A Software System for Locating Mobile Users: Design, Evaluation, and Lessons

Abstract

We have built a software system, RADAR, to locate mobile users connected to an in-building radiofrequency (RF) wireless LAN. RADAR uses signal strength information extracted from the wireless network interface, in conjunction with a Radio Map of the building, to determine location. Over the past year we have deployed this system in multiple buildings on our campus using two different wireless LAN technologies and two widely used operating systems. This experience has led us to identify some shortcomings of the basic RADAR system and fundamental limitations in the way wireless network hardware is abstracted in contemporary operating systems. To address the shortcomings, we present several novel algorithms, including an environmental profiling algorithm to compensate for the vagaries of the RF environment, and a history-based algorithm for continuous user tracking. Performance evaluation of these algorithms using extensive data collected from our deployments shows that the accuracy of p...