01-04-2011, 12:49 PM
Presented by:
Chandraraj Naidu L
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Brief History Evolution of the GPS
First Satellite Navigation Systems
• Transit
• Timation
Ground based system Omega
DNSS, Navstar-GPS
Military and Civilian Usage policies
Selective Availability and its deactivation
Free Availability across the world
Nearly 60 satellites so far into space
33 currently in orbit
Global Navigation Satellite System
Autonomous geo-spatial positioning with global coverage
Allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few meters
Receivers calculate the precise time as well as position
Precision in the delivery of weapons to targets
Troops can be directed and locate themselves easily
US GPS and Russian GLONASS only two fully operational GNSS
Upcoming GNSS:
European Union – Galileo (by 2014)
China – Compass (by 2020)
Global coverage achieved by constellation of 20–30 Medium Earth Orbit satellites on several orbital planes
Operator of a GNSS has the ability to degrade / eliminate services over any territory it desires
Classification:
GNSS-I
GNSS-II
Regional Systems
GNSS Augmentation Systems
GNSS Basic Components
Satellite constellation in space
Satellite control unit on Earth
Receiver unit with the user
Global Positioning System
Basic Concept
Receiver calculates own position with respect to at least 3 satellites
Satellites provide continually updated almanac
Satellite continually transmits messages that include
The time the message was transmitted
Precise orbital information (the ephemeris)
The general system health & orbits of all GPS satellites
Trilateration used to compute distance
Final position in terms of latitude, longitude and altitude
Devices can derive direction and speed information
Data can be processed to be placed on a pre-loaded map
Minimum of 4 satellites used for accurate computations
Global Positioning System
Structure
Three major segments
Space Segment
Control Segment
User Segment
Space Segment
27 to 32 satellites in medium Earth orbit
6 planes with 4 satellites each
Approx. altitude 20,000 km
Additional satellites improve precision of GPS calculations
Constellation in non-uniform arrangement
Improves reliability and availability