A system to estimate the horizontal position of cellular telephones operating in the Advanced Mobile Phone Service is developed and its performance evaluated. This system, named Cellocate™, was designed and developed for the application of automatic location of cellular 911 callers. Cellocate™ implements a superresolution based algorithm to estimate, at a number of cell sites, the time of arrival of signals transmitted by a cellular telephone. The time of arrivals are differenced between the cell sites and hyperbolic trilateration is used to estimate the position of the cellular telephone. Time synchronization between the various cell sites is implemented through the use of a GPS receiver, operating in time transfer mode, at each cell site. Least squares is used in the position estimation process to make redundant observations consistent.

The performance of Cellocate™ is evaluated though the use of simulations and field tests. The simulations indicate that for an actual cellular network in Calgary, Alberta, and for typical propagation losses and multipath effects, Cellocate™ is able to estimate the horizontal position of a cellular telephone with an accuracy of 119 m (67%). Operational field tests, in which the Cellocate™ system was installed in four working cell sites, indicate a positioning accuracy between 189 m and 287 m (67%). Positioning accuracy is shown to be a function of received signal SNR, multipath, geometry, and calibration of the system biases. Significant improvement in the precision of the position estimates is achieved by averaging of the results. Given proper system calibration, as well as adequate geometry and signal strength, Cellocate™ will meet the Federal Communications Commission requirement of 125 m (67%) for automatic 911 caller location.