In this video Harald describes how they have developed digital modulation techniques that enable off-the-shelf LED light bulbs to transmit data wirelessly faster than a typical WLAN access point.
Visible light communications (VLC) refers to methods of high speed wireless communication using the visible wavelengths of the electromagnetic spectrum.
This currently involves the use of general purpose light emitting diode (LED) luminaires for simultaneous illumination and data transmission. VLC works by rapidly varying (i.e., modulating) the intensity of the emitted light – commonly referred to as intensity modulation. While this can be detected by specially designed optical receiver devices – using a method called direct detection, it is imperceptible to the human eye.
With more than 1.4million cellular base stations and 5 billion mobile phones in use around the world, mobile broadband is an essential part of modern life – easily comparable to electricity and clean water supply. Together, these devices already produce about 600 terabytes of data (about 128,000 DVDs) every month – and that number is expected to grow exponentially over time. As a result, there is a looming problem of capacity. There is very little free radio frequency (RF) spectrum and the demand is rapidly outstripping the supply. Additionally, any new RF spectrum must be licensed before use and that is a very expensive process.
There is also the problem of efficiency: the 1.4 million base stations deployed around the world consume about 2 Gigawatts of power at maximum capacity – equivalent to the output of a large nuclear power plant – of which only about 5% is directly used for communication while the rest is used for cooling. Electromagnetic interference (EMI) is yet another issue that limits the use of RF wireless systems in sensitive areas such as aircraft and hospitals.
Security is another cause for concern with radio based wireless communication systems – it is very difficult to keep out eavesdroppers and unauthorised receivers since RF signals cannot be easily contained and/or directed. In contrast, VLC is safe, cheap, secure and green.
Light is all around us – it is a natural part of life – and as such there are no health concerns associated with its use as a communications medium. Since it does not cause EMI, it can be also used in intrinsically safe environments such as aircraft cabins, oil & gas platforms and hospitals. The visible light spectrum is also plentiful (about 10,000 times larger than RF) and does not currently require a license for use.
Furthermore, the devices are simpler and therefore cheaper to produce compared their RF counterparts. These features make VLC an attractive option for RF spectrum relief and dedicated use. The optical nature of the technology has an interesting security implication – it is easy to simply point the transmitter at an intended receiver and make it impossible for a concealed eavesdropper to detect the transmission.
Finally, The green credential of VLC is linked with the high efficiency of LED based lighting. The data is piggybacked on the illumination provided by the LED and this requires little extra energy. With LED luminaires already replacing inefficient incandescent and fluorescent lighting in homes and offices around the world, this represents a tremendous opportunity for VLC.
Research collaboration with Prof. Nigel Topham (Informatics) – EPSRC Grant EP/I013539/1
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