<P> Assisted GPS or Augmented GPS (abbreviated generally as A-GPS and less commonly as aGPS) is a system that often significantly improves the startup performance--i.e., time - to - first - fix (TTFF)--of a GPS satellite - based positioning system . A-GPS is extensively used with GPS - capable cellular phones, as its development was accelerated by the U.S. FCC's 911 requirement to make cell phone location data available to emergency call dispatchers . </P> <P> Standalone / self - ruling GPS devices depend solely on information from satellites . A-GPS augments that by using cell tower data to enhance quality and precision when in poor satellite signal conditions . In exceptionally poor signal conditions, for example in urban areas, satellite signals may exhibit multipath propagation where signals skip off structures, or are weakened by meteorological conditions or tree canopy . Some standalone GPS navigators used in poor conditions can't fix a position because of satellite signal fracture and must wait for better satellite reception . A regular GPS unit may need as long as 12.5 minutes (the time needed to download the GPS almanac and ephemerides) to resolve the problem and be able to provide a correct location . </P> <P> An assisted GPS system can address these problems by using external data . Utilizing this system can come at a cost to the user . For billing purposes, network providers often count this as a data access, which can cost money, depending on the plan . </P>

What is the difference between gps and a gps
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