June 01, 2004 | Kolodziej, Kris
IMAGINE THAT YOU NEED TO MAKE AN EMERGENCY CALL FROM A mobile phone inside a building that's on fire. You're disoriented by the smoke around you and are unable to describe your location to rescue personnel. By calculating the signal's time and distance to nearby cell-phone towers, mobile networks can calculate a position but the accuracy is rather low (50-300 meters).
It's also possible that a mobile phone (if it's on the top floors of a tall building) can be connected to a transmitter in a neighboring cell, causing the accuracy to go down to kilometers. Calls from mobile phones in multi-story buildings provide information that will, at best, identity a few buildings or the block that the call originated, but rescue teams need more-detailed information to find emergency victims.
Solutions to increase' the accuracy of mobile networks already exist in which mobile clients are located with the help of supplementary information (e.g., postal-code information, streets, town names, etc.). Accuracy is further improved by using the time taken by the signal to reach the mobile device. But due to lack of directional information, users can be located anywhere in a circular band (or a section of a circular band) around a base station, so uncertainty remains.
A Wireless World
It's important to solve indoor positioning problems, because by 2005 there will be 184 million U.S. wireless subscribers (Jupiter Research, 2001). Moreover, according to the National Emergency Number Association, more than 30 percent of 911 calls in the United States originate from mobile phones--a number expected to soon outpace 911 wire-line calls.
A multitude of applications and services would benefit from indoor positioning and navigation. Location-positioning technologies such as the Global Positioning System (GPS) and initiatives such as the U.S. Federal Communications Commission's E-911 mandate generated a lot of interest in location-based services (LBSs). However, despite GPS technology and the positioning capabilities of cellular networks, millions of square meters of indoor space (i.e., office buildings, shopping malls, airports, convention centers, etc.) are out of reach.
During the last decade, however, advances in location positioning technology made it possible to locate objects and people indoors at an accuracy of up to +/- three feet. Table 1 indicates companies actively doing location research, some of which are already deploying indoor LBS applications.
Promising Indoor LBS Applications
Indoor positioning technologies relate people, objects and events in space. Alert-based LBSs, also called…