Li-Fi

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. 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.

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 theUniversity of Edinburgh in the UK. The D-Light project at Edinburgh's Institute for Digital Communications was funded from January 2010 to January 2012. Has 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.

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.A number of companies offer uni-directional VLC products.

VLC technology was exhibited in 2012 using Li-Fi. 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.

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.

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.

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.

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