Visible Light Communications (VLC), also known as IEEE 802.15.7 “Short-Range Wireless Optical Communication Using Visible Light” is poised to provide a miraculous IP bandwidth breakthrough. IEEE seems excited because it provides a practical wide-band RF alternative.

Professor Harald Haas, Chair of Mobile Communications at the University of Edinburgh and his research team, used the concept of VLC to develop LiFi in labs in the Alexander Graham Bell Building. Bell was born in Edinburgh and attended the University.

Bell demonstrated the first VLC system in 1880, four years after inventing the telephone. He called it a Photophone. It needed strong daylight to work and it flopped. At the 2011 TEDGlobal Conference 131 years later, Prof Haas unveiled his version of VLC, where he coined the term LiFi while demonstrating live streaming video over LiFi on a laptop.

In generic terms, LiFi covers any form of data communications via visible, primarily white light. The visible light spectrum is 380 to 780 nm. It is not the infrared (IR) communication used on most consumer remote controls, although the concept is similar.

In terms of high speed data, LiFi is on the launching pad and 5-4-3, the engines just fired. On 25 November 2015, LiFi shifted from a technical conference curiosity and prototype phenomenon to the real world, with the announcement of a manufacturing partnership forecasting off-the-shelf LiFi product delivery in a year or less.

Where Li-Fi fits into the broadcasting business remains to be seen, but it will assuredly find its place. It could work for video transport. If anyone can find ways to sponsor and sell it, creative broadcast sales people will. GigE networks such as NewTek's NDI support uncompressed HD. GigE video via LED directional light fixtures leads to some interesting "What if?" ideas.

Why LiFi?

One of the goals of LiFi is to augment indoor Wi-Fi where the connection doesn’t need to penetrate walls. The objective is to motivate mobile gear manufacturers to add LiFi as a built-in connection, just as Wi-Fi and Bluetooth were added to cellular. One successful business model that’s been used many times is to flood the market with inexpensive fixed and portable LiFi devices that are instantly useful, such as USB transceivers for laptops.

LiFi takes advantage of the amazing high-speed switching capabilities native to LED lights, which can be switched up to gigabyte bit rates without dimming or other visible artifacts. The lighting infrastructure already exists and is easily expanded and combined with LiFi.

Bits of wireless data are about to become overwhelming. According to Prof Hass, by 2018 an estimated 16 exabytes of data will move across mobile networks. One exabyte = 10¹⁸ bytes = 1 million terabytes = 1 billion Gb.

16 exabytes is equal to streaming 1.8 million years of HD video on the network every month, at 3 Gb/hour. 16 exabytes is equal to the estimated bandwidth for a predicted 1000 Internet devices/person by 2020. Most of the many new devices will belong to the Internet of Things (IOT). The exploding IOT population threatens to saturate wireless RF bands.

In 2020, total IOT and personal traffic on the Internet is predicted to consume as much energy as global air traffic. That’s a lot of traffic to fit in a 30 Ghz band along with everything else RF on the air.

What LiFi is

LiFi is brilliantly simple. Modulate a standard LED bulb with 1s and 0s with the normal state of the LED being 1 (bulb on). The LiFi transmit LED needs to be continuously on to maintain connectivity. Digital zeros cut the light off for micro instants. Otherwise, the transmit LED is always on.

LiFi uses a type of orthogonal frequency-division multiplexing (OFDM) spatial modulation that allows transmission of parallel bit streams modulating the LED. The LED switches off and on so rapidly, data transmission is visually imperceptible to the eye. LEDs aren’t dimmed by data, but the LED’s light output can be dimmed to a point above where the data breaks through the noise (other light).

Prof Haas’ first public simple demonstration at the TEDGlobal Conference showed a $3 LED bulb in a table lamp modulated with his signal processing technology, and a photodiode receiver similarly converting the signal back to a high speed data stream. He demonstrated the technology by streaming HD on a projection screen and waving his hand in front of the photodiode to interrupt the stream. Other Internet videos show reception with solar cells.

What LIFi isn’t

LiFi isn’t a replacement for Wi-Fi. At the moment, LiFi is a method of one-way data transmission with innumerable potential benefits. The rationale is that about 90% of Internet data transmission is one-way.

Two way systems are being developed and tested. They split the spectrum with a visible spectrum downlink and an infrared uplink.

pureLiFi is a light communications Technology Company formed in 2012 as a spin-off from the University of Edinburgh to create OEM components, including LiFi drivers and receivers.

The company recently demonstrated a split-spectrum system at the Barcelona 2015 Mobile World Congress. The system was the Li-Flame CU ceiling unit and the Li-Flame DU desk unit. Together they provided dual 10 Mbps half duplex, using infrared uplink from DU to CU.

Unlike RF, visible light is secure. It doesn’t go through walls. Light is directional and is easily made more directional. Bright light from an LED can be bounced off a wall or ceiling and decoded. Photodiode receivers can be made to be quite directional. Prof Haas envisions photodiodes so small they could be mounted in a clear sphere to mimic an insect’s eye, seeing in all directions simultaneously. Such technology is still under development.

The current laboratory LiFi LAN speed record is 224 Gbps. Recent real-world LiFi tests in offices and industrial environments in Estonia report speeds of 1 Gbps.

Electromagnetic smog

A network using light reduces electromagnetic smog. Right now, LiFi can achieve 1.1Gbps at 10 meters using a 5 mW single LED, drawing about the same power as Wi-Fi. It’s a light with a modulator that can be installed anywhere a light is installed, such as street lamps or refrigerators. It also makes sense in areas where RF interference is a serious issue, such as hospitals, operating rooms and cockpits.

Why now?

LiFi products are about to become available commercially. On 25 November 2015, pureLiFi and Lucibel announced production of the first off-the-shelf solution, the fully-industrialized LiFi luminaire.

The LiFi luminaire will be produced at Lucibel’s industrial site in Barentin France and will integrate pureLiFi’s technology into a Lucibel LED lighting luminaire. Product is expected to roll out by Q3 2016.

The first LiFi luminaire installation will be at the Sogeprom’s headquarters in La Defense in Paris. Sogeprom, a subsidiary of Societe Generale and a major property developer, is looking at LiFi to provide the next generation of wireless connectivity for their customers.

For more information, see Prof Haas’ TEDGlobal 2011 presentation  “Wireless data from every light bulb”

Another Prof Haas’ presentation is “My Li-Fi Revolution”.

More Prof Haas videos.