Location Tracking using Differential Range Measurments

G. Edwards and R. Jayne

Keywords

Location technique, E911 solution, geolocation in cellular communication, and position location

Abstract

Automatic vehicle location and automatic vehicle monitoring systems were developed originally to track fleet vehicles such as bus lines, truck lines, taxicabs, police patrol cars, and delivery vehicles. In a bus system, individuals known as "point men" were situated at certain places in the bus route to monitor the flow. In police work, a jurisdiction was subdivided into sectors to help dispatchers identify patrol vehicles in particular geographic areas. The widespread acceptance of wireless cellular and personal communication systems by the public has lead to an exponential growth in the industry. Each mobile telephone or pager is connected electronically to a fix radio infrastructure, which provides an opportunity for applying an automatic monitoring system. Thus, the potential and opportunity to automatically track a mobile station are unlimited. A major driving force behind geolocation tracking is emergency calls, E-911. A large number of emergency calls are place from mobile telephones, so it is important that one is able to achieve a position fix on these calls. Thus, there is a need to develop accurate and efficient algorithms for locating a mobile user. In this article we propose an algorithm using differential range measurements to determine a mobile’s location. A differential range measurement is defined as the difference between two range measurements. A closed-form location algorithm based on the least-squares solution was developed. This estimation algorithm was shown to be tolerant to measurement errors caused by unsynchronized base station clocks.

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