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