Global 
The Global Positioning System (GPS) is a Global
Navigation Satellite System (GNSS) developed by the United States Department of
Defense. It is the only fully functional GNSS in the world. It uses a
constellation of between 24 and 32 Medium Earth Orbit satellites that transmit
precise microwave signals, which enable GPS receivers to determine their current
location, the time, and their velocity. Its official name is NAVSTAR GPS.
Although NAVSTAR is not an acronym, a few backronyms have been created for it.
The GPS satellite constellation is managed by the United States Air Force 50th
Space Wing. GPS is often used by civilians as a navigation system.
After
Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR's
prohibited airspace, President Ronald Reagan issued a directive making GPS
freely available for civilian use as a common good. Since then, GPS has become a
widely used aid to navigation worldwide, and a useful tool for map-making, land
surveying, commerce, scientific uses, and hobbies such as geocaching. Also, the
precise time reference is used in many applications including the scientific
study of earthquakes. GPS is also a required key synchronization resource of
cellular networks, such as the Qualcomm CDMA air interface used by many wireless
carriers in a multitude of countries.
The first satellite navigation system, Transit, used by the
United States Navy, was first successfully tested in 1960. Using a constellation
of five satellites, it could provide a navigational fix approximately once per
hour. In 1967, the U.S. Navy developed the Timation satellite which proved the
ability to place accurate clocks in space, a technology that GPS relies upon. In
the 1970s, the ground-based Omega Navigation System, based on signal phase
comparison, became the first worldwide radio navigation system. The design of
GPS is based partly on similar ground-based radio navigation systems, such as
LORAN and the Decca Navigator developed in the early 1940s, and used during
World War II. Additional inspiration for the GPS came when the Soviet Union
launched the first Sputnik in 1957. A team of U.S. scientists led by Dr. Richard
B. Kershner were monitoring Sputnik's radio transmissions. They discovered that,
because of the Doppler effect, the frequency of the signal being transmitted by
Sputnik was higher as the satellite approached, and lower as it continued away
from them. They realized that since they knew their exact location on the globe,
they could pinpoint where the satellite was along its orbit by measuring the
Doppler distortion.
from :wikipedia.org
The Global Positioning System (GPS) is a Global
Navigation Satellite System (GNSS) developed by the United States Department of
Defense. It is the only fully functional GNSS in the world. It uses a
constellation of between 24 and 32 Medium Earth Orbit satellites that transmit
precise microwave signals, which enable GPS receivers to determine their current
location, the time, and their velocity. Its official name is NAVSTAR GPS.
Although NAVSTAR is not an acronym, a few backronyms have been created for it.
The GPS satellite constellation is managed by the United States Air Force 50th
Space Wing. GPS is often used by civilians as a navigation system.
After
Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR's
prohibited airspace, President Ronald Reagan issued a directive making GPS
freely available for civilian use as a common good. Since then, GPS has become a
widely used aid to navigation worldwide, and a useful tool for map-making, land
surveying, commerce, scientific uses, and hobbies such as geocaching. Also, the
precise time reference is used in many applications including the scientific
study of earthquakes. GPS is also a required key synchronization resource of
cellular networks, such as the Qualcomm CDMA air interface used by many wireless
carriers in a multitude of countries.
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