Locating mobile phones and the US wireless E-911 mandate

The first commercial cellular phone systems were deployed in the early 1980s. Since that time there has been an almost global revolution in the development of wireless communications products. By contrast, the means to actually locate wireless transmitters has been available for decades. Dominated by defence applications, the benefits of applying this technology in the cellular world have only just begun to be realised. This is particularly so in the US, where the Federal Communications Commission (FCC) has mandated that cellular and PCS carriers must be able to locate mobile phones making emergency 911 calls with an accuracy of better than 125 m RMS by October 2001. KSI, a US based company, have been developing the means to locate mobile phones in an emergency since 1986. Based upon years of localisation and tracking experience in defence related work, the basic technology exploits angle-of-arrival (AOA) techniques. Back in 1991, KSI were the first to deploy a system (comprising two sites) that could locate and track an analogue AMPS phone. Currently, KSI have a four-site system that is capable of locating both analogue AMPS and digital TDMA (IS-136) phones. A larger scale field trial is planned for later this year. This article describes KSI's technology and provides a sample of the current field trial results. Preliminary data indicates an accuracy of better than 70 m RMS.