GPS, or Global Positioning System receivers has become quite an ordinary gadget found in many new models of cars today. There are also some portable hand-held models in use that help people find their location any where on the planet, depending on the features provided by a certain GPS receiver. The GPS receiver has become an effective gadget that helps people find their way and avoid getting lost.

GPS receivers work well in helping people find their way with the use of a constellation of 27 satellites orbiting the Earth. 24 of these satellites are always in operation with the extra three always on standby in case one fails. The system was primarily developed and used by the US military as an aid for their military navigation systems. It was eventually opened for civilian use later on. It was during this time that the GPS receivers came into common use among more and more people.

The earth orbiting satellites of the GPS are 3,000 to 4,000 pound man-made machines that circle the earth at around 12,000 miles above the surface. These solar-powered satellites make two complete rotations daily and with their orbits specially designed so that at least four of these satellites are visible on any point on earth at any one time. The satellites are also equipped with transmitters that send various data to GPS receivers on earth.

The job of a GPS receiver is to locate four or more satellites and take their data transmission. The data taken from the different visible satellites by the GPS receiver are used to figure out the location and the distances of the satellites to one another and deduce the receiver's own location. This process is based on a simple mathematical principle known as trilateration. The principle uses the known location of three or more reference points and then the measurement of the distance between a central point to each reference point.

The GPS receiver calculates the distance from GPS satellites by measuring how long it takes for the signal to get from the satellite to the receiver. At a particular time, the satellite transmits a long digital pattern which the receiver also begins running at exactly the same particular time. When the satellite's signal reaches the GPS receiver, its transmission pattern will be a bit behind the time the receiver plays the similar pattern. The difference between them is equal to the signal's travel time. The GPS receiver then determines how far the signal has traveled to get the distance of the satellite.

For the system to work, the receiver and the satellite must work under a synchronized system of clocks that is accurate down to the nanosecond. The GPS receiver must also have to know where the satellites actually are in their orbits at any particular time. In order to do this, GPS receivers have an almanac of satellite movements stored in the that tells them where each satellite should be at any given time.