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Cellphones could guide high-rise rescuers
05 September 2007
NewScientist.com news service
Paul Marks

A man working in a skyscraper has a heart attack and phones for help, but he fails to tell the emergency operator which floor he's on. Paramedics then have to waste precious minutes searching the 40-storey building, and the man dies.

Researchers at the University of Toronto in Canada and chipmaker Intel have developed a system that they say could help prevent such deaths. Called Skyloc, it can estimate the location of callers inside high-rise buildings to within two floors. If used in New York's 102-storey Empire State Building, it could cut the floor space that would have to be searched from 204,000 to 2000 square metres.

In a city, cellphones pick up signals from many tens of masts but to make a call they only use the masts sending the strongest signals. Signals can be used to triangulate a phone's position using the three nearest masts, but it is only accurate to 50 metres and can't distinguish between floors.

Skyloc exploits the fact that every point in a city is bathed in a unique combination of radio signals from hundreds of masts, each at different strengths and frequencies. Skyloc uses this miasma to generate a "position fingerprint" that is unique both to the phone's horizontal coordinates and vertical position.

On each floor of three high-rise buildings, a team led by Alex Vershavsky of the University of Toronto recorded the signals received from 29 masts. Specially developed software successfully allowed a phone to transmit these position fingerprints during calls. These were then matched against a database of all fingerprints from the building to pinpoint the caller's floor. Vershavsky says lives could be saved if all tall buildings were "radio-mapped" and phones were programmed to transmit their position fingerprints.

Amanda Goode, a UK-based expert in cellphone forensics, sees other uses for the technology. "The ideas behind this could be useful in kidnap or serious crime investigations," she says.

From issue 2620 of New Scientist magazine, 05 September 2007, page 32

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