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White LEDs offer radio-free wireless option

A photonic alternative to WLAN has been shown to exceed 100 Mbit/s and could provide bandwidth in a currently unlicensed area of the spectrum, if it can conform to general illumination standards.

Thanks to white LEDs, overhead lighting could soon be used to transmit data over a RF-free wireless connection.

That s according to Joachim Walewski from Siemens Corporate Technology, who has modulated the light emission from white LEDs in order to make a 101 Mbit/s wireless link with a PiN diode photodetector.

“With this, you can have interference-free communication,” Walewski pointed out, adding that the visible spectrum is currently free of any requirements for communication licenses.

Siemens is currently exploring the technology in order to keep pace with a competing Japanese collaboration that expects to bring similar technology to market by 2011, Walewski says.

His Munich-based team claims to be the first to have boosted data transmission rates by focusing on specifically detecting blue light. Removing noise arising in the yellow part of the spectrum, from light emitted by the LED s phosphor, provides an order-of-magnitude increase in data transmission rates.

The results were presented by Walewski s collaborators at the Technical University of Eindhoven s COBRA Institute when the European Conference and Exhibition on Optical Communication hit the German capital in September.

The team, which also included a contingent from the Berlin-based Heinrich-Hertz Institute, presented the work as an intermediary early stage between exploratory and full development research. So early stage, in fact, that it uses LEDs bought from the local electronics shop, instead of from Siemens subsidiary Osram.

“The next step is of course using large area assembled chip arrays like the Ostar,” Walewski confirmed.

In the change from radio to visible frequencies many protocols that allow multiple messages to be sent remain unaltered, like time-division multiplexing. However, some of the familiar properties of light provide an important differentiator, such as signals being blocked by physical barriers like walls.

“You can have spatial multiplexing because, if you look at the ceiling in your office, the lamp in the right corner doesn t really interfere with the lamp in the left corner,” Walewski explained.

Overhead light-based data transmission technology already exists, for example as provided by a firm called Talking Lights, who make systems that transmit GPS-like data indoors, where it s otherwise not provided.

However, Walewski points out that for the technology to really become widely adopted, it s important to keep lighting standards as a primary consideration, alongside data transmission capability.

“I haven t really seen anything out there that really is totally compliant with an existing lighting system,” he said. “Everything I've seen so far is home built demonstrators that were specially designed to fulfill the task of communications.”

“We can t just tell lighting manufacturers what to do with their lighting. We have to adapt to them.”

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