A Guide to Technology

Global Positioning system (commonly known as GPS) is a navigation and positioning tool.It was originally designed to defense soldiers to help them navigate in difficult terrains. Today GPS is used commonly for commercial and scientific purposes. Now a days it is also available in mobile hand sets for navigation

How does GPS work?
A GPS device receives signals from GPS satellites. A set of 24 such satellites orbit around earth with approximately 12 Hrs orbit cycles.
These satellites continuously send radio signals which are received by the GPS device. This GPS device does not transmit any signals back to the satellite.
Each GPS satellite transmits data that indicates its current location and the current time. All GPS satellites are synchronized and send signals at the same instant.
How is the position determined?
A GPS receiver knows the location of the satellite. This data is sent by the satellite. It also knows the time taken by the data to reach from satellite to the receiver. Thus it know the distance.
Now imagine an sphere whose center is the location of the satellite. The GPS device then lies on the surface of this sphere. If a GP receiver is receiving data from 3 or more satellites then the location of the receiver will be intersection of thee imaginary spheres which can be calculated easily.
The below figure shows the example.