The Global Positioning System (GPS) is a satellite-based navigation system developed by the U.S. Department of Defense (DoD) in the early 1970s. Initially, GPS was developed as a military system to meet the needs of the U.S. military. However, it was later made available to the civilian sector and is now used as both a military and civilian system.
GPS provides continuous positioning and timing information anywhere in the world, regard less of weather conditions. For security reasons as well as because of its unlimited number of users, GPS is a unidirectional range finding (passive) system, which means that users can only receive satellite signals.
Global Positioning System nominally consists of a constellation of 24 operational satellites. This constellation, known as the Initial Operational Capability (IOC), was completed in July 1993. However, the official IOC announ cement was made on December 8, 1993.
To provide continuous coverage of the entire world, four Global Positioning System satellites were placed in each of six orbital planes. In this constellation geometry, 4 to 10 GPS satellites are visible anywhere in the world, considering an elevation angle of 10°. As mentioned earlier, only four satellites are needed to provide positioning (location) information.
About the Book
Introduction to GPS provides an up-to-date and easy-to-understand explanation of this very important technology without bogging the reader down in advanced mathematics. This edition contains a wealth of brand new content, including a chapter on Global Positioning System satellite orbits and new coverage of today’s hottest issues, such as accurate point positioning and location-based services.