) - 5Hawaii, Colorado Springs, Ascension IslandHawaii, Colorado Springs, Ascension IslandDiego Garcia, KwajalienDiego Garcia, Kwajalien

Receive satellite signals and relay to MCSReceive satellite signals and relay to MCS

All except Hawaii have ground antennas to All except Hawaii have ground antennas to communicate communicate with satelliteswith satellites

• Master Control Station (MCS)Master Control Station (MCS)Falcon AFB, Colorado SpringsFalcon AFB, Colorado Springs

Satellite ephemerides and clock parameters Satellite ephemerides and clock parameters estimatedestimated

Ground SegmentGround Segment

Colorado SpringsColorado Springs

AscensionAscension Diego GarciaDiego Garcia

HawaiiKwajaleinKwajalein

• User measures distance to four satellitesUser measures distance to four satellites

• Satellites transmit their positions in orbitSatellites transmit their positions in orbit

• User solves for position (X,Y,Z or User solves for position (X,Y,Z or , h) and , h) and clock error clock error tt

Global Positioning System Global Positioning System ConceptConcept

GPS Range MeasurementGPS Range Measurement

• One-way range (distance) between satellite and receiverOne-way range (distance) between satellite and receiver

• Measurement of time-of-flight of coded signalsMeasurement of time-of-flight of coded signals

• Each satellite has a unique code (Gold Codes)Each satellite has a unique code (Gold Codes)

• Synchronised clocks in receiver and satellitesSynchronised clocks in receiver and satellites

• Receiver attempts to match received code with its own Receiver attempts to match received code with its own codecode

• Pseudo-rangePseudo-rangePure geometrical range corrupted byPure geometrical range corrupted by

Clock offsetsClock offsetsAtmospheric errorsAtmospheric errorsOther error sourcesOther error sources

GPS Signal StructureGPS Signal Structure

• Two L band carriersTwo L band carriersL1L1 1575.42 MHz1575.42 MHzL2L2 1227.60 MHz1227.60 MHz

• Two spread spectrum modulated timing codesTwo spread spectrum modulated timing codesC/A codeC/A code 1.023 MHz1.023 MHz 1ms1ms L1 onlyL1 onlyP codeP code 10.23 MHz10.23 MHz 38 weeks38 weeks L1 L1

and L2and L2

• Navigation messageNavigation message50 bps50 bps25 pages, 5 subframes25 pages, 5 subframes

GPS Signal StructureGPS Signal Structure

GPS Pseudo-range GPS Pseudo-range ObservableObservable• Main navigation observableMain navigation observable

• Code correlation of timing codesCode correlation of timing codes

• Very simple, very robustVery simple, very robust

• Stand alone positioningStand alone positioning

• Standard Positioning ServiceStandard Positioning ServiceCoarse/Acquisition (C/A) code Coarse/Acquisition (C/A) code 20 metres20 metres

• Precise Positioning ServicePrecise Positioning ServicePrecision (P/Y) codePrecision (P/Y) code 10 metres10 metres

Differential GPSDifferential GPS

DGPS correction terms Differential transmitter

DGPS reference receiver

Differential GPS (DGPS)Differential GPS (DGPS)

• Relative Positioning using pseudo-rangesRelative Positioning using pseudo-ranges

• Receiver at a known locationReceiver at a known location

• Real-timeReal-timeTransmit measured errors in pseudo-Transmit measured errors in pseudo-

ranges to remote ranges to remote (mobile) user(mobile) user

• Post-processingPost-processingSingle difference of pseudo-rangesSingle difference of pseudo-ranges

• removes most ephemeris, atmospheric removes most ephemeris, atmospheric and satellite clock errors and satellite clock errors

GPS Carrier Phase GPS Carrier Phase ObservableObservable• Main surveying (high precision) observableMain surveying (high precision) observable

• Phase measurement on carrier signals (L1 & L2)Phase measurement on carrier signals (L1 & L2)

• 19cm or 24cm wavelength - resolution few mm19cm or 24cm wavelength - resolution few mm

• Integer ambiguityInteger ambiguity

• Relative positioningRelative positioning

• Single difference / double differenceSingle difference / double difference

• More difficult to access, measure and processMore difficult to access, measure and process

• Static and kinematic processingStatic and kinematic processing

Carrier Phase TrackingCarrier Phase Tracking

At Lock-on

At a Later Epoch

Carrier Phase

Carrier Phase

Integer Ambiguity

Integer Ambiguity

Double Difference Phase Double Difference Phase ObservableObservable

S T

A B

Observable = (TB-TA) - (SB-SA)Removes ephemeris, clock and atmospheric errors

GPS Pseudo-Range GPS Pseudo-Range PositioningPositioning

• Absolute PositioningAbsolute PositioningPseudo-ranges measured at one receiverPseudo-ranges measured at one receiverStandard Positioning ServiceStandard Positioning Service - 20m- 20mPrecise Positioning Service - 10mPrecise Positioning Service - 10mTime averaging - over three days with SPS ~ 1 mTime averaging - over three days with SPS ~ 1 m

• Differential GPSDifferential GPSPseudo-range measurements at two (or more) pointsPseudo-range measurements at two (or more) pointsOne receiver at know ‘reference station’One receiver at know ‘reference station’Cancels common errorsCancels common errorsRelative positioningRelative positioningData link - terrestrial or satelliteData link - terrestrial or satelliteReal time accuracy of ~ 1 - 5mReal time accuracy of ~ 1 - 5m

• Network / Wide Area DGPSNetwork / Wide Area DGPSMultiple DGPS reference stationsMultiple DGPS reference stationsCover large geographical areaCover large geographical area

GPS Carrier Phase SurveyingGPS Carrier Phase Surveying• Static GPSStatic GPS

Measure carrier phase simultaneous at two or more pointsMeasure carrier phase simultaneous at two or more pointsStatic surveying (>40mins for each line)Static surveying (>40mins for each line)Relative positioning of Relative positioning of fewfew cm and cm and fewfew ppm ppm

• Fiducial GPS Fiducial GPS mm over thousands of kilometresmm over thousands of kilometresPrecise orbital & atmospheric modellingPrecise orbital & atmospheric modelling

• Fast StaticFast StaticRapid/Fast initialisation techniquesRapid/Fast initialisation techniquesFor short lines only a few minutes of data requiredFor short lines only a few minutes of data required

• Kinematic GPS surveyingKinematic GPS surveyingCarrier phase at two or more receiversCarrier phase at two or more receiversOne receiver stationary, one One receiver stationary, one mobile mobile from point to pointfrom point to point

Few centimetres in a few secondsFew centimetres in a few secondsFast / On-the-fly initialisationFast / On-the-fly initialisationCentimetric navigationCentimetric navigation

GPS LimitationsGPS Limitations• Sky VisibilitySky Visibility

Canyons (natural and urban), quarriesCanyons (natural and urban), quarriesTree coverTree coverElevation mask 20º to 30º Elevation mask 20º to 30º

• MultipathMultipathCareful positioning of sitesCareful positioning of sitesSpecialised receivers, Choke ring antennas Specialised receivers, Choke ring antennas

• InterferenceInterferenceAccidental - TV, Radio, mobile phoneAccidental - TV, Radio, mobile phoneIntentional - jammingIntentional - jamming

• CommunicationsCommunicationsReal Time Kinematic (RTK)Real Time Kinematic (RTK)Differential (DGPS)Differential (DGPS)

• Robustness of carrier phase solutionRobustness of carrier phase solutionAmbiguity resolution, cycle slipsAmbiguity resolution, cycle slipsRange between reference stations and userRange between reference stations and user

GPS Operational CapabilityGPS Operational Capability

• Initial Operational Capability (IOC)Initial Operational Capability (IOC)Declared operational for use by the civil communityDeclared operational for use by the civil communityDecember 8 1993December 8 1993Anti-Spoofing (AS) - January 31 1994Anti-Spoofing (AS) - January 31 1994Selective Availability (SA) tests discontinued Selective Availability (SA) tests discontinued

• Full Operational Capability (FOC)Full Operational Capability (FOC)Declared fully operational 27 April 1995Declared fully operational 27 April 199524 block II/IIA satellites24 block II/IIA satellitesTrials and experiments completedTrials and experiments completed

Presidential Decision Presidential Decision DirectiveDirective• Presidential Decision Directive PDD NSTC-6Presidential Decision Directive PDD NSTC-6

• 28 March 199628 March 1996

• Policy GuidelinesPolicy GuidelinesProvide SPS continuous world-wide, free of user Provide SPS continuous world-wide, free of user

chargeschargesDiscontinue SA within a decade (by 2006)Discontinue SA within a decade (by 2006)*Suspend of SA on May 2001*Suspend of SA on May 2001

• NAVWAR - GPS Security ProgramNAVWAR - GPS Security Program

• Joint management Joint management Interagency GPS Executive BoardInteragency GPS Executive BoardDept. of Defense/Transportation/State/CommerceDept. of Defense/Transportation/State/Commerce

• GPS will remain responsive to National Command AuthoritiesGPS will remain responsive to National Command Authorities

GPS ModernisationGPS Modernisation• More satellites in constellation - increased integrityMore satellites in constellation - increased integrity

– 30-3630-36

• Auto-nav operation – up to six monthsAuto-nav operation – up to six months

• More ground tracking stations – better orbitMore ground tracking stations – better orbit

• Increased radiated power - military spot beamIncreased radiated power - military spot beam

• Aft facing antennas for GEO satellite usersAft facing antennas for GEO satellite users

• Military use of pseudo-litesMilitary use of pseudo-lites

• NAVWAR Enhanced Military User Equipment (UE)NAVWAR Enhanced Military User Equipment (UE)

• Separate military signal Separate military signal

• 2nd / 3rd civil signal agreements2nd / 3rd civil signal agreements

• LLMM (Link Military) project (Link Military) project

– Re-use of current spectrum, addition on new (M) codeRe-use of current spectrum, addition on new (M) code

– First possible launch is Option 2 of Block IIF (now 2007)First possible launch is Option 2 of Block IIF (now 2007)

2nd / 3rd Coded Civilian 2nd / 3rd Coded Civilian SignalsSignals• March 98 agreement to implement two March 98 agreement to implement two

additional civil GPS signalsadditional civil GPS signals

• January 99 ‘budget’ and frequencies January 99 ‘budget’ and frequencies announcedannounced

• L2 carrier will have a C/A codeL2 carrier will have a C/A code

• Third frequency, L5, 1176.45 MHz, in Third frequency, L5, 1176.45 MHz, in existing ARNS band existing ARNS band

• L5 carrier with VS code as Safety-of-Life L5 carrier with VS code as Safety-of-Life signalsignal

GPS and GLNOSS Frequency GPS and GLNOSS Frequency BandBand

GPS SignalGPS Signal

Other Satellite SystemsOther Satellite Systems

• GLONASSGLONASS• Compass (Beidou)Compass (Beidou)• GalileoGalileo• Augmentation systemsAugmentation systems

– SBASSBAS•WAAS, EGNOSWAAS, EGNOS

– GBASGBAS

ContentsContents

• Introduction (week 1)Introduction (week 1)• GPS observables (week 2)GPS observables (week 2)• Reference Systems and Satellite Orbits (week3)Reference Systems and Satellite Orbits (week3)• Positioning with Pseudorange (week 4)Positioning with Pseudorange (week 4)• GPS Errors and Modelling (week5)GPS Errors and Modelling (week5)• Positioning with Carrier Phase (week 6)Positioning with Carrier Phase (week 6)• High Precision positioning (week 7)High Precision positioning (week 7)• GBAS and SBAS (week8)GBAS and SBAS (week8)• Terrestrial Navigation systems (week 9)Terrestrial Navigation systems (week 9)• Inertial Navigation Systems (week 10)Inertial Navigation Systems (week 10)• System Integration (week 11)System Integration (week 11)• Project Presentation (week 12-14)Project Presentation (week 12-14)

Assessments (50%)Assessments (50%)

• Report OneReport One– GPS Errors and Correction Models GPS Errors and Correction Models

• IonosphereIonosphere•Troposphere Troposphere •MultipathMultipath

• Report TwoReport Two– Precise Point Positioning Methods and recePrecise Point Positioning Methods and rece

nt developmentsnt developments

Final Project (50%)Final Project (50%)Final Project (50%)Final Project (50%)• TopicTopic

– Design an integrated navigation system for a Design an integrated navigation system for a specified application related to your work or specified application related to your work or experience experience

• Report Submission (week 14)Report Submission (week 14)– Report (10-15 pages)Report (10-15 pages)

• Purposes of the applicationPurposes of the application

• Navigation RequirementsNavigation Requirements

• System Design System Design

• Analysis on performances of the designed Analysis on performances of the designed systemsystem

• Discussion and conclusionDiscussion and conclusion

• Presentation (week 12-14)Presentation (week 12-14)– Powerpoint Slides (20 min)Powerpoint Slides (20 min)

• TopicTopic– Design an integrated navigation system for a Design an integrated navigation system for a

specified application related to your work or specified application related to your work or experience experience

• Report Submission (week 14)Report Submission (week 14)– Report (10-15 pages)Report (10-15 pages)

• Purposes of the applicationPurposes of the application

• Navigation RequirementsNavigation Requirements

• System Design System Design

• Analysis on performances of the designed Analysis on performances of the designed systemsystem

• Discussion and conclusionDiscussion and conclusion

• Presentation (week 12-14)Presentation (week 12-14)– Powerpoint Slides (20 min)Powerpoint Slides (20 min)