gps (global positioning system)

GROUP MEMBERS Tahir Ilyas 01121005&Iqra Hamid 01121004Submitted to:

Sir Abdul MalikDepartment of Electronics

University of Lahore

G LOBALPS

OSITIONINGYSTEM

WHAT IS GPS?• Satellite based

navigation system.• Based on a

constellation of about 24 satellites

• Developed by the United States Department of Defense (DOD)

WHAT IS GPS?

• Can provide accurate positioning 24 hours a day, anywhere in the world.

• No subscription fees or setup charges to use GPS.

• GPS satellites also called NAVSTAR, the official U.S. DOD name for GPS

STRUCTURE

Space Segment Control Segment

User Segment

STRUCTURE SPACE SEGMENT:

• GPS Satellite constellation composed of 24 operational satellites in space.

• These 24 satellites are placed in 6 circular orbits of period equal to 12hrs and these orbits are equally spaced with 60 degrees apart and at an inclination angle of 55 degrees to equator

STRUCTURE CONTROL SEGMENT:• The control segment comprises of 5 ground stations

located on equator.(4-monitor and 1-master station)• Monitor stations measure the distances of the

overhead satellites every 1.5 seconds and send the corrected data to Master station.

• In Master station the satellite orbit, clock performance and health of the satellite are determined and determines whether repositioning is required.

• This information is sent back to the satellites using ground antennas.

Control Segment

Space Segment

User Segment

Monitor Stations

GroundAntennas

Master Station

STRUCTURE

STRUCTURE USER SEGMENT:

• The User Segment consists of all earth-based GPS receivers.

• The user segment is totally user community, both civilian and military.

HOW GPS DETERMINES A LOCATION

HOW GPS DETERMINES A LOCATIONThings which need to be determined: • Current Locations of GPS Satellites• The Distance Between Receiver’s Position and the GPS

Satellites

CURRENT LOCATIONS OF GPS SATELLITES

• GPS satellites are orbiting the earth at an altitude of 11,000 miles.

• The orbits, and the locations of the satellites, are known in advance.

• GPS receivers store this orbit information for all of the GPS satellites in an ALMANAC*.

* THE ALMANAC IS A FILE WHICH CONTAINS POSITIONAL INFORMATION FOR ALL OF THE GPS SATELLITES

• All 24 satellites are divided into 6 parts.

• There are 4 satellites in each part.

• A definite orbit is defined for each part.

• Each of these 3,000- to 4,000-pound solar-powered satellites.

DISTANCE BETWEEN RECEIVER’S POSITION & THE GPS SATELLITES• By measuring the amount of time taken by

radio signal (the GPS signal) to travel from the satellite to the receiver.

• Radio waves travel at the speed of light, i.e. about 186,000 miles per second.

• The distance from the satellite to the receiver can be determined by the formula “distance = speed x time”.

GPS ERROR BUDGETDifferent errors can cause a deviation of +/- 50 -100 meters from the actual GPS receiver position which are :

ATMOSPHERIC CONDITIONS:

• Speed of GPS signal is affected by ionosphere & troposphere.

• Which cause a deviation of 0 to 30 m. from the actual position of receiver.

EPHEMERIS ERRORS:

• The predicted changes in the orbit of a satellite.

• Which cause a deviation of 0 to 5 m. from the actual position of receiver

CLOCK DRIFT:

• Due to different code generations in satellite and receiver simultaneously.

• Which cause a deviation of 0 to 1.5 m. from the actual position of receiver

MULTIPATH:

• Bouncing of GPS signal due to a reflecting surface before reaching to receiver antenna.

• Which cause a deviation of 0 to 1 m. from the actual position of receiver

MEASURING GPS ACCURACY

The geometry of the constellation is evaluated by Dilution Of Precision, or DOP.

DOP

INCREASING ACCURACY OF GPS

• Differential correction provides accuracy within 1-5 m.

• Coarse Acquisition receiver provides accuracy within 1-5m.

• Carrier Phase receivers provides accuracy within 10-30 cm.

• Dual-Frequency receivers are capable of providing sub-centimeter GPS position accuracy.

GPS SIGNALS

• Coarse/Acquisition code.• Precision code.• Navigation message.• Almanac.• Data updates.

GPS FREQUINCIES

• L1 (1575.42 MHz)• L2 (1227.60 MHz) • L3 (1381.05 MHz)• L4 (1379.913 MHz)• L5 (1176.45 MHz)

FREQUENCY INFORMATION

• The C/A code is transmitted on the L1 frequency.• The Precision-code is transmitted on both the L1 and L2

frequencies.• L3 is used by the Defense Support Program to signal

detection of missile launches, nuclear detonations, and other applications.

• L4 is used for additional correction to the part of the atmosphere that is ionized by solar radiation.

• L5 is used as a civilian safety-of-life signal.

ADVANTAGES OF GPS• GPS is extremely easy to navigate as it tells you to the

direction for each turns you take or you have to take to reach to your destination.

• GPS works in all weather so you need not to worry of the climate as in other navigating systems.

• The GPS costs you very low. • The most attractive feature of this system is its100%

coverage on the planet. • It also helps you to search the nearby restaurants, hotels

and gas stations and is very useful for a new place. • Due to its low cost, it is very easy to integrate into other

technologies like cell phone.

DISADVANTAGES OF GPS• GPS satellite signals are weak, so it doesn't work as well

indoors, underwater, under trees, etc. • The highest accuracy requires line-of-sight from the

receiver to the satellite, this is why GPS doesn't work very well in an urban environment.

• The US DoD (dept. of defence) can, at any time, deny users use of the system (i.e. they degrade/shut down the satellites).

• If you are using GPS on a battery operated device, there may be a battery failure and you may need a external power supply which is not always possible.

APPLICATIONS

AVIATION AGRICULTURE

MARINE TIMING

SPACE RAILWAYS

ROADWAYS DISASTER RELIEF

Name Launch DateNAVSTAR 64 (USA 206) August 17, 2009

NAVSTAR 63 (USA 203) March 24, 2009


NAVSTAR 61 (USA 199) December 20, 2007

NAVSTAR 60 (USA 196) October 17, 2007

NAVSTAR 59 (USA 192) November 17, 2006

NAVSTAR 58 (USA 190) September 25, 2006



NAVSTAR 55 (USA 178) June 23, 2004


NAVSTAR 53 (USA 175) December 21, 2003


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http://www.n2yo.com/satellite/?s=35752

http://www.n2yo.com/browse/?y=2009&m=8

























Name Launch DateNAVSTAR 51 (USA 166) January 29, 2003

NAVSTAR 50 (USA 156) January 30, 2001


NAVSTAR 48 (USA 151) July 16, 2000

NAVSTAR 47 (USA 150) May 11, 2000

NAVSTAR 46 (USA 145) October 7, 1999







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gps (global positioning system)

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