How GPS Navigation Systems Work

Geo-Positioning Systems [GPS] are becoming an everyday personal and business electronics item. GPS relies on a US Defence satellite system.

In 1973 the U.S. Department of Defence launched the Navstar GPS network - a network of 24 satellites orbiting the earth every 12 hours and five ground stations.

This positioning system was made available for public use. With this capability, consumer location devices were produced to accurately determine location and other data such as current and average speed, directional heading, and elevation. These GPS devices need an unobstructed view of at least four satellites to provide a reliable 3D fix.

The GPS receiver overlays this location data onto map files stored on the unit, to give a current position on the map as well previous track. The receiver constantly recalculates position, giving real time position.

A typical GPS car navigation device contains:

• 12-channel receiver - the quality of the receiver determines how long it takes the device to acquire a 3D fix.
• Antenna to capture satellite signals - positioned to get a clear view of the sky.
• CPU to process the data and overlay on maps
• DVD Hard-drive - where maps on DVD's or available online are uploaded and stored. Some cheaper units do not upload the maps, but reference them off the DVD or CD.
• Display Screen - mostly color with handheld units using black and white
• Voice Interface - more advanced units

How The GPS Device Gets A Fix

The first time you start your GPS device, its data store is blank so needs a to collect satellite information to determine your position. This is known as a cold start. Some units only take 30 to 45 seconds to acquire a 3D fix during a cold start, while others can take several minutes. Subsequent position updates only take 3 to 4 seconds. If you go out of range from losing line of sight, such as passing behind a large building or through a tunnel, a good receiver will instantly recover, whereas weaker units will require more time to reacquire a 3D fix.

More on GPS Navigation Systems

• Comparing Onboard GPS Navigation Systems
• Comparing Portable GPS Navigation Systems
• Comparing Handheld GPS Navigation Systems
• GPS Navigation Mapping Media

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