Meet Li-Fi, the LED-based alternative to household Wi-Fi
This article was taken from the February 2012 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
Using off-the-shelf electronics, he can stream videos using an ordinary light bulb fitted with signal-processing technology of his own design. The lamp shines directly on to a hole cut into the oblong box on which it sits. Inside this box is a receiver that converts the light signal into a high-speed data stream, and a transmitter that projects the data on to a screen as a short video. If Haas puts his hand in front of the lamp, excluding the light, the video stops.
Haas, 43, holds the chair of mobile communications at Edinburgh University's Institute for Digital Communications. His demo is scientifically groundbreaking: it proves that large amounts of data, in multiple parallel streams, can be transferred using various forms of light (infrared, ultraviolet and visible). The technology, he says, has huge commercial potential. His device can be used with regular lighting and electronics -- albeit reconfigured -- and could transform the way we access everything from video to games, accelerating the speed of internet access by many hundreds of megabits. It could let us download movies from the lamps in our homes, read maps from streetlights and listen to music from illuminated billboards in the street.
Haas's discovery is based on a subset of optical technology called visible light communication (VLC), or Li-Fi, as it has been dubbed. VLC exploits a hack of human perception: light-emitting diodes can be switched on and off faster than the naked eye can detect, causing the light source to appear to be on continuously. Rapid on-off keying enables data transmission using binary code: switching on an LED is a logical "1", switching it off is a logical "0". Thereby flows the data.
The potential applications are enormous: divers working at depths could use light to communicate; air passengers could connect to the internet through the LEDs inside the aircraft. Haas sees the technology potentially disrupting industries from telecoms to advertising.
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Research into VLC has been conducted in earnest since 2003, mainly in the UK, US, Germany, Korea and Japan. Experiments have shown that LEDs can be electronically adapted to transmit data wirelessly as well as to provide light. VLC is faster, safer and cheaper than other forms of wireless internet, advocates say -- and so could eliminate the need for costly mobile-phone radio masts.
German-born Haas sits in his office in Edinburgh University. Several of the university's faculties, led by the informatics department, are involved in his project, called D-LIGHT; the university, a sponsor, owns the intellectual property. A month before wired's visit, Haas prompted stunned applause when he demonstrated his technology live to the audience at TEDGlobal in his adopted city. "To my disgrace," he confesses, "I didn't know anything about TED before [my talk]. Now it's like winning the lottery -- every day, I get five to ten emails, all very positive and excited. They are excited because it's easy to comprehend the unique opportunity in this technology."
In person, Haas is calm, humorous and cerebral, unfussed by his academic celebrity and unmotivated, he says, by the prospect of wealth. Married to a fellow German and graduate of the University of St Andrews, he jokes about their young children picking up an Edinburgh burr. He does not seek fame, he says, only for his work to fulfil its potential. "I'm less interested in what may change the world in 20 years' time," he says. "I'm looking into fundamentals of science that could do so within the next few years."
Haas grew up in Nuremberg. His thinking was greatly influenced by his father, an engineer at Siemens. He recalls a teenage fascination with LEDs -- a new technology at the time -- and inventing, at around 13, a rev counter that neighbours wanted to install in their cars. "I played a lot with electronics when I was a kid," he says. "I wanted to understand the transistor, and I wrote an essay [about them] at school. Everyone thought, 'What is this strange guy doing here?'"
He followed his father into Siemens, developing mobile-phone chips in Munich, but grew bored and escaped to academia. In 1995 he went on a scholarship to Mumbai, where he helped Siemens to develop a mobile-phone network. By 1999, he was at Edinburgh University, where he and his tutor, Gordon Povey, now his business partner, developed a patent for the 3G Universal Mobile Telecommunications System, which they sold to Siemens.
His office is now in the university's Alexander Graham Bell building. In 1880, Bell became the first person to send a voice message by modulated light. Using his "Photophone", Bell directed sunlight at a parabolic mirror that captured and projected his vocal vibrations. Sunlight's unpredictability sidelined his idea. Radio transmission seemed more promising.
Now Haas is fulfilling Bell's ambition with LEDs, whose principal technology was discovered more than 100 years ago. LEDs were little used until the late 20th century, when they began appearing in car-instrument panels, infrared handsets and TVs. They are brighter, tougher and more reliable -- if costlier -- than the incandescent bulbs they are gradually replacing.
Haas has a small lab stuffed with equipment, including the now-famoustable lamp and its box of electronics. It was here in 2007 that his research assistant, Mostafa Afgani, first sent data using light signals. Haas's invention centres on how these signals are modulated: the information, embedded within visible light emitted from the LEDs, is transmitted by means of many subtle changes made to the intensity of the light at the ultra-high rate of 100 million cycles per second (100MHz). The photo-detector in Haas's box monitors these tiny variations and converts them back into a digital signal, from which the transmitted information is extracted.
Early in his research, Haas became intrigued by the properties of two wireless-technology systems: multiple-input and multiple-output (Mimo), which employs antennas at both the receiver and transmitter to improve signal; and orthogonal frequency-division multiplexing (OFDM), found in DAB radio and 4G mobile communications.
A weakness of OFDM is its peak-to-average power ratio, which produces wide fluctuations in the signal. But Haas could work this into an advantage for optical communications if he used those variations to crank up intensity. This meant that he could transmit data streams in parallel, and at rates limited only by the number of LEDs. He calls his transmission technique spatial modulation OFDM, or SIM-OFDM. "We exploit three dimensions," he explains. "Time, frequency and space. No one has ever done this before."
Haas, Povey and Afgani founded a company, VLC Ltd, to market their transceiver technology and a seed-funding round was completed last November. A larger "Series A" VC funding round is expected later this year. But the team is in a race to market: rival companies are already selling and trialling VLC products. In Tokyo, Nakagawa Laboratories, where Haas spent a semester in 2003, has developed what it calls underwater visible light communications: a means of picking up a scuba-diver's voice using a microphone in an LED light and sent to another diver. In December 2010, US technology firm LVX started providing light- powered broadband services to six public buildings in the Minnesotan town of St Cloud. LVX says it's demonstrating "fibre optics without the fibre". The company would not comment, but is said to have transmitted data at an unimpressive 3Mbps.
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