Turning to light for wireless communication
Recently I noticed an article in the IEEE Computer publication which caught my interest in the subject of lights for wireless communication. The author, Lee Garber, made the point that in search for better ways to transmit data, researchers have turned to the use of visible light (VLC).
Of course the concept is not new; it has been around for more than 130 years. During the Boer War the mainstay of communication was the heliograph, as the radio equipment ordered from Siemens by President Kruger was confiscated in Cape Town and never reached the Transvaal.
The Heliograph can probably be traced back to Roman times. It operates by reflecting the sun’s rays from an adjustable mirror to another point where the message is read. By moving the mirrored table it is possible to send messages long distances using the Morse code system of dots and dashes.
The instrument reached its peak efficiency during the Anglo Boer War, with speeds of up to 16 words per minute. Depending on the size of the mirror, the heliograph had a range of nearly 160 km.
There are many stories around the use of the heliograph, including this classic: “On one occasion the only recipient of a British heliograph message was a Boer heliograph team. They flashed back, “Will be with you tomorrow”. The British reply is not repeatable!”
Heliographs were used during the first and second world wars, and the last recorded use of the heliograph under active service conditions was in 1941, at the siege of Sollum Hayata in the Western Desert.
Heliograph diagram
The modern VLC uses modulated light signals rather than radio frequencies or other types of signals to transmit data. VLC technology could be utilised as internet access and various types of networking as well as point-to-point and point-to-multipoint communications. Researches working on VLC say that it offers important advantages over current wireless systems including higher data rates, better security and there is more spectrum available.
VLC systems can work with either a single light source of a specific colour or by combining red, green and blue light sources to produce the desired colour.
Some interesting research is being carried out at the University of Edinburgh. Prof Harold Haas has been working on VLC since 2004. He and his colleagues call their project D-Light (data light) and Li-Fi (Light Fidelity.) Haas expects his technology will be useful for purposes such as internet access, vehicle-to-vehicle communications, and machine-to-machine communication. He and his team are now planning to start a spin-off company.
Another research initiative financed by the EU was an interdisciplinary project involving both industry and academia. Named Omega, the project ran from 2008 till March 2011. The main objective was to develop a user-friendly high bandwidth home network.
Omega’s demonstration used 16 high power ceiling-mounted LEDs. The output from four video players was aggregated into an Ethernet stream and modulated into an electrical current sent to the LEDs. The LEDs then continuously broadcasted four high definition videos at 100 Mbits per seconds.
One of the problems the Omega team encountered was to integrate the VLC lights with ordinary lighting. Just think of the possibility; switch on LED lights in your home or office and you have an instant connection to the internet, home or office data network.
Unfortunately there are still many problems to be solved – the main one appears to be cost.
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