Time Difference of Arrival
The positioning method known as uplink time of arrival (TOA) is based on the time of arrival of a known signal sent from the mobile device and received by three or more base stations (see Figure 5.9). The signal is the access burst created by having a mobile device perform an asynchronous handover.
Figure 5.9. TDOA.
The TDOA values are calculated by pairwise subtracting the TOA values at the SMLC. The position of the mobile device is then calculated by hyperbolic trilateration (see the earlier section “How GPS Works”), provided that the geographic coordinates of the measurement units are known and the timing offset between ...