How GPS Satellite Navigation works.

Global Positioning satellites are constantly circling the Earth (GPS stands for 'Global Positioning System'). Each follows a set path and speed around the globe and therefore, at any particular time, each satellite will be at a very precise location in the sky. Signals being constantly beamed to Earth from each satellite can be read by receiving equipment down below to very precisely position objects on the ground.

As long as the satellite receiver on the ground can read the position of at least three satellites, a process of mathematical triangulation allows it to calculate its own location. Portable SatNav devices generally rely entirely on GPS positioning technology along with sophisticated digital mapping.

The navigation device receives enough information from the satellites to provide a relatively accurate position on the ground, but digital mapping and some clever software is needed to synchronise the satellite signals and correct for slight errors. In this way, the SatNav device will show you on the road even if the satellite signals would have you motoring through the houses 30 feet to your right!

Some fixed In-Car Navigation systems will also include a gyroscope. This adds extra accuracy and becomes especially useful whenever satellite reception is impeded. The fixed systems also use a separate antenna that can be positioned for best reception. With the portable devices, it may be necessary to buy and mount an additional antenna if your vehicle has a heated or reflective windscreen.

The steps below outlines the process an in-vehicle GPS Satellite Navigation device, uses to provide live route-planning information.  There are now devices which also receive road traffic information transmissions and alter the route plan and journey time to compensate for for any delays caused by traffic congestion.

• Calculation of vehicle position Calculates the vehicle position (direction and current location) and creates a track

• Processing of the vehicle position data on the map Displays the current location and the track of the vehicle on the map

• Map Matching Compares the data of the current location and the track of the vehicle against the map data and aligns the vehicle position with the nearest road.

• GPS correction Aligns the vehicle position to the position plotted by the GPS.

• Distance correction Reduces (or corrects) the difference between the driving distance signals and distance data on the map

Construction of Car Navigation

The car navigation system consists of a Navigation ECU, display, GPS antenna and a remote controller. The example below illustrates the modules included in a navigation system with DVD mapping.

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GPS Explained

Circuit/ Packet switching