A Pervasive Indoor-Outdoor Positioning System

Abstract

A new concept called Always Best Located (ABL) is introduced to achieve a pervasive indoor- outdoor positioning system. Designed as a combination of WLAN and GPS, this hybrid positioning system is shown to yield ubiquitous coverage and best-effort accuracy in any environment. An original mapping algorithm has been conceived to enable the system to discover the location of nearby WLAN access points on the fly, without requiring human intervention or connection to an existing database. Following an outline of positioning algorithms and location based application requirements, a comparative study of positioning technologies based on GPS, GSM, WLAN, and Bluetooth is presented. As revealed by this benchmark, none of the existing technologies suffice to provide ubiquitous coverage; however a combination GPS and WLAN is shown to provide excellent coverage and accuracy indoors as well as outdoors. New algorithms are then presented to illustrate how these two technologies can be combined to provide a continuous service by switching from one technology to another, to accurately locate the user indoors, and to automatically discover location of nearby WLAN access points. Finally the ABL system is validated over time by several users and is shown to yield 97% availability – the equivalent of more than 23 hours of service a day.