A novel yet practical method of using lighting circuits as wireless networking points has been developed by the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute HHI in Berlin, Germany. Given the modern tendency to replace incandescent bulbs with massed-LED equivalents, it only makes sense for a method to transmit data using a handful of the LEDs to be considered.

The prototype nets a whopping 800mb/sec from an average-sized bulb, in which the ~LEDs are able to pulse in all of the four colours of red, green, blue, or white, independently of one another. Fitted in the light socket above laptop users, this means the individual elements can pulse quicker than the human eye can catch, whilst still keeping the same light level emitted on average so no flickering is detected by human eyesight.

This optical wireless LAN is of course dependent on data cables sent to the light socket, and the ability to receive optical signals by the laptop or tablet PC below them. But, ironing out these little problems, results in a HD film sent to a laptop in ten seconds, or enough bandwidth upload to commence a sensory simulation interface with a third party.

The first proof of concept attempts, presented at the end of May 2011, on site at the project in Rennes, France was capable of a sustained transfer rate of just 100 megabits per second, using LEDs in the ceiling that light up more than ten square meters (90 square feet). The receiver could be placed anywhere within this radius, so long as it was pointing at the light, but only one connection at a time was possible.

That has now altered in the prototype, and any number of computers under the LEDs can share the bandwidth as with any other wireless system. Of course, the more computers present, the lower the bandwidth available to each. The test was with four laptops and four different films. As Dr. Anagnostis Paraskevopoulos from the HHI put it: “This means that we transferred four videos in HD quality to four different laptops at the same time.“

Regular LEDs can be turned into optical WLAN with only a few additional components thanks to visible light communication (in short, VLC). The lights are then not just lighting up, they also transfer data. They send films in HD quality to your iPhone or laptop, with no loss in quality, quickly and safely.

“The fundamentals of visible light communication (VLC) were developed together with the industry partners Siemens and France Telecom Orange Labs,“ said the expert. At HHI, the team of project manager Klaus-Dieter Langer is now further developing the new technology. “For VLC the sources of light – in this case, white-light LEDs – provide lighting for the room at the same time they transfer information. With the aid of a special component, the modulator, we turn the LEDs off and on in very rapid succession and transfer the information as ones and zeros. The modulation of the light is imperceptible to the human eye. A simple photo diode on the laptop acts as a receiver. As Klaus-Dieter Langer explains, “The diode catches the light, electronics decode the information and translate it into electrical impulses.”

One advantage is that it takes only a few components to prepare the LEDs so that they function as transfer media. One disadvantage is that as soon as something gets between the light and the photo diode (for example, when someone holds their hand over the diode) the transfer is halted.

The scientists emphasize that VLC is not intended to replace regular WLAN, PowerLAN or UMTS. It is best suited as an additional option for data transfer where radio transmission networks are not desired, not possible, or as a backup network for seamless transference.

The new transmission technology is suitable for hospitals, for example, because radio transmissions are not allowed there, since they interfere with the operation of many sensitive diagnostic devices. As a plus in the same environment, because optical signals don't have the same interference problems, the lighting in the OR or in wards, can itself be used to remotely monitor or control the diagnostic equipment hooked up to the patient. Someone's not likely to wave their hand over the top of a mobile X-ray machine during operation, but an optic wireless network means that X-ray can be connected to a telehealth network seamlessly, the moment it is put in a LED-lit room.

The HHI scientists will showcase how videos are transmitted by light in Hall 11.1, Booth 8 at the International Telecommunications Fair IFA (Internationale Funkausstellung IFA) in Berlin from September 2-7, 2011.

References

Data are traveling by light

IFA 2011 - International Telecommunications Fair