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8/7/2019 global positioning sysstem
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Presented By-
SANDIP KUMAR PATTANAIK
ROLL NO.---0401101169
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1. Introduction.2. History of GPS3. Components of GPS
4. How does GPS work5. GPS capabilities6. Errors in GPS system.
7. Parts of GPS Network8. Application of GPS system9. Conclusion
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INTRODUCTION
y The Global Positioning System (GPS) is a satellite-basednavigation system made up of a network of 24 satellites
that orbit the Earth and make it possible for people withground receivers to pinpoint their geographic location
y GPS satellites circle the earth twice a day in a veryprecise orbit and transmit signal information to earth.
y GPS satellites orbit around 11000 nautical miles abovethe Earth. They are monitored continuously at the
ground station around the world.
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United States Department of Defense developed thesystem, officially named NAVSTAR GPS (NavigationSignal Timing and Ranging GPS), and the satelliteconstellation is managed by the 50th Space Wing atSchriever Air Force Base. Although the cost ofmaintaining the system is approximately US$400million per year, including the replacement of aging
satellites, GPS is available for free use in civilianapplications as a public good.
In late 2005, the first in a series of next-generationGPS satellites was added to the constellation, offering
several new capabilities. There is also another GPS system in Russia known as
GLONASS which may prove complementary toNAVSTAR
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HISTORY OF GPS
yGPS was first launched in the year 1978.
y The first 10 satellites launched weredevelopmental satellite.
y The launch of 24th satellite was completed in
1994.
y The Third generation satellite, block IIR werelaunched in 1997.
y
The Next generation, Block IIF, is launched inlate 2005.
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VISUAL EXAMPLE OF GPS
y A visual example of the GPS constellation in motion with the Earthrotating. Notice how the number of satellites in view from a givenpoint on the Earth's surface, in this example at 45N, changes with
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Components of the GPS
Space Segment Control Segment User Segment
GPS
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Space Segment:
y 24 GPS spacevehicles(SVs).
y Satellites orbit theearth in 12 hrs.
y 6 orbital planesinclined at 55 degreeswith the equator.
y Th
is constellationprovides 5 to 8 SVsfrom any point on theearth.
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Paul Lammertsma
equator
orbital plane20,200 km
55
6 planes
Configuration
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Control segment:
y The control segmentcomprises of 5 stations.
y They measure thedistances of the overheadsatellites every 1.5 secondsand send the correcteddata to Master control.
y Here the satellite orbit,clock performance andhealth of the satellite aredetermined anddetermines whether
repositioning is required.y This information is sent to
the three uplink stations
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User Segment:y It consists of receivers that decode the signals from the
satellites.
y The receiver performs following tasks:y Selecting one or more satellites
y Acquiring GPS signals
y Measuring and tracking
y Recovering navigation data
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The Global Positioning System (GPS) is a satellite-basednavigation system made up of a network of 24 satellites
placed into the orbit of earth.
GPS was originally intended for military applications, butlater on the government made the system available for civilianuse.
GPS works in any weather conditions, anywhere in the world,24 hours a day.
There are no subscription fees or setup charges to use GPS.
GPS satellites circle the earth twice a day in a very preciseorbit and transmit signal information to earth.
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United States Department of Defense developed the system,officially named NAVSTAR GPS (Navigation Signal Timing and
Ranging GPS), and the satellite constellation is managed by the
50th Space Wing at Schriever Air Force Base. Although the cost of
maintaining the system is approximately US$400 million per year,
including the replacement of aging satellites, GPS is available forfree use in civilian applications as a public good.
In late 2005, the first in a series of next-generation GPS satellites
was added to the constellation, offering several new capabilities.
There is also another GPS system in Russia known as GLONASS
which may prove complementary to NAVSTAR
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Here are some other interesting facts about the GPSsatellites (also called NAVSTAR, the official U.S.Department of Defense name for GPS):
The first GPS satellite was launched in 1978. A full constellation of 24 satellites was achieved in
1994. Each satellite is built to last about 10 years.Replacements are constantly being built andlaunched into orbit.
A GPS satellite weigh
s approximately 2,000 poundsand is about 17 feet across with the solar panelsextended.
Transmitter power is only 50 watts or less.
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A Ground Trackmap shows how this
scheme covers the Earth.
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Space Segment:
y 24 GPS spacevehicles(SVs).
y Satellites orbit theearth in 12 hrs.
y 6 orbital planesinclined at 55 degreeswith the equator.
y This constellationprovides 5 to 8 SVsfrom any point on theearth.
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Paul Lammertsma
equator
orbital plane20,200 km
55
6 planes
Configuration
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Control segment:
y The control segmentcomprises of 5 stations.
y They measure thedistances of the overheadsatellites every 1.5 secondsand send the corrected
data to Master control.y Here the satellite orbit,
clock performance andhealth of the satellite aredetermined anddetermines whether
repositioning is required.y This information is sent to
the three uplink stations
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User Segment:y It consists of receivers that decode the signals from the
satellites.
y The receiver performs following tasks:y Selecting one or more satellites
y Acquiring GPS signals
y Measuring and tracking
y Recovering navigation data
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User Segment:y There are two services SPS and PPS
y The Standard Positioning Service
Each satellite transmits two l band frequencies L1 &L2 SPS- is position accuracy based on GPS measurements
on single L1 frequency C/A code
C/A ( coarse /acquisition or clear/access) does pseudo
random bi phase modulation on L1 freq
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User Segment:y The Precise Position Service
y PPS is the highest level of dynamic positioning based onthe dual freq P-code
y The P-code is a very long pseudo-random bi phasemodulation on the GPS carrier which does not repeat for267 days
y Only authorized users, this consists of SPS signal plus
th
e P code on L1 and L2 and carrier ph
ase measurementon L2
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The Broadcast
y Satellites broadcast over two reserved frequenciesy L1 frequency, at 1575.42 MHzy
L2 frequency, at 1227.6 MHzy L1 carries a C/A code, which can be identified by
civil receiversy L1 & L2 carry a P code, which can only be identified
by the U.S. military
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GPS Satellite Signal:y L1 freq. (1575.42 MHz) carries the SPS code and the
navigation message.
y
L2 freq. (1227.60 MHz) used to measureionosphere delays by PPS receivers
y 2 binary codes on L1 &L2 by the carrier phase arey The C/A code
y The P code
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How does the GPS work?y Requirements
y Triangulation from satellite
y
Distance measurement th
rough
travel time of radiosignals
y Very accurate timing required
y To measure distance ,the location of the satelliteshould also be known
y Finally delays have to be corrected
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PARTS OF GPS NETWORK
y GPS satellites.
y GPS ground support.
y GPS receivers.
Requirements
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Triangulationy Position is calculated
from distancemeasurement
y Mathematically weneed four satellitesbut three are
sufficient byrejecting theridiculous answer
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Pseudo range
Were exactly here
In two dimensions, this is the ideal situation
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Howitworks
The image cannot be displayed. Your computer may not have enough memory to open the image, or the imagemay have been corrupted. Restart your computer, and then open the file again. If the red x still appears, youmay have to delete the image and then insert it again.
The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may havebeen corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete theimage and then insert it again.
The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have beencorrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image andthen insert it again.
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Measuring Distancey Distance to a satellite is determined by measuring how
long a radio signal takes to reach us from the satellite
y
Assuming the satellite and receiver clocks are sync.The delay of the code in the receiver multiplied by thespeed of light gives us the distance
Distance = Time delay X Speed of light
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time difference
pseudo-randomcode generated
by GPS receiver
on the ground
pseudo-random
code generatedby GPS satellite
in space
The GPS receiver and satellite generate the same pseudo-random code at
exactly the same time. When the code arrives from the satellite, the time
difference is compared to the same code generated by the receiver. Thisdifference is multiplied by the speed of light (186,000 miles per second) to
determine the distance to the satellite.
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Getting Perfect timingy If the clocks are perfect sync the satellite range will
intersect at a single point.
y
But imperfect if the four satellite will not intersect atthe same point.
y The receiver looks for a common correction that willmake all the satellite intersect at the same point
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TypicalGPS Applicationsy Location - determining a basic position
y
Navigation - getting from one location to anoth
er
y Tracking - monitoring the movement of people andthings.
y Mapping - creating maps of the world
y Timing - bringing precise timing to the world
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Sublocations can have multiple
scales
Country level State level
City level
Campus level
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Errors
y Other objects exert gravitational force on each satellite
(e.g. sun, moon)y Effect of gravity is non-uniform during orbit.
y Radiation pressure (due to solar radiation).
y Atmospheric drag
y
Other effects
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Conclusion: Global Positioning Systems (GPS) give three-dimensional position, velocity and
time information to suitably equip users anywhere on or near the surface of the Earth
(and sometimes off the earth).
Global Navigation Satellite Systems (GNSS) are extended GPS systems, providing
users with sufficient accuracy and integrity information to be useable for critical
navigation applications.
By combining GPS with current and future computer mapping techniques, we will
be better able to identify and manage our natural resources.
Intelligent vehicle location and navigation systems will let us avoid congested
freeways and find more efficient routes to our destinations, saving millions of dollars in
gasoline and tons of air pollution.
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Web Sites:-
www. Garmin.com
www.cc.gatech.edu/ccg
www.ngs.noaa.gov/GPS/GPS.html www.seminars4u.com
www.wikipedia.org/wiki/gps
www.howstuffworks.com
www.gps.com
www.nemisis.in
Reference
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