08-16-2017, 10:57 PM
GPS (Global Positioning System)
The global positioning system was developed by the United States Department of Defense. It uses from 24 to 32 satellites in medium-Earth Orbit that transmit precise microwave signals. This allows GPS receivers to determine their current location, time, and speed. GPS satellites are supported in the United States AIR FORCE.
GPS is often used by civilians as a navigation system. On the ground, any GPS receiver contains a computer that "triangles" its position on obtaining bearings from at least three satellites. The result is presented as a geographic position-longitude and latitude-to, for most listeners, with an accuracy of 10 to 100 metres. Applications can then use these coordinates to provide directions or pedestrian instructions.
Getting a lock on to GPS receivers on the ground, it usually takes some time, especially when the receiver is in a moving vehicle or in dense urban areas. The starting time for the GPS lock usually depends on how to start the GPS receiver. There are three types of start-hot, warm and cold.
Hot start, when the GPS device remembers your last calculated position and satellites in view, the Almanac is used (all satellites in the grouping), UTC Time and attempts to block the same satellites and calculate the new position on the basis of previous information. This is the quickest GPS lock, but it only works if you are usually in the same place as you were when the GPS was last turned off.
Warm start, when the GPS device remembers your last calculated position, Almanac and UTC time, but not which satellites are in view. Then it resets and tries to get the satellite signals and calculates the new position.
The receiver has a general idea of which satellites to look because he knows his latest position and Almanac data helps to determine which satellites are visible in the sky. It takes more time than a hot start, but not as long as the cold start.
And, finally,-cold start when the GPS device dumps all the information, trying to find the satellites, and then calculates a GPS lock. It takes more time, because there is no known information.
The GPS receiver must attempt to capture satellite signal from any of the available satellites, primarily as a survey that takes much longer than you know what to look for satellites. The GPS lock takes more time.
In an attempt to improve the time lock, mobile phone manufacturers and operators have Assisted GPS technology that loads the current ephemeris for several days in advance by means of wireless networks and helps the user position Triangulating cell towers, thus allowing the GPS receiver to get faster by several Castle (kilo) bytes.