451 COMPUTER NETWORK GLOBAL POSITIONING SYSTEM GPS

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451 COMPUTER NETWORK GLOBAL POSITIONING SYSTEM
(GPS)

• DENIZ AKDEMIR
• DENIZ ICMELI
• ONUR YALMAN

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CONTENT

• What is GPS?
• History of GPS
• Why GPS?
• How GPS works?
• GPS elements
• Uses of GPS Technology
• GPS Competitors
• Future of GPS
• Conclusion
• References
• Questions

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WHAT is GPS?

• GPS, the Global Positioning System, is the only
  system today able to show you, your exact
  position on Earth at any time, any where, and in
  any weather. GPS refers to a group of U.S
  Department of defense satellites constantly
  circling the earth. The satellites transmit very
  low power radio signals allowing anyone with a
  GPS receiver to determine their location on earth.

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What Is GPS? (Contd)

• There are some satellites in space.
• The purposes which they are used for
• satellite TV,
• cellular phones,
• military purposes and etc.
• Satellites are also related with GPS.

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What Is GPS? (Contd)

• There are 24 satellites which surrounds the
  earth for GPS Operational Constellation. GPS
  satellites broadcast continuous navigation
  signals.

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History of GPS

• 1973
• It is decided to develop satellite navigation
  system based on the systems TRANSIT, TIMATION and
  621B of the U.S. Air Force and the U.S. Navy.
• 1978
• NAVSTAR (Navigation System with Timing And
  Ranging), now known as GPS (Global Positioning
  System), launched by U.S. Department of Defense
  for military use, with eleven satellites in orbit
  (1978  1985).
• 1979
• It is decided to expand the GPS system. After
  that, the resources are quite shortened and the
  program is restructured.
• 1982
• First GLONASS (Global Navigation Satellite
  System) satellites launched by the Russian
  Federation Ministry of Defense.
• 1983
• When a civilian airplane of the Korean Airline
  (Flight 007) was shot down by Soviet fighters
  after it had gone lost over Soviet territory, GPS
  was declassified by President Reagan. GPS moved
  from military effort to public project it was
  decided to allow the civilian use of the GPS
  system.
• 1989
• The first Block II satellite was installed and
  activated.

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History of GPS (Contd)

• 1990 1991
• Temporal deactivation of SA (Selective
  Availability) during the Gulf war. In this period
  civil receivers were used as not enough military
  receivers were available. On 1st July 1991 SA was
  activated again.
• 1994, March
• The last Block II satellite completes the
  satellite constellation.
• 1995, 17th July
• Full constellation of 24 GPS satellites in
  orbit. Full Operational Capability (FOC) is
  announced.
• 1996
• U.S. President Clinton authorizes SA (Selective
  Availability) to be phased out to provide
  civilians worldwide with greater GPS accuracy.
• 2000, 2nd May
• SA (Selective Availability) phased out as a
  result of the 1996 executive order by U.S.
  President Clinton. Civilians could now achieve
  10  15 meters accuracy, compared to the
  previously available 100 meters accuracy. This
  was a major win for the GPS consumers (and the
  GPS industry).
• 2004, 20th March
• Launch of the 50th GPS satellite.
• 2005, 25th September

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Why GPS?

• Determining Location
• Navigation
• Department of Defense needed worldwide
  positioning
• Tracking vehicles, and employees
• Get latitude, longitude and altitude with high
  degree of accuracy and little amount of skill

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How GPS Works?

• GPS receivers get signals from satellites then
  the user can see his position, velocity, time by
  the using gps device. Moreover, if needed,
  distance between selected points can be learned.
• GPS work in 5 steps
• Triangulation
• Measuring distance
• Getting perfect timing
• Satellites position
• Error correction

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Triangulation

• The basis of GPS
• Considers distance measurement by using three
  satellite that can point you in space.
• With an one satellite your possible circled
  position, which has a 20.000 km radius, is
  determined.
• By the help of the second satellite, your
  possible positions area narrowed.

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Triangulation (Contd)

• With the third satellite your possible two exact
  positions on the earth will be found by
  intersection of these satellites area, so a
  fourth measurement with another satellite will be
  needed but usually one point is ridiculous so
  you can learn your current position.

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Measuring distance

• You can measure your distance to the satellite by
  timing how long it takes for a signal sent from
  the satellite to arrive at your receiver.
• Timing is tricky
• Velocity x Time Distance this equation is
  used.
• Timed coded signals travel with the speed of
  light.
• Speed of light 299792.458 m/sec.

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Measuring distance (Contd)

• The difference in synchronous of the receiver
  time minus satellite time is the travel time.
• Pseudo random code (PRC) is used when the signals
  are sending.

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TIMING

• Satellites have atomic clock.
• To find the perfect timing an extra (fourth)
  satellite measurement is needed.

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Satellite Position

• According to the master plan of GPS, satellites
  have been placed into a precise orbit.
• Also all receivers have an almanac program to
  recognize where the satellite is in the space.
• To make things perfect, satellites are monitoring
  constantly by the ground stations to check their
  exact position, speed, altitude.
• By help of these checks, satellites find their
  destination.

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Satellite Position (Contd)
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Errors

• Speed of light is only constant on the
  experiments so when the signals are coming from
  satellite, their speed will slow down according
  to the environmental factors.
• By this way errors occurred.
• When the signal reaches to the ground, it may
  bounce off rough surfaces (Multipath error).
• Geometric dilution of precision (GDOP) principle
  is used to magnify other errors.
• The U.S. was very mindful of the fact that
  terrorists and unfriendly governments could use
  the accurate positioning provided by GPS and so
  intentionally degraded GPSs accuracy. This
  policy is called Selective Availability or SA.
  This involves the DOD introducing some "noise"
  into the satellite's clock data which, in turn,
  adds noise (or inaccuracy) into position
  calculations for encryption of the data. The DOD
  may also has been sending slightly erroneous
  orbital data to the satellites which they
  transmit back to receivers on the ground as part
  of a status message.

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Errors (Contd)
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GPS Elements

• GPS has three parts Space segment user segment
  and the control segment. The space segment
  consists of a constellation of 24 satellites and
  some spares, each in its own orbit which are
  20.000 kms above earth. The user segment consists
  of receivers, which you can hold in your hand or
  installed in a vehicle. The control segment
  consists of ground stations that make sure the
  satellites are working properly.
• A constellation of satellites
• Receivers
• Ground stations

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GPS Elements (Contd)
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A Constellation of Satellites

• GPS satellites each takes 12 hours to orbit
  earth. Each satellite includes an atomic clock.
  It is a very accurate device which keeps time
  within three nanoseconds to let it broadcast
  signals that are synchronized with those from
  other satellites. The signal travels to the
  ground at the speed of light. The difference
  between the time when the signal is received and
  the time when it was sent is multiplied by speed
  of light to calculate the distance to the
  satellite. In order to calculate the latitude,
  longitude and altitude, the receiver measures the
  distance to four separate GPS satellites.

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A Constellation of Satellites (Contd)

• GPS Satellites
• Name NAVSTARManufacturer Rockwell
  InternationalAltitude 20,200 kilometersWeight8
  60 kilograms (in orbit)Size5 meters with solar
  panels extendedOrbital Period 12 hoursOrbital
  Plane 55 degrees to equatorial planePlanned
  Lifespan 7.5 yearsCurrent constellation 24
  satellites Future satellites 21 developed by
  Martin Marietta.

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Receivers

• GPS receivers can be installed in your car or in
  an aircraft, submarine, truck or tank. Even you
  can hold it in your hand. These receivers detect,
  decode and process GPS satellite signals. There
  are more than 100 different receiver models on
  the world which are already in use. The newer
  models are now installed in cell phones.

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Receivers (Contd)
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Ground Stations

• There several ground stations which are located
  around the world.
• A master control station at Schriever Air Force
  Base in Colorado
• Five computerized monitor stations
• Hawaii and Kwajalein in Pacific Ocean
• Diego Garcia in Indian Ocean
• Ascension Island in the Atlantic Ocean
• Colorado Springs
• Four huge ground-antenna stations that send data
  and commands up to satellites and collect back
  from them

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Ground Stations (Contd)
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Uses of GPS Technology

• Location
• Navigation
• Tracking
• Mapping
• Timing

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GPS Competitors

• GLONASS
• GALILEO

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GLONASS

• GLONASS is the Russian Federation's satellite
  navigation system. It is very similar to GPS.
  There are 24 satellites in the constellation like
  GPS. The satellites are using two types of
  signals. One navigation signal is for civilian
  use and the other signal is reserved for Russian
  military use. There is a ground segment that
  monitors and controls the satellites. GLONASS is
  a more elegant and economical system design than
  GPS. Unfortunately there are a number of quality
  control issues and much more serious funding
  problems.

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GALILEO

• The Galileo satellite radio navigation system is
  launched by the European Union and the European
  Space Agency (ESA). The project architects plan
  deployment in 2006-7, becoming operational in
  2008 at a yearly cost of 220m. It is projected
  by 2008 a constellation of 30 satellites should
  be available.The technology behind Galileo is
  designed to be more accurate and more reliable
  than GPS or GLONASS. This will allow
  safety-critical systems - such as air traffic
  control, and ship and car navigation - to be run
  on the technology.

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Future Of GPS

• Remember when cell phones were the size of
  suitcases? What about when changing channels
  meant getting out of your sofa, walking over to
  the television across the room, and turning a
  knob until you found what you were looking for?
  The technology is advancing very fast. In the
  future we will locate any persons location in
  one or two seconds with our cell phones or very
  small receivers.

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Conclusion

• GPS is a very useful technology. It is widely
  evolved throughout the history. It is used in
  lots of branches in our lives and makes it more
  easier, safer and productive. The GPS has
  successfully accomplished in the sectors which
  are being used now. These successes leads GPS to
  develop continuously in the future. The number of
  users are increasing day by day.

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References

• www.gisdevelopment.net/tutorials/tuman004.htm
• www.scign.jpl.nasa.gov/learn/gps2.htm
• http//gpshome.ssc.nasa.gov
• www.humanitarianinfo.org/IMToolbox/03_Mapping_GIS_
  GPS/GPS/GPS_Reference/Gps4beginers.pdf
• www.gmat.unsw.edu.au/snap/gps/about_gps.htm
• www.palowireless.com/gps/tutorial.asp
• http//www.gpsfsinc.com/gps_facts.htm
• http//thoreau.dnr.state.mn.us/mis/gis/tools/arcvi
  ew/Training/WebHelp/Courses/GPS/GPSOverview/Page2.
  html
• http//www.novastars.com/gps/why.htm
• http//www.malima.com.br/gps/blog_commento.asp?blo
  g_id228
• http//users.ictp.it/radionet/ghana1998/GPS/PAGE1
  .HTM
• http//www.mapmiddleeast.org/magazine/2005/sep-oct
  /future_2.htm
• http//home.online.no/sigurdhu/GPS_history.htm

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Questions

• What is the distance between receiver and
  satellite if the delay time is 0.08 second?
• What is your opinion about the future of GPS
  different from the presentation?
• Is GPS will be a threat for human kind? (like
  government can track our private life etc.)

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• Thank You for your attention.....