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