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Innovation: What's the right path for indoor satnav?

Tue, 09/21/2010 - 11:24am
New Scientist

Tracking down one of the last few parking spots in the cramped confines of a dimly lit multi-storey car park is not among life's pleasures. German car maker BMW thinks it has the answer: an indoor positioning system (IPS) that guides drivers to that precious parking spot and later helps them find their car again – through smart use of the car's anti-roll inertial sensors and a mapping app on a cellphone.

BMW's was one of many ideas unveiled at last week's Indoor Positioning and Indoor Navigation (IPIN) conference in Zurich, Switzerland, a gathering of engineers hoping to mimic the runaway success of satnav technology – but this time indoors.

IPS proponents want to pepper public buildings with wireless transmitters to help people locate their departure gate at an airport, say, or a particular store in a vast mall, or an exhibit in a labyrinthine museum. IPS will also be able to track moving targets, letting us locate friends in a multi-storey building regardless of what floor they are on.

But the technology could be a while coming to a public building near you because there is no broad agreement on which technology is best for pinpointing people and objects deep within buildings. The different radio-reflecting and absorbing materials in the built environment mean that radio waves, commonly used in outdoor positioning systems like GPS and the European Union's upcoming Galileo network, cannot reliably negotiate complex architectural geometries.

Time and strength

Consequently, engineers are trialling a variety of different methods to find the most reliable. Two leading contenders are called received signal strength (RSS) and time of arrival (ToA).

RSS relies on knowing the strength of a radio signal at its source and monitoring the drop-off with distance. Given a number of static transmitters, the receiver can work out where it is by triangulation. RSS techniques can use Wi-Fi, Bluetooth and ZigBee – an ultra-low-power version of Bluetooth – radio networks.

ToA, on the other hand, involves reading time stamps beamed from transmitters in known positions and calculating a position by comparing the times when signals from different transmitters arrive. It is the method at work in GPS.

Rivals play tag

At the Nokia World trade show in London last week, Fabio Belloni of the Nokia Research Lab in Tampere, Finland, and his colleagues wore slim, credit-card-sized radio tags to track their movements to within 30 centimetres using an RSS approach. An upgrade of Nokia's technology, presented by Belloni's colleagues at IPIN, also included an inertial sensor, allowing dead reckoning of the user's motion in between accurate IPS fixes.

A rival system is being offered by Omnisense, a geolocation firm based near Cambridge, UK, which presented the technology to investors at the Meerkats and Avatars invention show in Cambridge this month. Omnisense uses ZigBee radio, inertial sensors and a GPS receiver in its RSS tags – allowing them to switch seamlessly between indoors and outdoor locations, says the firm's Andy Thurman.

The technology could help track miners both above ground and underground, people suffering from dementia – and cattle. Working out when a cow is ovulating is important to farmers – and they "present" in a different direction to bulls in the herd when this happens. "The inertial sensors will tell us this," Thurman says.

GPS emulator

One of the most interesting ideas at IPIN was a ToA approach that mimics the format of the GPS signal – and which is locked to the GPS atomic clock to boot – allowing the satnav receiver technology to be used indoors as well as out. Developed by Locata Corporation of Canberra, Australia, the system places radio nodes that beam out GPS timing data around an area or building of interest. It's designed to aid the military if GPS is being jammed – indeed, the US air force bought one of the systems this week. Chief executive Nunzio Gambale is investigating a range of consumer applications as well.

But these varied systems leave the standardisation problem unsolved. The Open Mobile Alliance, a global cellphone industry body, is looking into how the next generation of 3G technology – currently called LTE, for Long Term Evolution – might be harnessed to provide a standard positioning protocol. But Kanwar Chopra, an engineer with CSR in Cambridge, UK, is sceptical.

"I don't think there is ever going to be one particular technology for indoor location sensing," he told the UK National Microelectronics Institute's Future World Symposium in London last week. "As we go deeper and deeper indoors, accelerometers and gyros have to do the work. Radio signals are just not designed for location sensing in all environments. It's always going to be a fusion of multiple signal types."

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