Tracking users becomes much more challenging indoors, however. Assisted GPS can lose much of its accuracy due to ceilings, walls, and other obstructions, while cellular techniques don’t even come close to making the grade: a 120-meter error range may let you spot a flashing restaurant sign down a city block, but even a five-meter miss in a skyscraper could put a user on a completely different floor. Although this isn’t an issue in many applications, it could mean the difference between life and death to soldiers trying to identify friends and foes in an urban warfare setting or firefighters searching for victims in a blaze.So what kind of technology could be used once a person steps inside and takes the elevator up, up, and away? One possibility is the popular wireless networking technology known as 802.11, or Wi-Fi. Numerous wireless carriers have begun installing Wi-Fi transceivers in hotels, cafs, and other commercial buildings to deliver high-speed Internet access to mobile users. This expanding infrastructure can also be used to locate people indoors, says Antti Korhonen, CEO of Helsinki, Finland-based Ekahau, which builds software that enables Wi-Fi location finding. This past spring, consulting firm Accenture used Ekahau’s software in a pilot project for New York’s Metropolitan Museum of Art: patrons wandering the Met’s cavernous halls and stopping at a few of its two million works of art received information about the pieces in front of them with the click of a PDA button.
To achieve this virtual docent delivery, Accenture employees drew a detailed map of the exhibit area-a process that can take an hour for every 1,000 square meters covered, says Korhonen. Once the map was uploaded into a computer, employees walked around the museum, clicking on the map every three meters and recording the network’s signal strength. Each location was matched to a specific signal strength, so that when museumgoers accessed the network, it knew where they were. With accuracy ranging from one meter to 20 meters, says Korhonen, Wi-Fi mapping is generally more precise than cellular triangulation. Big commercial applications will begin to emerge this year, he says; for instance, a German retail chain is using Wi-Fi in a pilot project to push information to shoppers depending on their location in a store. Since devices on the first floor of a building will measure significantly different signal strengths than those on other floors, Ekahau’s technology can also solve the up-down problem, says Korhonen. “There is no way we could miss the floor,” he says.
If location is calculated based solely on which Wi-Fi access point is closest, though, and not on painstakingly assembled signal-strength maps, the technology often places people on the wrong floors. And whether used indoors or out, a Wi-Fi transceiver covers a limited geographical area, with a radius of only about 90 meters. It’s also susceptible to signal interference that can affect accuracy and is not particularly secure: nefarious characters might be able to determine your location based on your signal. According to Bill Yeager, a Sun Microsystems engineer working on location-aware computing, someone who knows that you are in a pizza place rather than at home could say, “Let’s go over there and steal his home theater, or whatever they want to take.”
It’s not hard to imagine applications that will require greater accuracy, not to mention reliability and security. Luckily, another wireless technology could fill the gap: ultrawideband. Ultrawideband uses on/off energy bursts only billionths of a second long at extremely low power (one-thousandth the power of a traditional cell phone) over a large frequency spectrum. These tiny bursts enable the technology to deliver data at speeds of hundreds of megabits a second, as well as provide ultraprecise positioning. And as with GPS or Wi-Fi, ultrawideband could be incorporated into a cell phone or PDA.
Distance can be determined by measuring how long it takes a pulse to travel between an ultrawideband transmitter and receiver, and position can be determined via triangulation if at least three signals are received. “If you have four locations, you can do vertical mapping,” says Bruce Watkins, president and chief operating officer of Pulse-Link, a San Diego-based ultrawideband company. That enables the system to figure out how high an object is off the ground-or which floor of an office building or hotel a person is on. Because the technology-unlike Wi-Fi-relies on ultrashort pulses, the receiver can determine time of arrival in picoseconds, allowing it to establish location to within centimeters, according to Watkins. Yet because ultrawideband is not as far along in its development and deployment as Wi-Fi, ESRI’s Spinney, for one, sees it losing out on many applications, such as tracking consumers through malls or airports-where Wi-Fi systems are already being installed-and sending them promotional offers.