This article is reproduced with the permission of New Scientist for exclusive use by Nova users.

Indoor 'sat-nav' could save firefighters
13 December 2007
From New Scientist Print Edition.
Duncan Graham-Rowe

The recent tragic deaths of nine American and four British firefighters in warehouse fires throws the perilous nature of the job into all-too-sharp relief. But while finding a way through a blazing, smoke-filled building is never going to be easy, experts are agreed that the risks firefighters face could be significantly reduced if they, and their commanders, knew exactly where they were in a smoke-filled building at all times. That way, help could be quickly summoned - or sent - to the right place when it's needed.

Now a tracking system that does just that has been developed by Thales, a French aerospace company. The firm likens its technology to an indoor version of the Global Positioning System: a display worn by the firefighter shows their position in a building, and a screen on the commander's computer console does likewise.

Why not use regular GPS? It cannot be reliably used indoors because the signals from its satellite network are too weak to reliably penetrate roofs, walls and ceilings. Even if the signals do get through, they reflect off surfaces and confuse receivers - inducing errors that ruin attempts to get an accurate position fix, says Michael Quinlan, technical director of Thales's lab in Reading, UK.

To overcome this, the Thales Indoor Positioning System (IPS) ingeniously splits the process in two: first, a ground radio network establishes the position of firefighters inside a building with respect to each other and to stationary firetrucks outside. The GPS positions of those firetrucks are then used to establish the positions of the firefighters in the building. The result is that the GPS signals aid position fixing, but do not need to penetrate the burning building.

At the heart of the IPS are radio transmitter/receivers the size of a pack of cards, which are worn by the firefighters and installed in the firetrucks and the command console. Once firefighters enter a building, the IPS transceivers establish an ad-hoc radio network between themselves. The time it takes their signals to reach each transceiver and bounce back lets each node work out how far away the others are, says Quinlan.

But merely knowing their relative distances is little use. What's needed is the nodes' positions in the real world. So the system correlates the GPS fixes of at least two firetrucks outside with their positions in the ad-hoc network, and then uses this information to calculate the global position of everyone in the network - and therefore the location of the firefighters.

However, calculating distances using radio pulses is not easy, because like GPS, the signal can reflect off building surfaces. To avoid this destructive effect, IPS uses ultrawideband signals.

In UWB, the radio pulses are sent out across a wide swathe of frequencies instead of just one, in this case in the band between 3.1 and 4.8 gigahertz. This extra bandwidth means that even if some parts of the signal are fouled by interference, others will not be. The upshot, says Quinlan, is that reflection is no longer a problem.

Indoor tracking systems have been proposed before - using signals from Wi-Fi and cellphone networks. But in a fire, the reliability of such systems cannot be guaranteed, since antennas may have been destroyed.

Hampshire Fire and Rescue Service demonstrated IPS at Thales's lab this week, showing how it can guide disoriented firefighters in a building - or have them rescued quickly. And when searching for survivors in a large hotel, IPS lets firefighters know which rooms have already been searched, says Hampshire's fire strategist Mick Johns. "Knowing where firefighters have been is important for ensuring rooms aren't searched twice or, crucially, that some have been missed."

While firefighters and earthquake rescue teams are Thales's main focus, the firm has one eye on the consumer market. It is working on an IPS for GPS-enabled cellphones that will let users extend their navigation indoors, to places like shopping malls and airports. But since that would mean persuading mall and airport operators to fix IPS transceivers in their buildings, too, it's some way off, says Quinlan.

From issue 2634 of New Scientist magazine, 13 December 2007, page 24

For the latest from New Scientiist visit www.newscientist.com