Automatic location identification using a hybrid technique

Automatic location indication (ALI) has been mandated by the US Federal Communications Commission (FCC) for the use of Public Safety Answering Points (PSAPs) and other users, by late 2001. We analyze a hybrid approach which uses combination of time difference of arrival (TDOA) and independent time of arrival (TOA) information to supplement each other. Both pieces of information are available with no hardware modifications to currently-available handsets and relatively inexpensive alterations to the base station system. We obtain significantly reduced statistical errors compared with either technique separately. This reduction may be necessary for compliance with the FCC requirement. In addition, there is expected to be a reduction in the measurement bias. The technique has particular advantages in the large areas on the periphery of the central coverage regions