Assisted GPS, also known as A-GPS or AGPS, enhances the performance of standard GPS in devices connected to the cellular network. A-GPS improves the location performance of cell phones (and other connected devices) in two ways:
-By helping obtain a faster "time to first fix" (TTFF). A-GPS acquires and stores information about the location of satellites via the cellular network (see almanac) so the information does not need to be downloaded via satellite.
-By helping position a phone or mobile device when GPS signals are weak or not available. GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. A-GPS uses proximity to cellular towers to calculate position when GPS signals are not available.