subject: The Difference between GPS and A-GPS [print this page] The Difference between GPS and A-GPS The Difference between GPS and A-GPS
A couple of days ago, a customer asked me what A-GPS meant because he saw a cell phone's description says to have A-GPS. Well, I guess plenty people may also feel confused about the two conceptions, so I'm going to explain them here.
GPS (Global Position System), as most people know, was a technology developed by the military to provide an edge in the battlefield. The GPS device receives information from any four of the 32 satellites that orbit the earth. It then calculates the distances from the satellites and derives its location by trilateration.
According to Wikipedia, A-GPS (Assisted GPS) is "a system which can, under certain conditions, improve the startup performance, or TTFF (Time To First Fix) of a GPS satellite-based positioning system. It is used extensively with GPS-capablecell phones as its development was accelerated by the U.S. FCC's 911 mandate making the location of a cell phone available to emergency call dispatchers".
A standard GPS needs to synchronize with at least 3 satellites to calculate your position. A-GPS are common on mobile phones where the data link is already in place. The information from the assistance server can allow the device to provide the correct location where a standalone GPS receiver would otherwise no work. A-GPS is also able to arrive to a fix much faster compared to GPS, especially the first time the device is booted. These desirable features make A-GPS somewhat superior to GPS in terms of performance.
Take this 3.6-inch Capacitive Touch-screen GSM/CDMA Dual SIM Cell Phone as an example. Its A-GPS system uses your mobile location server as an assisted server via your cell phone network. The server would learn the position of your closest cell phone tower and uses this to calculate your exact position. It has more processor power than your cell phone/GPS and thus makes the calculations faster. The tower positions would also be stored in a database for future use to make everything work faster and smoother when the system learns new tower positions. This also enables you to use your GPS device indoors.
Take this 3.6-inch Capacitive Touch-screen GSM/CDMA Dual SIM Cell Phone as an example. Its A-GPS system uses your mobile location server as an assisted server via your cell phone network. The server would learn the position of your closest cell phone tower and uses this to calculate your exact position. It has more processor power than your cell phone/GPS and thus makes the calculations faster. The tower positions would also be stored in a database for future use to make everything work faster and smoother when the system learns new tower positions. This also enables you to use your GPS device indoors.
