Global positioning system

 Introduction
 The GPS satellite system
 Working of GPS
 Components of a GPS
 Applications
 Advantages and disadvantages
 Conclusion

 GPS was created and realised by US
department of defence(USDOD).
 GPS is a space-based global navigation
satellite(GNSS).
 Used for reliable location and time
information.
 It works in all weather conditions and all
times and day where on or near the earth.

 There is no subscription fee and setup
charges to use GPS.
 GPS is a useful tool for Commerce,Scientific
uses,Tracking and surveillance.

 GPS system is made up of a network of 24
satellites placed into the orbit by the US.
 It is placed 20,000 Km above the earth.
 Travelling speed is roughly 7,000 miles per
hour.
 It’s lifetime is about 10 years and the
replacement are constantly being built and
launched into the orbit.

 Satellite weight is about 2,000 pounds and it
is 17 feet across the solar panels extended.
 It is powered by solar panels.
 They also have back up batteries onboard to
keep them running even in solar eclipse
time,where there is no solar power.
 Small rocket boosters on each satellite keep
them flying in correct path(station keeping).

 The goal of GPS is to determine the User’s
position on earth in three dimensions:east-
west,north-south and vertical.
 GPS uses satellites and computers to
compute positions anywhere on earth.
 It is based on satellite ranging.
 Basic formula used in this process is
Distance=speed * Time.

Geometric Principle:
You can find one’s location if you know
its distance from other, already-known
locations.
Things which need to be determined:
 Time taken by the signals to reach the GPS
receiver.
 The Distance Between Receiver’s Position and
the GPS Satellites.

 SATELLITE RANGING – determining the
position on the earth by measuring the
distance from a group of satellites in space
to the receiver.
 To determine user’s position signals we use
four overhead satellites to determine it’s
position and the time of emission of the
signal.

GPS receivers store this orbit information
for all of the GPS satellites.
A GPS receiver can tell its own position
by using the position data of itself, and
compares that data with 3 or more GPS
satellite.
 By measuring the amount of time taken by
radio signal (the GPS signal) to travel from
the satellite to the receiver.

 GPS receiver has built in microprocessor to
display the location of the user.
 The user’s position is displayed on the unit’s
electronic map.

 Three major components of GPS are given
below.
 The control segment.
 The space segment.
 The user segment.

 The CS consists of following entities:
 Monitor Stations
 Ground Antennas
 Powered by solar cells.
 GPS satellites fly in circular orbits at an
altitude of 20,200 km.

 Falcon Air Force Base in Colorado.
 Cape Canaveral.
 Florida.
 Hawaii.
 Ascension Island in the Atlantic Ocean.
 Diego Garcia Atoll in the Indian Ocean.
 Kwajalein Island in the South Pacific Ocean.

 Ground antennas monitor and
Track the satellites from
horizon to horizon.
 They also transmit correction information to
individual satellites.
 Communicate with the GPS satellites for
command and control purposes.

 The space segment is composed of 24 to 32
satellites in MEO.
 Contains payload adaptors to the boosters
required to launch them into the orbit.

 GPS receivers are generally
Composed of
1.An antenna( tuned to the frequencies
transmitted by the satellites),
2.Receiver-processors, and
3.Highly-stable clock( commonly a crystal
oscillator).
 They can also include a display for showing
location and speed information to the user.

 Surveying : Surveyors use
absolute locations to make
maps and determine
boundaries.
 Missile and Propulsion
guidance.

 Tectonics:GPS enables direct fault motion
measurements in earth quakes.
 Navigation.
 Target tracking.
 Missile guidance.
 Search and rescue.
 Remote sensing.

 Materials used to manufacture GPS are
affordable.
 GPS can provide worldwide, three-
dimensional positions, 24 hours a day, in any
type of weather.
 It uses one way transmission,hence GPS
transmitter is not needed.
 Size is small.

 There must be a relatively clear "line of
sight" between the GPS antenna and four or
more satellites.
 Difficulties may occur while tracking in urban
areas.
 The GPS constellation, like manmade stars in
the sky, can be used for guiding and
navigation.

Global positioning system

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