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04/07/2023 visible light communication
VISIBLE LIGHT COMMUNICATION
04/07/2023 visible light communication
Waves for Wireless Communications
Low frequency (long wave length)
Radio wave InfraredVisible Light Ultraviolet
High frequency (short wave length)
04/07/2023 visible light communication
What is VLC ? Visible light communication (VLC)
uses rapid pulses of light to transmit information wirelessly
Transmitting data through light rather than radio signals is called LI-FI
Visible light communication (VLC) is a data communications medium using visible light between 400 THz (780 nm) and 800 THz (375 nm)
04/07/2023 visible light communication
History of Visible Light Communications
Photophone by Graham Bell in 1880
04/07/2023 visible light communication
The first experiment of Visible Light Communications wasdone by Graham Bell whose system was called Photophone.He loved the idea.This picture is from the website of Bell Laboratories whoseexperiment showed 200m distance voice communication.
04/07/2023 visible light communication
advantages These systems present advantages
over traditional UHF RF-based systems from improved isolation between systems, the size and cost of receivers/transmitters, RF licensing laws and by combining space lighting and communication into the same system
Relatively Cheaper Visible Light is non injurious to human
health
04/07/2023 visible light communication
How it works ?if the LED is on, you transmit a digital
1, if it's off you transmit a 0It is possible to encode data in the
light by varying the rate at which the LEDs flicker on and off to give different strings of 1s and 0s. The LED intensity is modulated so rapidly that human eyes cannot notice, so the output appears constant.
04/07/2023 visible light communication
Equipment neededHere Transmitter is a high
brightness LEDFor this ordinary Lighting
systems should be replaced with high brightness LED’s
Receiver is an array of photo sensors (nothing but a camera available in mobile phone)
04/07/2023 visible light communication
Technical description
To know in detail about VLC we need the following basics
VLC link configurationVLC transmitterVLC receiverBrightness control of LEDs
04/07/2023 visible light communication
VLC link configuration
It is of 4 types
1.Directed LOS2.Non-directed LOS3.Directed non-LOS4.Non-directed non-LOS
04/07/2023 visible light communication
VLC transmitter and receiver
Note : CDR=Clock and Data Recovery
04/07/2023 visible light communication
Wave length issuesThe transmitting LED is operating
at a wavelength of 380nm-480nmThe photo diode operates at a
wavelength of 400nm-1200nmThere are many photodiodes
whose bandwidths are over 200 MHz and is much wider than the VLC LED transmitter.
04/07/2023 visible light communication
InfrastructureMono-functional infrastructureMulti-functional infrastructure
•Road is a typical multi-functional one.•Telephone network is also multi-functional.•Most of infrastructures are multi-functional.•Lighting is now a mono-functional infrastructure.It will become multi-functional.
04/07/2023 visible light communication
Transmitting and receiving issuesBrightness control is the key issue of
transmitting distanceHere the Network interface module can
be compared with a wireless modemThe receiver should be equipped with
an optical concentrator to get transmitted data accurately
Clock and data recovery circuit is inserted to achieve synchronization between input and output
04/07/2023 visible light communication
Image sensor communication
Photo diode without lens is a simple andeconomical detection method. However, its communication distance is limited short due to background lights.
Brightness control of LEDAM dimming is the way of LED
dimming which controls the DC forward current injected into the LED. By changing the DC forward current, the emitted luminous flux is controlled.
It is very simple to implement, but it could cause a change of the chromaticity coordinates of the emitted light.
04/07/2023 visible light communication
Losses during transmission
As we are using light for data transmission we may get interferences of unwanted light
To avoid these errors we need an optical concentrator
04/07/2023 visible light communication
Future applications of VLCLight-Fidelity is a killer
application of Wi-Fi ,using Li-Fi we can use our everyday LED light as a transmitter
Under water data transmission is also possible with VLC
04/07/2023 visible light communication
Conclusions• Infrastructure is important to realizeubiquitous communications.• Lighting will become a multi-functionalinfrastructure whose second function isvisible light communication.• VLC does not ruin the room design and landscape.• VLC is easy for handicapper people.• Image sensor communication isfor long distance VLC.
04/07/2023 visible light communication
Thank you
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