Flickering lights are annoying but they may have an upside. Visible light communication (VLC) uses rapid pulses of light to transmit information wirelessly. Now it may be ready to compete with conventional Wi-Fi.
“At the heart of this technology is a new generation of high-brightness light-emitting diodes,” says Harald Haas from the University of Edinburgh, UK. “Very simply, if the LED is on, you transmit a digital 1, if it’s off you transmit a 0,” Haas says. “They can be switched on and off very quickly, which gives nice opportunities for transmitting data.”
It is possible to encode data in the light by varying the rate at which the LEDs flicker on and off to give different strings of 1s and 0s. The LED intensity is modulated so rapidly that human eyes cannot notice, so the output appears constant.
More sophisticated techniques could dramatically increase VLC data rates. Teams at the University of Oxford, England and the University of Edinburgh, Scotland are focusing on parallel data transmission using arrays of LEDs, where each LED transmits a different data stream. Other groups are using mixtures of red, green and blue LEDs to alter the light’s frequency, with each frequency encoding a different data channel.
Li-Fi, as it has been dubbed, has already achieved blisteringly high speeds in the lab. Researchers at the Heinrich Hertz Institute in Berlin, Germany, have reached data rates of over 500 megabytes per second using a standard white-light LED.
The idea of using light to send information has been around for well over a century. Alexander Graham Bell sent a wireless phone message in 1880 using his invention known as the Photophone. The reason that invention never got the traction that Bell’s later invention did – the telephone – is that the light bulbs of the time were pretty primitive.
Dr. Harald Haas demonstrated his Li-Fi prototype at the TEDGlobal conference in July.
Today, we have LED lights that are both energy-efficient and more technologically advanced because they can be more finely controlled.
Academic and commercial interest in VLC has accelerated in recent years. The increasing popularity of LED lights makes light-based technology more practical and economical. Also, the exponentially growing demand of wireless communication devices has taxed radio spectrum, resulting in a need to find alternatives.
Dr. Haas gave a debut demonstration of what he called a Li-Fi prototype at the TEDGlobal conference in Edinburgh, Scotland in July 2011. He used a table lamp with an LED bulb to transmit a video of blooming flowers that was then projected onto a screen behind him. The prototype can be built economically in part because it uses cheap off-the-shelf parts that cost just a few dollars, he said. “There is no antenna,” he said.
Dr. Haas then stuck his hand under the light to block it from the receiver, and the video immediately paused. After resuming the video, he also turned the lamp away from the receiver, which also paused the video.
The speed of data transmission was about 10 megabits per second, though Dr. Haas is aiming to have it reach 100 megabits per second by the end of the year. Siemens, which is also working on VLC, last year announced that it was able to transmit at speeds of 500 megabits per second within a five-meter distance.
Light-based data transmission technology is attractive because it allows wireless communication without the use of radio gear, which can be dangerous in places like oil platforms (where it can cause sparks) and underwater (where the salt conducts electricity), or on planes (where it can interfere with other radio equipment). VLC could be also integrated into medical devices and hospitals where Wi-Fi is banned.
In addition, transmissions can be stopped simply by blocking the light, and thus can be stopped by walls, so there is less risk of data leaking out of a house or office. And researchers say they believe that signals can piggyback on lights that are already in use – street lamps, car headlights or room lighting.
Li-Fi could free up bandwidth, especially since much of the infrastructure is already in place.
“There are around 14 billion light bulbs worldwide, they just need to be replaced with LED types that transmit data,” says Haas. ”We reckon VLC is a factor of ten cheaper than Wi-Fi.”
Source: New Scientist Magazine