A-GPS (Assisted-Global Positioning System) 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 9-1-1 requirement to make cell phone location data available to emergency call dispatchers.