AN UNLIKELY backup for Global Positioning System (GPS) is emerging: Wi-Fi. In the concrete canyons of city centres, GPS satellite positioning systems often fail because high buildings block the signals. In cities and inside cavernous complexes like shopping malls a Wi-Fi based positioning system developed in the U.S. and the U.K. works best where GPS fails.
The developers predict that Wi-Fi could become central to new location-based applications because cheap Wi-Fi technology is already appearing on a raft of gadgets like PDAs, cellphones and laptops faster than more expensive GPS receivers are.
Connecting wirelessly
Emergency services in particular could find the system an essential backup, they say.
Wi-Fi allows people to connect devices wirelessly to the Internet. In coffee bars, libraries, universities, airports, phone booths and other public places base stations are springing up.
To announce its presence to devices within a range of around 100 metres, each base station broadcasts a radio signal. A unique network address code that identifies the base station is incorporated by this signal.
Software that constantly records the radio signal strengths from nearby base stations has been developed by Anthony LaMarca of the University of Washington in Seattle, and colleagues at Intel's research labs in both the U.S. and the U.K. It can identify the origin of the signal from a database giving the location of 26,000 Wi-Fi base stations in the U.S. and the U.K.
According to the report published in New Scientist, using the signal strength from at least three base stations, it can then triangulate the user's location.
``This is a poor man's GPS,'' says team member Bill Schilit of Intel Research in Santa Clara, California. The new system, called Place Lab, is not as precise as GPS, at the moment. Whereas the GPS average is 8 to 10 metres it can provide accuracy to within 20 to 30 metres.
Improved algorithms
But with improved algorithms that take into account, say, the height of the base station above the ground, or the building materials in the vicinity, LaMarca says ``we could get on a par with GPS'' in an area as densely served with Wi-Fi as downtown Seattle.
The growth of Wi-Fi means all urban areas should one day have similar blanket coverage. Once a user has Wi-Fi they won't have to buy extra hardware to use Place Lab, and the software can be downloaded for free from www.placelab.org. — Our Bureau
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