Li-Fi

What is Li-Fi?

Li-Fi is a term often used to describe Visible Light Communications technology applied to high speed wireless communications.

It acquired this name due to the similarity to Wi-Fi, only using light instead of radio.
Wi-Fi is great for general wireless coverage within buildings, and Li-Fi is ideal for high density wireless data coverage in confined areas and for relieving radio interference issues, so the two technologies can be considered complimentary.

Image from Wired UK Feb 2012
Li-Fi is typically implemented using white LED light bulbs at the downlink transmitter.  These devices are normally used for illumination only by applying a constant current.  However, by fast and subtle variations of the current, the optical output can be made to vary at extremely high speeds. Unseen by the human eye, this variation is used to carry high speed data.

Why you need to get a Li-Fi!

Radio spectrum is congested but the demand for wireless data doubles each year.  Everything, it seems, wants to use wireless data but the capacity is drying up.  Wireless radio frequencies are getting higher, complexities are growing and RF interference continues to grow. So what can carry this excess demand in the future?
The solution is Li-Fi. Direct modulation of LED devices is a low cost, secure, and safe way to transmit data, and there is an abundance of free visible light spectrum.  High intensity LEDs used in light bulbs, flash lights and cameras can transmit very high data rates, faster than Wi-Fi!

Will Li-Fi be the new Wi-Fi?

• 28 July 2011 by Jamie Condliffe
• Magazine issue 2822. Subscribe and save

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 and the University of Edinburgh 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. Haas has set up a spin-off firm to sell a consumer VLC transmitter that is due for launch next year. It is capable of transmitting data at 100 MB/s - faster than most UK broadband connections.

Once established, VLC could solve some major communication problems. In 2009, the US Federal Communications Commission warned of a looming spectrum crisis: because our mobile devices are so data-hungry we will soon run out of radio-frequency bandwidth. Li-Fi could free up bandwidth, especially as much of the infrastructure is already in place.

"There are around 14 billion light bulbs worldwide, they just need to be replaced with LED ones that transmit data," says Haas. "We reckon VLC is a factor of ten cheaper than Wi-Fi." Because it uses light rather than radio-frequency signals, VLC could be used safely in aircraft, integrated into medical devices and hospitals where Wi-Fi is banned, or even underwater, where Wi-Fi doesn't work at all.

"The time is right for VLC, I strongly believe that," says Haas, who presented his work at TED Global in Edinburgh last week.

But some sound a cautious note about VLC's prospects. It only works in direct line of sight, for example, although this also makes it harder to intercept than Wi-Fi. "There has been a lot of early hype, and there are some very good applications," says Mark Leeson from the University of Warwick, UK. But I'm doubtful it's a panacea. This isn't technology without a point, but I don't think it sweeps all before it, either.