light fidelity (VLC) (LiFi)
Light Fidelity (LiFi) is a concept in which data is transmitted over short distances using modulated visible light. This concept is also known as Visible Light Communication( VLC). However, the term LiFi for Light Fidelity is likely to prevail.
LiFi technology transmits data in the visible wavelength range between 375 nm and 750 nm.or in the near- infrared range between 750 nm and 1500 nm. Light is emitted using VCSEL lasers or high- power LEDs from ceiling lights or wall lights as transmitting devices and photodiodes as receiving devices that demodulate the received light. Transmitting devices and receiving devices in a line of sight are stationary. However, the light signals can also be reflected from ceilings and walls and received by the receiving devices without a line of sight being present.
Transmission through walls or fixtures is not possible. With good alignment of the light transmission, high data rates can be transmitted with LiFi. These are dependent on the signal source. Data rates of 5 Gbit/s are achieved with light-emitting diodes, micro-LEDs achieve 10 Gbit/s and laser diodes 100 Gbit/s. Data rates between 1 Gbit/s and 6 Gbit/s are standardized.
LiFi can also be used where radio signals could cause problems due to electromagnetic compatibility. The concept supports point-to-point( P2P), point-to-multipoint( P2MP) and multipoint-to-multipoint links.
In research facilities, LiFi has been used to achieve data rates of well over one hundred gigabits per second. In practice, data rates of up to 1 Gbps are achieved, limited by the opto-electronic components used for light modulation and demodulation.
LiFi is being worked on by several standardization bodies. For example, by IEEE 802.15.7, by the ITU-T in Recommendation G.VLC, and by the IEEE project groups 802.15.13 and 802.11bb.