Regular light-emitting diodes (LEDs) can be turned into an optical wireless local area network (WLAN) with only a few additional components, thanks to visible light communication (VLC).
Researchers from the Fraunhofer Institute for Telecommunications' Heinrich Hertz Institute (HHI) have transferred data at a rate of 100 Mbit/s without any losses, using LEDs in the ceiling that illuminate over 90 square feet. A receiver can be placed anywhere within this radius, which is currently the maximum range. The scientists successfully transferred four videos in high-definition quality to four laptops at the same time.
“The fundamentals of visible light communication were developed together with industry partners Siemens and France Telecom Orange Labs,” said Dr. Anagnostis Paraskevopoulos from the HHI. At the institute, the team of project manager Klaus-Dieter Langer is further developing the 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,” explains Klaus- Dieter Langer. “The diode catches the light, electronics decode the information and translate it into electrical impulses, meaning the language of the computer.”
It takes only a few components to prepare the LEDs so that they function as transfer media. However, as soon as something gets between the light and the photo diode, the transfer is impaired. VLC is not intended to replace WLAN. 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.
The new technology is ideal for hospitals, for example, since radio transmissions are not permitted. Despite this fact, high data rates must be transmitted without losses and unzipped. 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.
The scientists are currently developing their systems toward higher bit rates. “Using red-bluegreen-white light LEDs, we were able to transmit 800 Mbit/s in the lab,” said Klaus-Dieter Langer.