How does GPS work?

In order for GPS tracking to work, it is necessary to have both access to the Global Positioning System and have a GPS receiver. The GPS receiver is able to receive signals that are transmitted by GPS satellites orbiting over head. Once these satellite transmissions are received by the GPS receiver, location and other information such as speed and direction can be calculated. A GPS receiver needs to receive transmissions from at least three or more GPS satellites to calculate its position effectively. GPS receivers usually measure the time delays between the transmission and reception of each of the satellites GPS radio signal. This technique of calculating distance using three separate transmissions is called trilateration.