Original URL: http://www.theregister.co.uk/2011/08/02/vlc_breakthrough/

Boffins shine 800Mbps wireless network from flashlight

LEDs torch LAN record

By Rik Myslewski

Posted in Broadband, 2nd August 2011 20:14 GMT

German researchers have discovered how to fill a room with 800 megabits per second of wireless data using an inexpensive LED setup.

"Using red-blue-green-white light LEDs, we were able to transmit 800Mbit/s in the lab," said researcher Klaus-Dieter Langer. "That is a world record for the [visible light communication] method."

Langer, working at Berlin's Heinrich Hertz Institute, an arm of Fraunhofer Institute for Telecommunications, also described an earlier experiment that reached 100Mbit/s using only white-light LEDs.

"We turn the LEDs off and on in very rapid succession and transfer the information as ones and zeros," he explained. "The modulation of the light is imperceptible to the human eye.

On the receiving end is a simple photo diode, and circuitry that converts the diode's signals into a digital data stream. According to Langer, advantages of this method include the simplicity of converting the LEDs into signal-sending devices, and the elimination of cabling as a signal-transferring medium.

In the 100 Mbit/s experiment, the signalling LEDs were placed on the ceiling, and the transmission was error-free in an area of 10 square meters, received by a group of four photo diode–equipped laptops.

"We transferred four videos in HD quality to four different laptops at the same time," said another HHI researcher, Anagnostis Paraskevopoulos.

Using visible light as a signaling medium rather than radio waves has clear advantages in areas such as hospitals and aircraft where radio transmission is not possible and where cabling would be prohibitively expensive.

The most obvious disadvantage of visible light communication (VLC) is that the signal can be easily blocked by any solid object – a hand moving between the LEDs and the photo diode, for example. The inability for light to penetrate walls also limits VLC to special-case scenarios.

As limited as VLC may seem, when The Reg spoke in June with Aicha Evans, wireless engineering manager at Intel, she told us that "a lot of people are talking about visible light."

Although Evans admitted that "it's still science fiction," VLC may very well show its value in the last few meters of a data stream. If at this early stage of its evolution it's already being demonstrated at 800Mbit/s speeds, VLC may very well prove to be a serviceable high-speed, within-four-walls broacast WLAN in future implementations. ®