How does Global Positioning System (GPS) work?
What is GPS?
The global positioning system is a space based satellite navigation system which provides reliable and accurate location and time information in any weather at all times anywhere on or near to earth where an unobstructed line of site is available to four or more GPS satellites. The United States military developed and implemented this system of satellite network as military navigation system but soon opened it to public use. Anyone with appropriate receiver can freely access the GPS network .
How does it work?
The global positioning system consist of a network of 27 solar powered satellites orbiting around the earth. among these satellite 24 are in operation and the rest is kept as backup in case of failure. Each of these circle the globe at about 19000 km, making two complete rotations every day. The orbits are so arranged that at any time anywhere on the earth at least four satellites are visible in the sky. A GPS receiver must be locked on to atleast three satellites to calculate 2d position (longitude and latitude) and track movement. If four or more satellites are in view the receiver can calculate 3d view (latitude, longitude and altitude). once the device determines the user position, it can further calculate distance to destination, sunrise and sunset, trip distance, track, speed, bearing and more.
How does it determine position?
GPS satellites transmit data containing their location and time. the receiver receives signals from different satellites at a slightly different time, because some satellites are further away than others. The distance can be calculated by estimating the amount of time the signal it takes to reach the receiver.This process of determining position is known as trilateration. In this process each receiver is located on the surface of an imaginary sphere centered at the satellite. By determining the size of several spheres one for each satellite, the receiver can be located at the intersection point of spheres. Most GPS receivers now can locate the position with 10 meter accuracy.
What is the frequency of Gps transmission?
Civilian receivers use a signal frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight and they can pass through clouds, plastic, glass etc.. but cant penetrate solid objects like buildings and mountains.