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WTF is... Li-Fi?

Optical data transfer's new leading light?

Feature Forget about Wi-Fi - the future of home wireless networking is, according to boffins, the light bulb.

So say a number of researchers and technologists who are looking to light to provide the next step in high-speed data networking in the home.

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The principle is simple: turn a light on and off so rapidly that the human eye can't see the flicker, but a photodetector can nonetheless pick up the stream of 1s and 0s the blinking bulb is transmitting. Compress the data, and you up the throughput even more. Old-style filament bulbs and fluorescent tubes aren't up to the task, but new, LED-based lighting is.

It's not hard to envisage home lighting with an integrated photodetector - to pick up signals sent back from networked devices - and perhaps a powerline adaptor on board to maintain a connection over electrical wiring back to the router.

The technique is called Visible Light Communications - or VLC, not to be confused with the open source media player of the same name - but the companies springing up to deliver the technology are already branding it "Li-Fi". The similarity to the name "Wi-Fi" is deliberate: they hope VLC will become as ubiquitous a networking technology as 802.11 has become.

Lightbulbs, lightbulbs everywhere

One of VLC's key proponents, Harald Haas of the University of Edinburgh, reckons that isn't hyperbole. With tens of billions of regular lightbulbs installed in homes and offices across the globe, as they're replaced with LED light sources, Li-Fi can be a communications technology that can be found almost everywhere.

Li-Fi bulbs will inevitably be more costly than regular LED bulbs, but then the potential volumes will, Haas reckons, push prices right down.

How Li-Fi works

More to the point, Li-Fi could be used in almost every location where regulations forbid the use of Wi-Fi: aircraft cabins and hospitals, to name but two. And light isn't affected by the spectrum regulations that govern how radio frequencies can be used.

Of course, getting it out of the lab and into the living room - and every other space illuminated by a lightbulb - is another matter.

From Palm Pilots to high-speed data

Germany's Fraunhofer Institute, best known for developing the MP3 audio codec, runs a photonics lab in Dresden. Earlier this year, it said it had created a wireless optical link capable of delivering data at the rate of 3Gbps.

Fraunhofer's technology isn't true VLC - it uses infrared light. So it has the backing of the IrDA, the Infrared Data Association, the organisation founded in 1993 to oversee device-to-device infrared communications standards. You know, beaming business card details from one Palm Pilot to another, or early wireless printing kit, or even linking a computer to an old Nokia phone as a modem.

Fraunhofer boffin works on IR board

A Fraunhofer boffin tweaks the Institute's IR tech

Hardly anyone builds IrDA ports into devices these days - USB, Bluetooth and Wi-Fi are faster and don't require line of sight. But the IrDA is looking to VLC to give it a new lease of life.

At the end of 2011, it pledged to work to define a new standard for 5Gbps and 10Gbps infrared communications, an effort building on the 1Gbps the existing Giga-IR standard supports. The Fraunhofer kit supports Giga-IR.

At these higher speeds, IrDA believes its updated standard could replace the likes of HDMI and USB 3.0.

D-Light delight

Meanwhile, Haas, together with Ediburgh University colleague Gordon Povey, continues to work with visible light. They and their team at the college's D-Light - "Data Light" - project have created kit capable of 130Mbps data transfer rights. A lot slower than Fraunhofer's rig, to be sure, but one delivered by off-the-shelf parts rather than custom lab components. Povey and Haas believe they can push that speed to at least 1Gbps. Other Li-Fi proponents claim 10Gbps will be possible with specially designed LED lightsources.

Both boffins also run PureVLC, a company founded to commercialise Li-Fi technology on behalf of the University, and this month PureVLC claimed to have sent the first text message send by LED to an unmodified Android handset.

PureVLC's 'Smart Lighting Development Kit' board

Coming soon: PureVLC's 'Smart Lighting Development Kit' board

To be fair, the data rate was a low 2.5Kbps and it requires a special app to control the handset's cameras and detect the message. But PureVLC's demo showed that messages can be sent with low-cost kit and that doing so doesn't register with the human eye.

PureVLC is also promising to release a "Smart Lighting Development Kit", a full duplex VLC system that connects to standard LED light fixtures, in Q2 2012.

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