July 28, 2011

Besides saving energy a switch to LED lights can be used to enable gigabit per second Li-Fi that can be ten times cheaper than Wi-Fi

Siemens researchers have improved on their own record for wireless data transfer using white LED light. (back in 2010) In collaboration with the Heinrich Hertz Institute in Berlin, they have achieved a data transfer rate of up to 500 megabits per second (Mbit/s), significantly bettering the previous record of 200 Mbit/s. Wireless data transport by means of light paves the way for new applications in the home as well as in industry and transportation.

* The researchers used an Ostar LED, one of the brightest LEDs on the market, which can be modulated at such a frequency that data transfer rates of up to 500 Mbit/s are possible.

* The resulting changes in brightness remain imperceptible to the human eye. The receiver is a photodetector which converts the light signals into electrical pulses.

* Known as VLC (Visible Light Communication), this form of data transfer has a variety of potential applications.

New Scientist -
"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.



In the home, for example, it could represent a valuable addition to established WLAN technology. Increasingly, wireless networks are compromised by the fact that in many buildings the three independent WLAN frequency bands are multiply occupied, which leads to collisions among the data packets. In a situation like this, visible light, as a currently unused and license-free medium, offers a suitable alternative. A further advantage is that this form of data transfer is impervious to interception. Only the photodetector that is positioned directly within the light cone is able receive the data. In other words, it is impossible to "tap" the data transported in the light beam.

Europe has the OMEGA : Home gigabit access project

Gigabit Home Access Networks are a pivotal technology to be developed if the EU Vision of the Future Internet is to be realised. Consumers will require such HANs to be simple to install, without any new wires, and easy enough to use so that information services running on the HAN will be just another utility, as, for instance, electricity, water and gas are today.

The OMEGA HAN is centered round the needs of the user: gigabit RF and optical links, combined with more robust wide-area RF and visible-light communications will provide wireless connectivity within and the home and its surroundings. Combined with power-line communications this provides a home backbone without new wires. A technology-independent MAC layer will control this network and provide services as well as connectivity to any number of devices the user wishes to connect to it in any room in a house/apartment, and further, this MAC layer will allow the service to follow the user from device to device.

In order to make this vision come true, substantial progress is required in the fields of optical-wireless and RF physical layers, in protocol design, and in systems architectures.

42 page presentation, Visible light communications: achieving high data rates (Feb, 2011)

VLC: Increasing information rate
- Channel
Bandwidth limited by LED (~10s of MHz)
Very high signal to noise ratio

- Increasing information rate
Complex modulation
Equalisation
Parallel (MIMO) communication

- Other considerations
Dimming and control


- High data rates definitely feasible
100s-1000s Mbit/s using ‘normal to bright’ levels of illumination

- Challenges
Technological
Modification of sources to make it easier
Providing an uplink
Dimming
Efficiency penalties

- Other
‘It’s not our channel’ problem
How to integrate them in the wireless infrastructure
‘Careful use of photons’

Ultra high frequency power line communication transmission could provide the uplink from fiber to the home. Fiber to the home and fiber to the building at high transmission speeds exists in South Korea, Hong Kong, parts of Japan and some northern European countries.

Even Higher information rate transmissions over power line use RF through microwave frequencies transmitted via a transverse mode surface wave propagation mechanism that requires only a single conductor. An implementation of this technology is marketed as E-Line. These systems claim symmetric and full duplex communication in excess of 1 Gbit/s in each direction. Multiple Wi-Fi channels with simultaneous analog television in the 2.4 and 5.3 GHz unlicensed bands have been demonstrated operating over a single medium voltage line conductor. Because the underlying propagation mode is extremely broadband (in the technical sense), it can operate anywhere in the 20 MHz - 20 GHz region. Also since it is not restricted to below 80 MHz, as is the case for high-frequency BPL, these systems can avoid the interference issues associated with use of shared spectrum with other licensed or unlicensed services.
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