There are various methods for determining the position of mobile devices in mobile networks, several of which are based on the measurement oftransit times or difference times. These include Time of Arrival (ToA) and Time Difference of Arrival( TDoA), Observed Time Difference of Arrival( OTDoA) and their various variants.
Time of Arrival is about the differences in the propagation times of an exactly synchronous signal transmitted by at least three base stations. The transmitting stations are the base stations, and the receiving station is the mobile device, cell phone or smartphone. The exact synchronous signal can be a timestamp sent by all base stations at the exact same time, or Timing Advance( TA), a distance-dependent radio signal.
Different distances between the base stations and the mobile device ensure that the three time stamps are received by the receiving device with a small time offset. The distances are proportional to the signal propagation times. From these and the known signal propagation speed, the distance to the three base stations can be calculated and, using their geographic coordinates, the geographic position of the mobile station.