The Global Positioning System (GPS) is a satellite-based navigation system that was developed by the U.S. Department of Defense (DoD) in the 1970s. Initially, it had only military application and was later made available to the public. Now, the system can be accessed by both civilians and the military.
GPS provides a continuous positioning and timing information anywhere in the world and under any weather conditions. GPS serves an unlimited number of users and is used for security reasons. GPS is a one-way passive system. The users can only receive the satellite signals.
GPS constists of a constellation of 24 satellites. The constellation (IOC) was completed in 1993. Only 4 satellites are needed to provide the positioning or location information. The GPS system was officially declared to have achieved FOC (full operational capability) in 1995, ensuring the availability of 24 fully functional satellites. The number of Satellites have been more then 24 since 1995.
GPS consistes of 3 segments:
- The space segment.
- The control segment.
- The user segment.
The space segment consists of the 24 constellation of satellites. Each GPS satellite transmits a signal which has a number of components:
- 2 sine waves (also known as the carrier frequency)
- 2 digital codes
- a navigation messagers
Introduction to GPS: the Global Positioning System (2002) by Ahmed El-Rabbany
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