Cellular Telephone Positioning Using GPS Time Synchronization

Abstract

This paper presents a system to estimate the horizontal position of analog cellular telephones. Due to rules recently adopted by the FCC, cellular licensees must, by the year 2001, automatically provide the position of cellular 911 callers with an accuracy within 125 m in 67°/0 of all cases. The system presented herein estimates position using time difference of arrival for standard signals transmitted by cellular telephones to cell sites. Hyperbolic trilateration is performed using GPS receivers to time synchronize the cell sites. MUSIC, a superresolution estimation algorithm, is used to increase the resolution of the time of arrival estimate obtained via correlation. Simulations were performed based on the cellular cell site network of Telus Mobility in Calgary, Canada, and selected models of the mobile radio propagation channel. Multipath, a significant error source, was included in the channel model. According to the simulations the system as presented has an accuracy of approximately 90 m (670A). The presence of distant outliers was shown to be a function of the horizontal dilution of precision, a measure of the geometrical strength of a network for positioning purposes. System prototypes were field tested in four Telus Mobility cell sites. The results of these tests indicate an accuracy of 188 m (67%). When time averaging is used, the accuracy improves to 137 m (67’Yo). It is expected that accuracy will further improve when additional cell sites are used in the position estimation process.