Data Are Travelling by Light

Foto: Two people use the VLC-technology

Just imagine the following scenario: four people are comfortably ensconced in a room. Each one of them can watch a film from the Internet on his or her laptop, in HD quality. This is made possible thanks to optical WLAN. Light from the LEDs in the overhead lights serves as the transfer medium. For a long time, this was just a vision for the future. However, since scientists from the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute HHI in Berlin, Germany, have developed a new transfer technology for video data within the scope of the OMEGA project of the EU, its implementation in real life is getting markedly closer.

“The fundamentals of visible light communication (VLC) were developed together with industry partners,“ said Doctor Anagnostis Paraskevopoulos from the HHI. At HHI 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 the project manager Klaus-Dieter Langer explains, “The diode catches the light, electronics decode the information and translate it into electrical impulses, meaning the language of the computer.“

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 his hand over the diode) the transfer is impaired. Laptops, Palm devices or mobile telephones are all potential end devices.

The scientists emphasise 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 or not possible – without needing new cables or equipment in the house.

The new transmission technology is suitable for hospitals, for example, because radio transmissions are not allowed there. Despite this fact, high data rates must be transmitted without losses and unzipped, according to the experts. If part of the communication occurs via the light in the surgical room, this would make it possible to control wireless surgical robots or transmit x-ray images.

Currently the scientists are developing their systems toward higher bit rates. “Using red-blue-green-white light LEDs, we were able to transmit 800 Mbit/s in the lab,“ said Langer. “That is a world record for the VLC method.“; Source: Fraunhofer Institute, Heinrich-Hertz-Institut HHI