Wireless communication using off-the-shelf room lights is attracting researchers like moths to a flame
Room lighting could be used to offer an alternative to radio waves for wireless communications. There are several organisations around the world working on using LED lighting to provide Li-Fi, a competitor for Wi-Fi.
Harald Haas, a professor at the University of Edinburgh, coined the term Li-Fi. During a demonstration of his system, he said, “It’s impressive when you consider how many light sources are all around us. We have before our eyes the solution for transferring large amounts of data. With the aid of light we can contribute significantly to the expansion of wireless networking.”
Old Light Through New Windows
The idea behind visible light communications (VLC) pre-dates radio transmissions and has existed for over a century. Alexander Graham Bell, who was born in Edinburgh, used modulated sunlight to send a wireless phone message in 1880 using an invention he called the Photophone.
Using LEDs, Haas has managed to reach speeds of 100Mbps (Mbits per second), somewhat less than a Japanese competitor, Outstanding Technology, which has a similar system peaking at 160Mbps. Even the Japanese achievement is a standstill speed compared to a Fraunhofer Institute for Telecommunications team in Germany, sponsored by Siemens, that holds the VLC record at 800Mbps but considers 500Mbps to be more sustainable. To achieve these speeds, the team used an Ostar LED, one of the brightest LEDs on the market, and one that can match the required modulation speeds.
The Edinburgh effort is pushing ahead and Haas’ team hopes to match the German effort by the end of this year using more conventional household LEDs.
LED lights have taken over from fluorescent lights as the transmission source because they are now starting to proliferate and analysts predict that prices will begin to drop from the current level of £20-£30 to something more attractive. The bulbs house arrays of LEDs to give the kind of luminescence required for room lighting and the colour of the light can be controlled.
These properties have opened the way to calling them smart lights. It could be feasible in future to pass several signals using different wavebands of light. In fact, one of the requirements that is being investigated is the desire to switch the low-energy lights off at the end of the day, or on bright sunny days. Research is already being done at the infrared end of the spectrum for dark light communications.
The applications appear to be there and several have been touted. The system could be an alternative public network used in airports and other areas where radio transmissions are kept to a minimum. It could also be used in domestic and business situations where radio cannot penetrate thick walls or traverse areas of high electrical activity. The signals can also be passed through water where line of sight is no problem.
Using room lighting as a transmitter is an improvement over current infra-red systems that require special transmitters. The electric cabling powering the bulb can be used to transmit the signals and the light transmission can form the final hop to the device – which could be a computer, television or any other intelligent household or office equipment. Using ceiling lighting also has the advantage of offering a clear line of sight viewpoint on most parts of a room.
The light can also be shaded to enhance security and prevent the kind of “street leakage” that occurs when Wi-Fi signals project to the outside of a building.
VLC is a maturing technology but it could be over five years before it is ready for market.