Gps

Global Positioning SystemGlobal Positioning System

What is the GPS?What is the GPS?The The Global Positioning SystemGlobal Positioning System ( (GPSGPS) is ) is

a space-based satellite navigation system a space-based satellite navigation system that provides location and time information that provides location and time information in all weather, anywhere on or near the in all weather, anywhere on or near the Earth, where there is an Earth, where there is an unobstructed line of sight to unobstructed line of sight to four or more GPS satellitesfour or more GPS satellites

Developed by Developed by Department Department of Defenseof Defense

History of the GPSHistory of the GPS1973—The GPS project was developed to 1973—The GPS project was developed to

overcome the limitations of previous overcome the limitations of previous navigation systemsnavigation systems

1994—GPS Was Created and realized by 1994—GPS Was Created and realized by U.S. Department of Defense (DoD) U.S. Department of Defense (DoD) and was originally run with 24  and was originally run with 24 

satellites satellites

History of the GPSHistory of the GPS 1993—Indicating a 1993—Indicating a

full constellation (24 full constellation (24 satellites) was satellites) was availableavailable

1995—full operational 1995—full operational capabilitycapability

May 2000—Military May 2000—Military accuracy available to accuracy available to all usersall users

Components of the SystemComponents of the SystemSpace segmentSpace segment 24 satellite vehicles24 satellite vehicles Six orbital planesSix orbital planes

Inclined 55Inclined 55o o with respect to with respect to equatorequator

Orbits separated by 60Orbits separated by 60oo

20,200 km elevation above 20,200 km elevation above EarthEarth

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

Five to eight satellites Five to eight satellites visible from any point on visible from any point on EarthEarth

The GPS ConstellationThe GPS Constellation

GPS Satellite VehicleGPS Satellite Vehicle Four atomic clocksFour atomic clocks Three nickel-cadmium Three nickel-cadmium

batteriesbatteries Two solar panelsTwo solar panels

Battery chargingBattery charging Power generationPower generation 1136 watts1136 watts

S band antenna—satellite S band antenna—satellite controlcontrol

12 element L band antenna—12 element L band antenna—user communicationuser communication

Block IIF satellite vehicle Block IIF satellite vehicle (fourth (fourth generation)generation)

GPS Satellite VehicleGPS Satellite Vehicle

WeightWeight 2370 pounds2370 pounds

HeightHeight 16.25 feet16.25 feet

WidthWidth 38.025 feet including 38.025 feet including

wing spanwing span

Design life—10 yearsDesign life—10 years

Components of the SystemComponents of the SystemUser segmentUser segment GPS antennas & receiver/processorsGPS antennas & receiver/processors PositionPosition VelocityVelocity Precise timingPrecise timing Used byUsed by

AircraftAircraft Ground vehiclesGround vehicles ShipsShips IndividualsIndividuals

Components of the SystemComponents of the System

Ground control segmentGround control segmentMaster control stationMaster control station

Schreiver AFB, ColoradoSchreiver AFB, ColoradoFive monitor stationsFive monitor stationsThree ground antennasThree ground antennasBackup control systemBackup control system

GPS Communication and ControlGPS Communication and Control

GPS Ground Control StationsGPS Ground Control Stations

How does GPS work?How does GPS work?

Satellite rangingSatellite rangingSatellite locationsSatellite locationsSatellite to user distanceSatellite to user distanceNeed four satellites to determine positionNeed four satellites to determine position

Distance measurementDistance measurementRadio signal traveling at speed of lightRadio signal traveling at speed of lightMeasure time from satellite to userMeasure time from satellite to user

Low-tech simulationLow-tech simulation

How does GPS work?How does GPS work?

Pseudo-Random CodePseudo-Random Code Complex signalComplex signal Unique to each Unique to each

satellitesatellite All satellites use All satellites use

same frequencysame frequency ““Amplified” by Amplified” by

information theoryinformation theory EconomicalEconomical

How does GPS work?How does GPS work? Distance to a satellite is determined by measuring how Distance to a satellite is determined by measuring how

long 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 the To make the measurement we assume that both the

satellite and our receiver are generating the same satellite and our receiver are generating the same pseudo-random codes at exactly the same time. pseudo-random codes at exactly the same time.

By comparing how late the satellite's pseudo-random By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we code appears compared to our receiver's code, we determine 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've Multiply that travel time by the speed of light and you've got distance. got distance.

High-tech simulationHigh-tech simulation

How does GPS work?How does GPS work?

Accurate timing is the key to measuring Accurate timing is the key to measuring distance to satellites.distance to satellites.

Satellites are accurate because they have Satellites are accurate because they have four atomic clocks ($100,000 each) on four atomic clocks ($100,000 each) on board. board.

Receiver clocks don't have to be too Receiver clocks don't have to be too accurate because an extra satellite range accurate because an extra satellite range measurement can remove errors. measurement can remove errors.

How does GPS work?How does GPS work? To use the satellites as references for range To use the satellites as references for range

measurements 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 very GPS satellites are so high up their orbits are very

predictable. predictable. All GPS receivers have an almanac programmed into All GPS receivers have an almanac programmed into

their computers that tells them where in the sky each their computers that tells them where in the sky each satellite is, moment by moment. satellite is, moment by moment.

Minor variations in their orbits are measured by the Minor variations in their orbits are measured by the Department of Defense. Department of Defense.

The error information is sent to the satellites, to be The error information is sent to the satellites, to be transmitted along with the timing signals. transmitted along with the timing signals.

GPS Position DeterminationGPS Position Determination

System PerformanceSystem Performance Standard Positioning Standard 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 Positioning Precise 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

System PerformanceSystem Performance

Selective availabilitySelective availability Intentional degradation of signalIntentional degradation of signal Controls availability of system’s full capabilitiesControls availability of system’s full capabilities Set to zero May 2000Set to zero May 2000 ReasonsReasons

Car navigationCar navigation Adoption of GPS time standardAdoption of GPS time standard RecreationRecreation

System PerformanceSystem Performance

The earth's ionosphere and atmosphere The earth's ionosphere and atmosphere cause delays in the GPS signal that cause delays in the GPS signal that translate into position errors. translate into position errors.

Some errors can be factored out using Some errors can be factored out using mathematics and modeling. mathematics and modeling.

The configuration of the satellites in the The configuration of the satellites in the sky can magnify other errors. sky can magnify other errors.

Differential GPS can reduce errors.Differential GPS can reduce errors.

Application of GPS TechnologyApplication of GPS Technology

Location - determining a basic positionLocation - determining a basic positionNavigation - getting from one location to Navigation - getting from one location to

another another Tracking - monitoring the movement of Tracking - monitoring the movement of

people and things people and things Mapping - creating maps of the world Mapping - creating maps of the world Timing - bringing precise timing to the Timing - bringing precise timing to the

world world

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 English Channel TunnelEnglish Channel Tunnel AgricultureAgriculture AviationAviation

General and commercialGeneral and commercial SpacecraftSpacecraft

MaritimeMaritime

GPS NavigationGPS Navigation

Military Uses for the GPSMilitary Uses for the GPS

Operation Desert StormOperation Desert Storm Featureless terrainFeatureless terrain Initial purchase of 1000 portable commercial Initial purchase of 1000 portable commercial

receiversreceivers More than 9000 receivers in use by end of the More than 9000 receivers in use by end of the

conflictconflict Foot soldiersFoot soldiers VehiclesVehicles AircraftAircraft Marine vesselsMarine vessels

Handheld GPS ReceiversHandheld GPS Receivers LowranceLowrance iWay350ciWay350c

This is great value for This is great value for a full-featured turn-by a full-featured turn-by turn GPS navigation turn GPS navigation system.system.

Cobra NavOne 450Cobra NavOne 450

This system's 5-inch This system's 5-inch screen and integrated screen and integrated live traffic data set it live traffic data set it apart from other GPS apart from other GPS devices.devices.

GPS Operation GPS Operation

““Waypoint” or “Landmark”Waypoint” or “Landmark” ““Track” or “Heading”Track” or “Heading” ““Bearing”Bearing” CDICDI RouteRoute MarkMark GOTOGOTO

Mobile phone GPS trackingMobile phone GPS tracking