Gps Handouts

GLOBAL POSITIONING SYSTEM (GPS) Cena, Patrick

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Matienzo, Rheamel  ______ is a satellite based based navigation navigation system. system.     

Based on a constellation of about 24 satellites Developed by the United States Department of Defense (DOD) 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

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1993  –   24th satellite launch; initial operational capability 1995  –   full operational capability (cost of 12 Billion US taxpayer Dollars) May 2000  –   Military accuracy available to all users  ________________  ________________  –   successful tests of Assisted GPS for mobile phones  ________  –   1st modernized GPS satellite was launched and Began transmitting a second civilian signal for enhanced user performance

Structure of GPS  ___________________   ___________________ - (SS) is composed of the orbiting GPS satellites, or Space Vehicles (SV) in GPS parlance. The GPS design originally called for 24 SVs, eight each in three approximately circular orbits, but this was modified to six orbital planes with four satellites each. The six orbit planes have approximately ______ inclination (tilt relative to the Earth's equator) and are separated by  ______ right ascension ascension of the ascending ascending node (angle along the equator from a reference point to the orbit's intersection). intersection).  The control segment is segment is composed of:

Early Solutions 

Marking trails with piles of stones (problems when snow falls or on ocean )  Navigating by STARS (requires clear nights and careful measurements)  Most widely used for centuries Modern Ideas Sonar: uses the echo principle by sending out sound waves underwater or through the human body to locate objects. Radar: uses radio waves, which are a type of electromagnetic energy to locate objects. History of GPS 

Developed by US Department of Defense  Defense Navigation Satellite System  1969 –  Defense (DNSS) formed  1973  –   ___________ Global Positioning System Developed  first 4 satellites launched  1978 –  first

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a master control station (MCS), an alternate master control station, four dedicated ground antennas, and  _____ dedicated dedicated monitor monitor stations. stations.

User segmentsegment- segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service, and tens of millions of civil, commercial and scientific users of the Standard Positioning Service. In general, GPS receivers are composed of an  ___________, tuned tuned to the frequencies frequencies transmitted by the satellites, receiverprocessors, and a highly stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user. A receiver is often described by its number of channels: this signifies how many satellites it can monitor simultaneously. Originally limited to four or five, this has progressively increased over

the years so that, as of 2007, receivers typically have between 12 and 20 channels.

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How GPS determine LOCATIONS THINGS NEEDED TO BE DETERMINED :

Current Locations of GPS Satellites  The Distance between the receiver and the GPS satellites

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TRILATERATIONS

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In geometry, ______________ is the process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles.

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Current Locations of GPS Satellites 

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GPS satellites are orbiting the earth at an altitude of ________________.  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 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 3,000-4,000-pound solarpowered satellites

Distance between the and the GPS satellite 

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receivers’  

Atmospheric Conditions:  Speed of GPS signal is affected by ionosphere & troposphere  Which cause a deviation of 0  –  30 meters from the actural position of receiver  ___________________:   The predicted changes in the orbit of a satellite  Which cause a deviation of 0  –  5 meters from the actual position of receiver Clock drift  Due to different code generations in satellite and receiver simultaneously  Which cause a deviation of 0  –   1.5 meters from the actual position of receiver  ______________  Bouncing of GPS signal due to a reflecting surface before reaching to receiver antenna  Which cause a deviation of 0  –  1 meters from the actual position of receiver

Position

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 _________________________.  The distance from the satellite to the receiver can be determined by the formula “Distance = SPEED x TIME”

GPS error budget Different errors can cause a deviation of ±50100 meters from the actual GPS receiver position which are:

Measuring GPS accuracy 

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

Increasing the Accuracy of GPS 

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 ____________________________   –   provides accuracy within 1- 5 m COARSE ACQUISITION RECEIVER  –  provides accuracy within 1 - 5 m CARRIER PHASE RECEIVERS - provides accuracy within __________ DUAL FREQUENCY RECEIVERS  –   are capable of providing sub-centimeter GPS position accuracy

GPS FREQUENCY

FREQUENCY INFOs 

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 The C/A code is transmitted on the L1 frequency as a _________ signal  The ___________ is transmitted on both the L1 and L2 frequencies as a 10.23MHZ signal L3 is used by the Defense Support Program to signal detection of missile launches, nuclear detonations, and other applications  ____ is used for additional correction to the part of the atmosphere that is ionized by the solar radiation L5 is used as a civilian safety-of-life (SoL) signal

Applications of GPS         

Aviation Agriculture Marine  Timing Space Railways Roadways Disaster relief Mobile games

GPS Operational Satellites

GPS drawbacks   

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Signal Multipath Atmospheric Effect No GPS Signal in o Indoor o Underwater o Underground Attacks