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Li-Fi

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Li-Fi refers to wireless communication systems using light as a medium instead of traditional radio frequencies, as in technology using the trademark Wi-Fi.[1] Li-Fi has the advantage of being able to be used in electromagnetic sensitive areas such as in aircraft or nuclear power plants, without causing interference. However, the light waves used cannot penetrate walls which makes Li-Fi more secure relative to Wi-Fi.[2][3]

History

The general term visible light communication (VLC), includes any use of the visible light portion of the electromagnetic spectrum to transmit information. The term Li-Fi was coined by Harald Haas from the University of Edinburgh in the UK. The D-Light project at Edinburgh's Institute for Digital Communications was funded from January 2010 to January 2012.[4] Hass promoted this technology in his 2011 TED Global talk and helped start a company to market it.[5] PureVLC is an original equipment manufacturer (OEM) firm set up to commercialize Li-Fi products for integration with existing LED-lighting systems.[6][7]

In October 2011, companies and industry groups formed the Li-Fi Consortium, to promote high-speed optical wireless systems and to overcome the limited amount of radio-based wireless spectrum available by exploiting a completely different part of the electromagnetic spectrum.[8] A number of companies offer uni-directional VLC products.

VLC technology was exhibited in 2012 using Li-Fi.[9] By August 2013, data rates of over 1.6 Gbps were demonstrated over a single color LED.[10] In September 2013, a press release said that Li-Fi, or VLC systems in general, do not require line-of-sight conditions.[11] In October 2013, it was reported Chinese manufacturers were working on Li-Fi development kits.[12]

VLC communication is modeled after communication protocols established by the IEEE 802 workgroup. This standard defines the physical layer (PHY) and media access control (MAC) layer. The standard is able to deliver enough data rates to transmit audio, video and multimedia services. It takes count of the optical transmission mobility, its compatibility with artificial lighting present in infrastructures, the defiance which may be caused by interference generated by the ambient lighting. The MAC layer allows to use the link with the other layers like the TCP/IP protocol.[citation needed]

The standard defines three PHY layers with different rates:

  • The PHY I was established for outdoor application and works from 11.67 kbit/s to 267.6 kbit/s.
  • The PHY II layer allows to reach data rates from 1.25 Mbit/s to 96 Mbit/s.
  • The PHY III is used for many emissions sources with a particular modulation method called color shift keying (CSK). PHY III can deliver rates from 12 Mbit/s to 96 Mbit/s.[13]

The modulations formats preconized for PHY I and PHY II are the coding on-off keying (OOK) and variable pulse position modulation (VPPM). The Manchester coding used for the PHY I and PHY II layers include the clock inside the transmitted data by representing a logic 0 with an OOK symbol "01" and a logic 1 with an OOK symbol "10", all with a DC component. The DC component avoids the light extinction in case of an extended line of logic 0.[citation needed]

Optical orthogonal frequency-division multiplexing (O-OFDM) modulation methods were modeled for data rates, multiple-access and energy efficiency.[14]

See also

References

  1. ^ Condliffe, Jamie (28 July 2011). "Will Li-Fi be the new Wi-Fi?". New Scientist.
  2. ^ Li-Fi – Internet at the Speed of Light, by Ian Lim, the gadgeteer, dated 29 August 2011.
  3. ^ "Visible-light communication: Tripping the light fantastic: A fast and cheap optical version of Wi-Fi is coming". The Economist. 28 January 2012. Retrieved 22 October 2013.
  4. ^ Povey, Gordon. "About Visible Light Communications". pureVLC. Archived from the original on 18 August 2013. Retrieved 22 October 2013. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  5. ^ Haas, Harald (July 2011). "Wireless data from every light bulb". TED Global. Edinburgh, Scotland.
  6. ^ "pureVLC Ltd". Enterprise showcase. University of Edinburgh. Retrieved 22 October 2013.
  7. ^ Tony Smith (24 May 2012). "WTF is... Li-Fi? Optical data transfer's new leading light?". The Register. Retrieved 22 October 2013.
  8. ^ Povey, Gordon (19 October 2011). "Li-Fi Consortium is Launched". D-Light Project. Archived from the original on 18 August 2013. Retrieved 22 October 2013. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  9. ^ Watts, Michael (31 January 2012). "Meet Li-Fi, the LED-based alternative to household Wi-Fi". Wired Magazine.
  10. ^ pureVLC (6 August 2012). "pureVLC Demonstrates Li-Fi Streaming along with Research Supporting World's Fastest Li-Fi Speeds up to 6 Gbps". Press release. Edinburgh. Retrieved 22 October 2013.
  11. ^ pureVLC (10 September 2013). "pureVLC Demonstrates Li-Fi Using Reflected Light". Edinburgh. Retrieved 22 October 2013.
  12. ^ Iain Thomson (18 October 2013). "Forget Wi-Fi, boffins get 150Mbps Li-Fi connection from a lightbulb: Many (Chinese) hands make light work". The Register. Retrieved 22 October 2013.
  13. ^ An IEEE Standard for Visible Light Communications visiblelightcomm.com, dated April 2011.
  14. ^ Tsonev, D.; Sinanovic, S.; Haas, Harald (15 September 2013). "Complete Modeling of Nonlinear Distortion in OFDM-Based Optical Wireless Communication". IEEE Journal of Lightwave Technology. 31 (18): 3064–3076. doi:10.1109/JLT.2013.2278675.
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