Accuracy of iPhone Locations: A Comparison of Assisted GPS, WiFi and Cellular Positioning

The 3G iPhone was the first consumer device to provide a seamless integration of three positioning technologies: Assisted GPS (A-GPS), WiFi positioning and cellular network positioning. This study presents an evaluation of the accuracy of locations obtained using these three positioning modes on the 3G iPhone.The GPS technology adopted in most cell phones employs a server-side component
for the processing of the GPS signal and is referred to as Assisted GPS (A-GPS). While
high-sensitivity GPS chipsets have been adopted in recent years, A-GPS does not work
well indoors and as a result complementary positioning systems are employed under
these conditions.

Description of the positioning method behind the WiFi positioning system

Statements by Skyhook Wireless regarding the performance of its WiFi positioning

system

Most GPS-enabled cell phones, including the 3G iPhone, employ a technology known as Assisted GPS (A-GPS). With A-GPS many of the functions of a full GPS receiver are

performed by a remote GPS location server. This remote server provides the A-GPS
mobile device with satellite orbit and clock information; the initial position and time
estimate; satellite selection, range and range date; and position computation.