The difference between standard GPS and A-GPS
June 25, 2007 by Don Smith
One of the big news in the new Nokia N95 firmware seems to be the added A-GPS (also known as assisted GPS) feature, which basically “is a technology that uses an assistance server to cut down the time needed to determine a location using GPS. It is useful in urban areas, when the user is located in ‘urban canyons’, under heavy tree cover, or even indoors.”
Yes it’s an ugly drawing but you get the picture huh?
What does this mean? Well a standard GPS like the one you have in your car, boat or even in your Nokia N95 (with todays firmware) need to synchronize with at least 3 satellites to calculate your position (yes it’s simple math; Pythagoras theorem anyone?). They also need a clear line-of-sight, which basically means no GPS positioning indoors, in tunnels and sometimes not even in your car (if your GPS device isn’t positioned very near a window). Assisted GPS devices are similar to fleet tracking systems because both use cell phone towers for receiving signals.
The Nokia A-GPS system uses an assistance server (Mobile Location Server) via your cellular network. The server either knows or learns the position of your closest cell phone tower and uses this to calculate your exact position. The server has more processor power than your cellphone/GPS and thus makes the calculations faster. The tower positions are also stored in a database for future use making everything work faster and smoother as the system learns new tower positions. This also enables you to use your GPS device indoors.