How a GPS Unit Works

Identification

Global positioning system (GPS) is a technology that utilizes radio waves, satellites and various types of receivers to track a specific location. GPS units come in pocket-sized handheld models, or ones designed to function as a navigation system in a car. The original idea was developed by the United States military as a satellite network for navigation.

A GPS unit works off of a network of 27 satellites that orbit the Earth, 24 hours a day. These satellites are solar-powered machines that move in coordinated patterns so that a minimum of four satellites are accessible from any one location. A clear view of the sky is necessary for a GPS unit to work.

Function

GPS units work off of radio waves that travel between the satellites. These waves are used by the satellites to determine the unit's exact location. The unit itself "calls out" to four nearby satellites, which is how they know to start tracking. The satellites then work to locate the unit through a process called trilateration, which involves the satellites working together to determine the distance between the unit and each satellite, and making calculations from there. All of this is accomplished using radio waves.

The distance between the devices is calculated based on the amount of time it takes for the satellites' signals to reach the receiver. In order to do this, both the receiver and the satellites work off synchronized, digital time patterns that enable a GPS unit to approximate a nearby satellite's location. Distance can then be calculated based on how long it takes the satellite's signal to reach the unit.

Differential GPS

As innovative as GPS technology may be, it's not without its flaws. Global positioning systems rely on radio waves being able to travel through the atmosphere unimpeded, but the Earth's atmosphere can actually slow down radio wave speeds. Random obstructions like tall buildings can also cause problems in terms of how accurate the communications between a satellite and unit will be. Any signal delays between the two devices will throw off directional bearings, causing inaccurate information to be relayed to the GPS unit.

Differential GPS is a system designed to correct any possible errors that may occur. This system uses an added ground-based station that acts as an intermediary between satellite transmissions and local GPS units. This system works because ground stations already know their own locations, which makes it easier for them to calculate signal differences coming from satellites. These stations, in effect, relay any corrections to GPS units within the area that are equipped to receive differential signals.

Resources

• Check out car GPS reviews.
• Read more about GPS at Consumer Reports.