intro_gps tejas

8/7/2019 intro_gps tejas

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Introduction to theIntroduction to the

Global Positioning SystemGlobal Positioning System

Mahatma Gandhi MissionMahatma Gandhi MissionCollege Of EngineeringCollege Of Engineering


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What is the GPS?What is the GPS?

TheThe Global Positioning SystemGlobal Positioning System ((GPSGPS) is) isa spacea space--basedbased global navigation satelliteglobal navigation satellite

systemsystem (GNSS) that provides reliable(GNSS) that provides reliablelocationlocation and time informationand time information

It is maintained by theIt is maintained by the United StatesUnited States

government and is freely accessible bygovernment and is freely accessible by

anyone with a GPS receiver.anyone with a GPS receiver.


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History of the GPSHistory of the GPS

19691969Defense Navigation SatelliteDefense Navigation Satellite

System (DNSS) formedSystem (DNSS) formed

19731973NAVSTAR Global PositioningNAVSTAR Global PositioningSystem developedSystem developed

19781978first 4 satellitesfirst 4 satellites

launchedlaunched

Delta rocket launchDelta rocket launch


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History of the GPSHistory of the GPS

1993199324th satellite24th satellite

launched; initiallaunched; initial

operational capabilityoperational capability

19951995full operationalfull operational

capabilitycapability

May 2000May 2000MilitaryMilitary

accuracy available toaccuracy available toall usersall users


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The GPS ConstellationThe GPS Constellation


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Components of the SystemComponents of the System

Space segmentSpace segment 24 satellite vehicles24 satellite vehicles

Six orbital planesSix orbital planes Inclined 55Inclined 55oo with respect towith respect to

equatorequator Orbits separated by 60Orbits separated by 60oo

20,200 km elevation above20,200 km elevation aboveEarthEarth

Orbital period of 11 hr 55Orbital period of 11 hr 55

minmin Five to eight satellitesFive to eight satellites

visible from any point onvisible from any point onEarthEarth

Block I Satellite VehicleBlock I Satellite Vehicle


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User segmentUser segment

GPS antennas & receiver/processorsGPS antennas & receiver/processors

PositionPosition

VelocityVelocity

Precise timingPrecise timing

Used byUsed by

AircraftAircraft Ground vehiclesGround vehicles

ShipsShips

IndividualsIndividuals


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Ground control segmentGround control segment

Master control stationMaster control station Schreiver AFB, ColoradoSchreiver AFB, Colorado

Five monitor stationsFive monitor stations

Three ground antennasThree ground antennas Backup control systemBackup control system


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GPS Communication and ControlGPS Communication and Control


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How does GPS work?How does GPS work?

Satellite rangingSatellite ranging

Satellite locationsSatellite locations

Satellite to user distanceSatellite to user distance

Need four satellites to determine positionNeed four satellites to determine position

Distance measurementDistance measurement

Radio signal traveling at speed of lightRadio signal traveling at speed of light Measure time from satellite to userMeasure time from satellite to user

LowLow--tech simulationtech simulation


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PseudoPseudo--Random CodeRandom Code

Complex signalComplex signal

Unique to eachUnique to each

satellitesatellite

All satellites useAll satellites use

same frequencysame frequency

Amplified byAmplified byinformation theoryinformation theory

EconomicalEconomical


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Distance to a satellite is determined by measuring howDistance to a satellite is determined by measuring howlong a radio signal takes to reach us from that satellite.long a radio signal takes to reach us from that satellite.

To make the measurement we assume that both theTo make the measurement we assume that both thesatellite and our receiver are generating the samesatellite and our receiver are generating the same

pseudopseudo--random codes at exactly the same time.random codes at exactly the same time.

By comparing how late the satellite's pseudoBy comparing how late the satellite's pseudo--randomrandomcode appears compared to our receiver's code, wecode appears compared to our receiver's code, wedetermine how long it took to reach us.determine how long it took to reach us.

Multiply that travel time by the speed of light and you'veMultiply that travel time by the speed of light and you'vegot distance.got distance.

HighHigh--tech simulationtech simulation


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Accurate timing is the key to measuringAccurate timing is the key to measuring

distance to satellites.distance to satellites.

Satellites are accurate because they haveSatellites are accurate because they havefour atomic clocks ($100,000 each) onfour atomic clocks ($100,000 each) onboard.board.

Receiver clocks don't have to be tooReceiver clocks don't have to be too

accurate because an extra satellite rangeaccurate because an extra satellite range

measurement can remove errors.measurement can remove errors.


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To use the satellites as references for rangeTo use the satellites as references for rangemeasurements we need to know exactly where they are.measurements we need to know exactly where they are.

GPS satellites are so high up their orbits are veryGPS satellites are so high up their orbits are verypredictable.predictable.

All GPS receivers have an almanac programmed intoAll GPS receivers have an almanac programmed intotheir computers that tells them where in the sky eachtheir computers that tells them where in the sky eachsatellite is, moment by moment.satellite is, moment by moment.

Minor variations in their orbits are measured by theMinor variations in their orbits are measured by the

Department of Defense.Department of Defense. The error information is sent to the satellites, to beThe error information is sent to the satellites, to be

transmitted along with the timing signals.transmitted along with the timing signals.


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GPS Position DeterminationGPS Position Determination


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GPS NavigationGPS Navigation


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System PerformanceSystem Performance

Standard PositioningStandard Positioning

SystemSystem 100 meters horizontal accuracy100 meters horizontal accuracy

156 meters vertical accuracy156 meters vertical accuracy Designed for civilian useDesigned for civilian use

No user fee or restrictionsNo user fee or restrictions

Precise PositioningPrecise Positioning

SystemSystem 22 meters horizontal accuracy22 meters horizontal accuracy

27.7 meters vertical accuracy27.7 meters vertical accuracy

Designed for military useDesigned for military use


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Selective availabilitySelective availability

Intentional degradation of signalIntentional degradation of signal

Controls availability of systems full capabilitiesControls availability of systems full capabilities Set to zero May 2000Set to zero May 2000

ReasonsReasons

Enhanced 911 serviceEnhanced 911 service

Car navigationCar navigation

Adoption of GPS time standardAdoption of GPS time standard

RecreationRecreation


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The earth's ionosphere and atmosphereThe earth's ionosphere and atmosphere

cause delays in the GPS signal thatcause delays in the GPS signal that

translate into position errors.translate into position errors.

Some errors can be factored out usingSome errors can be factored out using

mathematics and modeling.mathematics and modeling.

The configuration of the satellites in theThe configuration of the satellites in the

sky can magnify other errors.sky can magnify other errors.

Differential GPSDifferential GPS can reduce errors.can reduce errors.


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Message FormatMessage Format

Each GPS satellite continuouslyEach GPS satellite continuously

broadcasts abroadcasts a navigation messagenavigation message at a rateat a rate

of 50 bits per secondof 50 bits per second

Each complete message is composed ofEach complete message is composed of

3030--secondsecond framesframes

All satellites broadcast at the sameAll satellites broadcast at the same

frequencies. Signals are encoded usingfrequencies. Signals are encoded using

code division multiple accesscode division multiple access (CDMA)(CDMA)


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GPS Message FormatGPS Message Format

Sub frames DescriptionSub frames Description

1 Satellite clock ,GPS time1 Satellite clock ,GPS time

relationshiprelationship22--33 EphemerisEphemeris

(precise satellite orbit)(precise satellite orbit)

44--55 Almanac componentAlmanac component(satellite network synopsis,(satellite network synopsis,error correction)error correction)


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Satellite frequencies

Band Frequency Description

L1 1575.42 MHz

Course-acquisition (C/A) and

encrypted precision P(Y) codes,

plus the L1 civilian (L1C) and

military (M) codes on future

Block III satellites.

L2 1227.60 MHz

P(Y) code, plus the L2C and

military codes on the Block IIR-

M and newer satellites.

L3 1381.05 MHz

Used for nuclear detonation

(NUDET) detection.

L4 1379.913 MHzBeing studied for additional

ionospheric correction.

L5 1176.45 MHzProposed for use as a civilian

safety-of-life (SoL) signal.


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Application of GPS TechnologyApplication of GPS Technology

LocationLocation -- determining a basic positiondetermining a basic position

NavigationNavigation -- getting from one location togetting from one location to

anotheranother TrackingTracking -- monitoring the movement ofmonitoring the movement of

people and thingspeople and things

MappingMapping -- creating maps of the worldcreating maps of the world TimingTiming -- bringing precise timing to thebringing precise timing to the

worldworld


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Application of GPS TechnologyApplication of GPS Technology

Private and recreationPrivate and recreation

Traveling by carTraveling by car

Hiking, climbing, bikingHiking, climbing, biking

Vehicle controlVehicle control

Mapping, survey, geologyMapping, survey, geology

GeotaggingGeotagging

AgricultureAgriculture

GPS Aircraft TrackingGPS Aircraft Tracking General and commercialGeneral and commercial

SpacecraftSpacecraft

MaritimeMaritime


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Military Uses for the GPSMilitary Uses for the GPS

Target tracking: Missile and projectile guidanceTarget tracking: Missile and projectile guidance

Search and Rescue: Downed pilots can beSearch and Rescue: Downed pilots can belocated fasterlocated faster

Reconnaissance: Patrol movement can beReconnaissance: Patrol movement can bemanaged more closelymanaged more closely

GPS satellites carry setGPS satellites carry set

of nuclear detonationof nuclear detonation

detectorsdetectors

Navigation: GPS allowsNavigation: GPS allows

soldiers find objectivessoldiers find objectives


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Restrictions On Civilian UseRestrictions On Civilian Use

The U.S. Government controls the export ofThe U.S. Government controls the export ofsome civilian receiverssome civilian receivers

All GPS receivers capable of functioning aboveAll GPS receivers capable of functioning above

1818 kilometers (11kilometers (11 mi) altitude and 515mi) altitude and 515 metresmetresper second (1,001per second (1,001 knkn)are classified as)are classified as munitionsmunitions(weapons) for which(weapons) for which U.S. State DepartmentU.S. State Departmentexport licensesexport licenses are requiredare required

These limits attempt to prevent use of a receiverThese limits attempt to prevent use of a receiverin ain a ballistic missileballistic missile


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Future ScopeFuture Scope

The future of global positioning system isThe future of global positioning system is

bright as predictions range from its'bright as predictions range from its'

increased usage to expansion into newincreased usage to expansion into new

areas of applicationareas of application

It is estimated that there will be 50 millionIt is estimated that there will be 50 million

users of theusers of the global positioning systemglobal positioning system byby

20102010


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ConclusionConclusion

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