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VISIBLE LIGHT COMMUNICATION

Report of TERM PAPER I (MECS-657) submitted in partial fulfillment of the

requirement for the degree of

Master of Technology

In

Computer Science & Engineering

(Regular)

Under the supervision of By:-

Dr. Amit Prakash Singh Siddharth Jhumat

Enroll. No. 01016404812

UNIVERSITY SCHOOL OF INFORMATION AND COMMUNICATION

TECHNOLOGY

GURU GOBIND SINGH INDRAPRASTHA UNIVERSITY

DWARKA, DELHI – 110075

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CERTIFICATE

This is to certify that the TERM PAPER 1 entitled “VISIBLE LIGHT

COMMUNICATION” submitted by SIDDHARTH JHUMAT to the

University School of Information and Communication Technology (Guru

Gobind Singh Indraprastha University), Delhi in partial fulfillment for

the award of Degree of Master of Technology in Computer Science &

Engineering is a record of bonafide work carried out by him under my

supervision during the year 2012-2013.

Dr. Amit Prakash Singh Siddharth Jhumat USICT, Guru Gobind Singh Indraprastha University Enroll. No. 01016404812

Dwarka, Delhi – 75

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Table of Contents

Abstract …………………………………………………………………………………………………………….. 1

Introduction ………………………………………………………………………………………………………. 1

RONJA………………………………………………………………………………………………………………… 2

Process of sending and receiving data via visible light………………………………………… 4

LED(Light Emitting Diode)…………………………………………………………………………………… 4

Li-Fi Technology…………………………………………………………………………………………………..7

Transmit Data Using Visible Light ………………………………………………………………………10

Characteristics of VLC…………………………………………………………………………………………11

VLC vs RF Communication…………………………………………………………………………………..11

VLC vs IR communication……………………………………………………………………….…………..11

Data Transmission………………………………………………………………………………………………12

Li-Fi Development Kit(LDK)..……………………………………………………………………………….14

Li-Fi Consortium …………………………………………………………………………………………………15

IEEE 802.15 WPAN TG7 ……………………………………………………………………………………..18

Visible Light Communications Consortium………………………………………………………….18

Transmitter Circuit …………………………………………………………………………………………….19

Receiver Circuit…………………………………………………………………………………………………..20

VL road to vehicle communication using high speed camera …………………………….21

VLC link for audio and video transmission ………………………………………………………….22

Indoor Positioning by LED VLC and image sensors………………………………………………22

Difficulties ………………………………………………………………………………………………………….23

Conclusion …………………………………………………………………………………………………………23

Abbreviations …………………………………………………………………………………………………….24

References ……………………………………………………………………………………………………… 24

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Visible Light Communication

Siddharth Jhumat

Enrollment Number: 01016404812

M.Tech (Computer Science & Engineering)-REGULAR

University School of Information and Communication Technology

Abstract

The Visible light communication

(VLC) is a communication technology

which uses visible light as optical carrier

for data transmission and illumination.

Visible light is free. No company owns

property rights for visible light and thus

no royalty fees have to be paid nor does

expensive patent-license have to be

purchased in order to use visible light

for communication purposes [1]. VLC

offers a real alternatives to radio based

communications since the spectrum is

free, plentiful, and the cost of

implementation is actually less than

equivalent radio technology. Our

wireless technology is based on radio

waves which are limited, scarce and

expensive [2]. The visible light spectrum

is 10,000 times larger than the radio

frequency spectrum. The prime function

of LEDs is to provide illumination.

Compared to traditional light sources,

LEDs have the advantages of long life

expectancy, high lighting efficiency, easy

maintenance and environmental

friendliness. VLC is harmless for our

health as well as our daily

circumstances. In this term paper, I will

study how visible light can be used in

communication purpose, its advantages

and disadvantages in day to day life and

how to overcome such disadvantages to

make it a success.

Introduction

Radio Waves extend from 3 kHz

to 300 GHz. They are used in mobile

communication, radio communication,

communication satellites and other

navigation systems. The radio frequency

spectrum is a limited natural resource.

Some of its limitations are:

a. Different radio frequencies

have different propagation

characteristics. Lower frequencies

can propagate over large

distances and higher frequencies

propagate over small distances.

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b. Radio frequency propagation

does not obey political

boundaries of different countries.

Because of this nature of

propagation, the RF spectrum has

to be shared among different

nations. So the rules governing

the use of RF spectrum is

international in character.

c. Different manufacturers produce

equipment in the frequency

bands most commonly used at

the global level.

Visible spectrum has a frequency of 400-

790 THz [3]. The visible spectrum is the

portion of the electromagnetic spectrum

visible to the human eye. Many species

can see light with frequencies outside

the visible spectrum for e.g. bees.

RONJA (Reasonable Optical Near

Joint Access)

Ronja is an optoelectronic device

you can mount on your house and

connect your PC, home or office

network with other networks [4]. Or you

can use it as a general purpose wireless

link for building any other networking

project. The device has 1.4 km range

and has stable 10 Mbps full duplex data

rate. One Ronja device is a single long-

distance optical transceiver that is

capable of running against the same or

compatible device on the other side of

the link. The topology is point-to-point.

The material costs are very low, about

100 USD. The operation is immune to

interference and quite reliable -

interrupted only by dense fog.

Limitation

For transmission, we need clear

visibility between the transmitter and

receiver. If by any chance the beam is

obscured, the link stops working.

Problems may occur during conditions

of snow and dense fog. So proper care

need to be taken in cold countries in the

working of RONJA.

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RONJA INSTALLATION OVERVIEW

RONJA ELECTRONICS OVERVIEW

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Process of sending and receiving data

via visible light

VLC is mostly used indoors and

transmitted light consequently does not

leave the room when the doors are

closed and curtains drawn, because light

cannot penetrate solid objects such as

walls and furniture. Therefore, it is hard

to eavesdrop on a visible light based

conversation, which makes VLC a safe

technology if the sender intends to

transfer confidential data.

The most important requirement

that a light source has to meet in order

to serve communication purposes is the

ability to be switched on and off again in

very short intervals, because this is how

data is later modulated. This rules out

many conventional light sources, such as

incandescent lamp.

In Visible light communication,

data is modulated on the light source

using modulation techniques like pulse

position modulation or frequency shift

keying. In the receiver end

demodulation is performed using pulse

position modulation technique to fetch

the data back from the light source. So it

is shown as a six step process – Sender

Data, Modulation, Light Source, CMOS,

Demodulation, and Received Data.

LED (Light Emitting Diode)

By utilizing the advantage of fast

switching characteristics of LED’s

compared with the conventional

lightning, the LED illumination is used as

a communication source. Since the

illumination exists everywhere, it is

expected that the LED illumination

device will act as a lighting device

and a communication transmitter

simultaneously everywhere in a near

future.

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LED’s are used in two propagation paths

[5]:

1. Line of sight (LOS): Strong paths

are calculated using the

illumination patterns of LED

arrays.

2. Diffuse: Modeled by assuming the

room is equivalent to an

Integrating sphere.

There are two types of visible

wavelength LED’s [6]:

1. Single color LED – for example

Red (R), Green (G) and Blue (B)

LED.

2. White LED – Uses phosphorous

for converting the emission

wavelength from the original

active area.

Typically, red, green, and blue LEDs emit

a band of spectrum, depending on the

material system. Red LEDs emits the

wavelength around 625 nm, green LEDs

around 525 nm, and blue LEDs around

470 nm. The white LED draws much

attention for the illumination devices.

Comparing the LED illumination with the

conventional illumination such as

fluorescent lamps and incandescent

bulbs, the LED illumination has many

advantages such as high-efficiency,

environment-friendly manufacturing,

design flexibility, long lifetime, and

better spectrum performance.

Most of white LEDs is comprised

of LED chip emitting short wavelength

and wavelength converter (for example,

phosphor). The short wavelength light

from the LED chip is absorbed by the

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phosphor and then the emitted light

from the phosphor experiences

wavelength shift to a longer wavelength.

As a result, the many wavelength

components are observed outside the

LED. A white light can be generated

from a blue LED with appropriate

phosphor. The emission spectrum of a

phosphor based LED has the strong

original blue spectrum and the longer

wavelengths shifted by the phosphor.

The basic LED consists of a

semiconductor diode chip mounted in

the reflector cup of a lead frame that is

connected to electrical (wire bond)

wires, and then encased in a solid epoxy

lens. LEDs emit light when energy levels

change in the semiconductor diode. This

shift in energy generates photons, some

of which are emitted as light. The

specific wavelength of the light depends

on the difference in energy levels as well

as the type of semiconductor material

used to form the LED chip. Solid-state

design allows LEDs to withstand shock,

vibration, frequent switching (electrical

on and off shock) and environmental

(mechanical shocks) extremes without

compromising their famous long life

typically 100,000 hours or more. Unlike

incandescent bulbs that give off the full

spectrum of light in a spherical pattern,

LED’s emit a single beam of focused

wavelength (color) in only one direction,

in a variety of angles. While LEDs deliver

100 percent of their energy as colored

light, incandescent bulbs waste 90

percent or more of their energy in light

blocked by the colored lens or filter.

Incandescent bulbs also waste 80

percent to 90 percent of their energy on

heat generation to reach the

temperature for which (Kelvin scale)

they are designed.

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Li-Fi Technology

Among the many new gadgets unveiled at the recent Consumer Electronics Show in Las Vegas was a pair of smart phones able to exchange data using light. These phones, as yet only prototypes from Casio, a Japanese firm, transmit digital signals by varying the intensity of the light given off from their screens. The flickering is so slight that it is imperceptible to the human eye, but the camera on another phone can detect it at a distance of up to ten meters. In fact, they are the beginning of a fast and cheap wireless-communication system.

The data being exchanged by

Casio's phones were messages. But the

firm sees bigger applications, such as

pointing a smart phone at an illuminated

shop sign to read information being

transmitted by the light: opening times,

for example, or the latest bargains.

As radio-based wireless is found

everywhere, more and more devices

transmitting more and more data are

able to connect to the internet, either

through the mobile-phone network or

through Wi-Fi. But there is only a limited

amount of radio spectrum available.

Using light offers the possibility of

breaking out of this conundrum by

exploiting a completely different part of

the electromagnetic spectrum, one that

is already present because it is used for

another purpose: illumination.

The rate of data transfer is also

good. Dr Povey's group is already up to

130 megabits a second (faster than

some older Wi-Fi routers) over a

distance of about two metres, using

standard LEDs. Dr Povey, who is also the

boss of VLC, a firm set up to

commercialise the technology, thinks

such devices should be able to reach 1

gigabit per second (Gbps), and do so

over greater range. Specially

constructed LEDs would be even faster.

The Li-Fi consortium reckons more than

10 Gbps is possible. In theory, that

would allow a high-definition film to be

downloaded in 30 seconds.

A big advantage of light is that it

can be used in areas which contain

sensitive equipment that radio signals

might interfere with, such as aircraft and

operating theatres. LEDs in the ceiling of

Light Signal

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an airliner would not only allow internet

access but could also transmit films on

demand to individual seats, removing

the need for lots of expensive and heavy

cabling, thus saving airlines fuel.

There are limitations to using

light, of course. Unlike radio, light waves

will not penetrate walls. Yet for secure

applications that could be a bonus. And

light bulbs—some 14 billion of them

around the world—are almost

everywhere and often on. As they are

gradually replaced by LEDs, every home,

office, public building and even

streetlight could become a Li-Fi hotspot.

VLCC (Visible Light Communication

Consortium), established in 2003 and

supported by major Japanese companies

such as NEC, Toshiba, Sony and

Panasonic Electric Works as well as the

Japanese unit of Samsung, is developing

standards for visible light

communications using a combination of

white LED lamps and receivers such as

photodiodes and image sensors. With

the collaboration of IrDA (Infrared Data

Association), the many mobile phones

with infrared communication capability

will work as receivers. Today's devices

almost always use RF-based solutions

such as WLAN or Bluetooth to

communicate wirelessly. Those solutions

support up to some hundred Mbit/s

data rate. Currently, that is no longer

sufficient for many applications and

large file transfers. With this in mind,

Fraunhofer Institute for Photonic

Microsystems (IPMS), Dresden, has

developed an optical wireless

communication (OWC) link with up to 3

Gbit/s data rate. This can be used for

docking solutions or to replace cable

connections such as USB or Gigabit

Ethernet.

Dr. Harald Haas and his team at the UK's

University of Edinburgh, are the brains

behind this new patented technology

that uses beams of flickering light to

transmit digital information wirelessly.

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"My big idea is to turn light bulbs into

broadband communication devices ... so

that they not only provide illumination,

but an essential utility," he says. Haas

claims that data can be sent by adding a

microchip to any humble LED bulb,

making it blink on and off at a

phenomenal speed, millions of times per

second. It's this capability that allows

LEDs to transmit data in a rapid stream

of binary code that, although invisible to

the naked eye, can then be detected by

a light-sensitive receiver. The

implication is that wherever you have a

light bulb -- and there are an estimated

14 billion of them worldwide -- you have

the potential for a wireless Internet

connection. In practice, it means that

any street lamp could double up as a

web hotspot. Less congestion means

greater bandwidth and Haas says

transmission rates using "Li-Fi" could be

as high as one gigabit a second --

meaning that downloads of high-

definition films could take less time than

sending a text. "We use what is already

there," he says. "The visible light

spectrum is unused, it's not regulated,

and we can communicate at very high

speeds."[7]

Problems Associated:-

"Of course one problem is that light

can't pass through objects, so if the

receiver is inadvertently blocked in any

way, then the signal will immediately cut

out," Thomas Kamalakis, a lecturer at

the Department of Informatics and

Telematics at the Harokopio University

of Athens says.

Mark Leeson, associate professor

at Warnick University’s School of

Engineering also foresees challenges.

“The question is how will my mobile

phone communicate back with the light

source?” Lennon asks.

Both are valid issues, Haas says,

but he has a simple workaround. "If the

light signal is blocked, or when you need

to use your device to send information --

you can seamlessly switch back over to

radio waves."VLC is not in competition

with Wi-Fi, he says, it is a complimentary

technology that should eventually help

free up much needed space within the

radio wave spectrum."We still need Wi-

Fi; we still need radio frequency cellular

systems. You can't have a light bulb that

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provides data to a high-speed moving

object or to provide data in a remote

area where there are trees and walls

and obstacles behind," he says. Haas

says it could transform air travel by

allowing overhead cabin lights to

connect mobiles and laptops in-flight; it

could also improve conditions for those

working underwater -- such as people

on oil rigs -- where radio waves cannot

penetrate; LED car lights could even

alert drivers when other vehicles are too

close.

Transmit data using visible light

While visible light data transmission has been available for some time, there hasn't yet been a widespread real world use for it. [8] Japanese firm Outstanding Technology is aiming to change that with the Commulight system, which uses visible light communications to send info to smart phones and tablets via a receiver.

The receiving device obtains the ID

emitted by the LED device enabling it to

download content relevant to the user

location.

The firm has designed this system

as an application for guiding visitors in

galleries and museums. For example,

when a user stands in front of the

exhibition, the smart phone can show a

guide to that exhibition. The system can

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also be used for stores in a shopping

mall or buildings and in several

important events. In shopping malls

coupons and discounts can be

transmitted using this technology.

Characteristics of VLC

1. Human Safety: VLC poses no health

hazard to human body [9]. Thus, the

transmission power can be kept high if

needed.

2. High Data Rates: VLC inherits high

data rates from optical communications.

Thus it can be used for very high speed

wireless communications.

3. Bandwidth: VLC exploits the visible

region of electromagnetic spectrum.

Thus it offers much larger frequency

band (300 THz) compared to that

available in RF communications (300

GHz).

4. Ubiquitous Nature: VLC uses the

already available visible light sources for

wireless communications, so it is

expected to become a ubiquitous

technology in near future.

5. Security: As VLC involves line of sight

communication, so it is impossible to tap

the communication without breaking

the link. So it offers very secure

communication and can be used in high

security military areas where RF

communication is prone to eaves

dropping.

6. Unlicensed Spectrum: As VLC uses the

visible region of electromagnetic

spectrum, so it is free of cost.

VLC vs RF Communication

1. Limited Transmission Power: Unlike

VLC, in RF communications, the electric

transmission power cannot be increased

beyond a prescribed level as it poses

serious health hazard for human body.

2. Regulated Spectrum: Due to radio

wave restriction, there is no room to use

more radio frequencies. In addition, the

use of radio spectrum is regulated.

3. Banned in Sensitive Areas: The radio

wave cannot be used in hospitals and

space stations because it adversely

affects the performance of precision

instruments. These radio wave problems

above are easily solved by use of the

visible light communications.

VLC vs IR Communication

Limited Data Rates: In IR communication

data rates cannot be increased beyond a

prescribed level as it poses serious

threat to human eyes. This can be

attributed to the high energy density

created by IrDA due to invisibility. The

eye safety problem can be solved using

visible light communications. As

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compared to IR communication, the

visible light communication is suitable to

human eyes in terms of visibility. The

system employs LED, which can be

transmitted by a few watts, a relatively

high energy for the use of lighting. This

means that the VLC is capable of

transmitting data at higher data rates.

The VLC data rate is dependent

on the LED’s modulation bandwidth and

the standardization on physical layer

specifications has not yet been

published. The transmission distance for

VLC is possible up to several meters due

to its illumination requirement. Since

the infrared communication is used for a

remote controller, the maximum

distance is 3 meters.

The accompanying graph [10]

depicts the true picture of the technical

evolution of LEDs. It shows that in a few

years, LEDs will outshine all other

technologies owing to a small cost/

brightness and a large brightness/power

ratio.

Data Transmission

Modulation is the process of

varying one or more properties of a

high-frequency periodic waveform,

called the carrier signal, with a

modulating signal which typically

contains information to be transmitted.

With respect to VLC, modulation

schemes are used to transfer the data

given as a sequence of 0s and 1s into a

series of light pulses. The two main

alternative modulation schemes are as

follows [1] :-

1. Sub-Carrier Pulse Position Modulation

(SC-kPPM) – In Sub-Carrier Pulse

Position Modulation, the data is

separated into groups of log k bits each

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and there is only a single pulse for each

group. This method is widely used for

optical communication systems such as

optic fiber and IR remote controls,

where efficiency is required and little or

no external interference occurs.

2. Frequency Shift Keying (FSK) –

Frequency-shift keying (FSK) is a

frequency modulation scheme in which

digital information is transmitted

through discrete frequency changes of a

carrier wave. Signal frequency

determines whether or not the currently

transferred bit is 0 or 1. Two distinct

values (0 and 1) are represented by two

distinct pulse frequencies. This form of

FSK is also referred to as binary FSK.

The wireless communications

industry is facing a spectrum crisis.

Cellular data is off-loaded to Wi-Fi and

now Wi-Fi networks are congested.

Hand-held devices are consuming high

bandwidth content and we often wish to

transfer this content from device to

device. We talk about the Internet of

Things where every device is

interconnected, but without more

bandwidth it will be impossible to

provide reliable communications to all

of these “things”. For short-range high

data-rate links, visible light

communications advantages come to

the fore. Direct modulation eliminates

the need for radio circuits, antenna

systems or complex receivers. Investing

in ever more complex radio schemes at

increasingly higher frequencies is

unnecessary when there is 10,000x

more visible light spectrum compared to

radio spectrum. With data densities of

1000x those of radio the performance of

VLC looks very favorable.

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Li-Fi Development Kit (LDK)

The Li-Fi Development Kit (LDK)

[11] enables lighting manufacturers to

add visible light Communications to

their products. There are two main

components:

1. VLC Ceiling Unit

2. VLC Desktop Unit

LED Driver : Provided by the light fixture

or driver manufacturer, it usually

powers the LED light fixture directly. In

the LDK the driver powers the VLC

Ceiling Unit instead which then varies

the current going to the light fixture.

LED Light Fixture: This is also provided

by the light fixture manufacturer or

reseller. The LDK is designed to work

with a wide range of fixture and driver

combinations.

VLC Ceiling Unit: The VLC Ceiling Unit

consists of an infra-red detector and

optics, along with a processing unit that

decodes the received signal and encodes

the transmitter data onto the current

supplied to the LED light fixture. The

unit is connected to the data network

via a standard Ethernet RJ45 port.

VLC Desktop Unit: The VLC Desktop Unit

contains the same VLC transceiver

module contained within the VLC Ceiling

Unit. It is equipped with an infra-red

emitter and visible light detector. This

unit connects to client devices.

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Client Device: The client device is linked

to the VLC Desktop Unit using USB, e.g.

Laptop Computer

Li-Fi Consortium

The Li-Fi consortium [12] is a non-profit organization, devoted to introduce optical wireless technology. The Li-Fi consortium’s charter members are a leading group of international technology companies and research institutions in optical communication technology. The group is based on a collectively developed concept and roadmap to establish a new wireless technology in the market, which exceeds the abilities and qualities of wireless RF technology.

The Li-Fi Consortium has several purposes:

1. Promote optical wireless communications up to the multi-gigabit range in all their implementations.

2. Inform potential implementers of the companies and resources available to help them achieve their product goals.

3. Create whole solutions in anticipation of customer needs.

4. Coordinate with standardization groups and other industry organizations to provide OEM customers with a complete ensemble of technical and marketing support.

In an initial approach, the Li-Fi

Consortium defined different types of

technology to provide secure, reliable

and ultra high-speed wireless

communication interfaces. Those are:

1. GigaSpeed technology

2. Optical mobility technology

3. Li-Fi environmental features

GigaSpeed technology:-

The Li-Fi Consortium offers the fastest wireless data transfer technology available. Their current solutions cover effective transmission rates of up to 10 Gbit/s, allowing a 2 hour HDTV film to be transferred within less than 30 seconds. Smaller files are transferred instantly.

a. GigaDock – It is a module that plugs into mobile device. It provides up to 10Gbit/s two way bus-like data transfer.

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b. GigaBeam – IR port in mobile device for fast bulk transfers. 10 Gbit/s wireless file transfers.

c. GigaShower – Ceiling unit used for broadcasting large volumes of data. IR receivers are plugged into mobile devices to accept the data.

d. GigaMimo – It is a ceiling unit that steers multiple beams. The beams can be used to track user movement.

Optical Mobility Technology:-

The mobility concept of the LiFi Consortium is based on state of the art optical receiver chip technology. Mobile devices do not depend on a line of sight connection between the mobile device and the optical router. New optical receiver chips will be able to read reflections, also of very weak signals. Its large dynamic range is the basic of our mobility technology. Therefore, a room needs only one or few communication points in order to connect mobile devices to the optical network. This opens for an entirely new approach in optical mobile communication, enabling the implementation of additional features to an optical local network.

a. Optical Mobile – It is having 3 communication channels (RF, mobile, GigaSpeed). Datatransfer and reception is at 10 Gbit/s. It is used as a mobile phone as well as house phone. It provides the fastest data transfer method of a mobile device.

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b. Optical Memo – It is an optical memory stick having GigaSpeed transceiver. It communicates with mobile within a range of 2 m.

c. Optical Router – It is a hard drive for data storage. It stores data and functions as router/server for Li-Fi. It transmits for mobile communication at 100 Mbit/s. It covers radius of 5 – 10 m.

d. Optical Room Connector – It connects data with Li-Fi cloud from one room to another. It transmits data at 100 Mbit/s between rooms.

Li-Fi environment:-

The concept of the Li-Fi cloud creates an environmental friendly, healthy and smart network environment. Here are the features that make it possible.

a. Multi Channel mobile phone features - Mobile phone technology combining optical and RF communication. It switches automatically into mobile optical mode within a Li Fi cloud.

b. Security Features - Each optical receiver chip has integrated motion detector function to monitor the Li-Fi cloud. It lets you answer the door bell from wherever you are, it lets you monitor each room individually from wherever you are positioned in house,

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it lets you address intruders through your TV or loudspeaker.

c. Smart Home Features – It can control energy use through smart phone, it can control electrical equipment through smart phone, it can control heating and air conditioning through smart phone

IEEE 802.15 WPAN TG7

VLC standardization efforts have

been taking place since 2008 within the

IEEE 802.15 working group, which is

charged with overseeing standards for

wireless personal area networks,

including body area networks (

interconnecting devices on and around

the human body) and smart grid

systems (networks of utility sensors).

VLZ specifications are developed within

the IEEE 802.15.7 task group. The IEEE

802.15.7 Visible Light Communication

Task Group has completed a PHY and

MAC standard for Visible Light

Communications (VLC). The task group’s

inaugural meeting was held during the

January 2009 interim.

The chairman of the task group is

Eun Tae Won. A great deal of emphasis

is being placed on optimizing the

specification so that it works well within

its particular constraints. For example,

VLC environments can be lossier than

wired environments, so more loss-

resilient coding schemes are being

employed.

Visible Light Communications

Consortium (VLCC)

The purpose of this consortium

[13] is to research, to develop, to plan

this high-speed, safe, ubiquitous tele-

communication system from Japan by

using it to communicate the waviness of

visible light using a visible light element

for the lighting, the signal, the lightning

notice, and the display, etc. as the

above-mentioned, to standardize, and

to spread it.

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Transmitter Circuit

The transmitter [14] side has a

voltage regulator, level shifter and the

LED driver circuit.

Voltage Regulator:-

The voltage regulator is for

supplying constant voltage to the

voltage shifter. It is needed because the

unregulated voltage coming from our

electricity provider can fluctuate greatly

depending on several factors, including

time of day and appliances powering on

and off. Using a voltage regulator

compensates for all these problems and

protects the MAX3222 level shifter.

MAX3222 Level Shifter:-

Nearly all digital circuits use a

consistent logic level for all internal

signals — however, that level varies

widely from one system to another. A

level shifter connects one digital circuit

that uses one logic level to another

digital circuit that uses another logic

level.

The MAX3222 transceiver is a

level shifter which takes the +/-12v

levels of RS-232 and converts them to 0

to 5V of TTL levels. The RS-232 interface

on the computer uses -3v to -12v logic 1

and +3 to +12v for logic 0. The

transmitter circuit, however, uses VCC

as a logic 1 and 0V as logic 0. MAX3222

is used to interface between the RS-232

and TTL variants. It takes +/- 12V from

RS-232and gives out 0 to 5V.

LED Driver Circuit:-

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The signal from MAX3222 is sent

to the transmitter driver circuit as

shown in figure. The transistor 2N4401

serves as a switch to control the LED to

turn ON and OFF. The LED will turn ON

for 5V and OFF for 0V from the PIN 13 of

MAX322.

Receiver Circuit

The transmitter side has a voltage

regulator, level shifter and the

photodiode driver circuit. The operation

of the voltage regulator is same as in

transmitter circuit.

MAX3222 Transceiver:-

The operation of the MAX3222 is similar

to the operation explained in the

transmitter circuit section in 4.7 with a

few changes. The output of the receiver

circuit is fed to the pin 12 (T1IN) and the

pin 15 (T1OUT).

Photodiode Driver Circuit:-

The capacitors C1, C2, C3 and C4 are the

smoothing capacitors connected across

the DC supply to act as a decoupling

capacitor. Sometimes, the power supply

supplies an AC signal superimposed (also

known as noise) on the DC power line.

Such a signal is undesirable for the

electronic circuits because they need

pure DC supplies. A decoupling capacitor

prevents the AC signal by decoupling it

from the power supply and giving the

pure regulated power supply to the

comparator. When the photodiode is

exposed to LED light, the voltage across

the photodiode changes accordingly

with the LED ON and OFF switching

causing the voltage change to the non-

inverting pin 7.

So to summarize this we say that

the voltage regulator supplies constant

voltage to the level shifter from the

power supply by maintaining constant

DC voltages and avoiding unwanted

24

spikes in current. The level shifter helps

to convert the high voltages of RS-232

(which are +/- 11V from the model

computer) to transmitter and receiver

circuit levels (which are 0 to +5V). The

electrical data from the computer is

converted into optical data using LEDs

and transmitted over light, the optical

data is captured by the receiver,

converted into electrical data by the

photodiode and sent it to the client

computer.

Visible light road to vehicle

communication using high speed

camera [15]

Road to vehicle communication

[15] is what helps drivers by providing

traffic information. In Japan, VICS, shows

traffic information on car navigation

display. Using camera as the receiver

means that information is obtained from

the intensity of the transmitter image

captured by the camera.

It shows the basic usage of LED as a

transmitter and CAMERA as a receiver.

In this model, they mounted a camera

before the front end of the car. The

camera is used as the information

receiver from traffic signal lights. The

advantage of using the camera is that

multiple data can be transmitted by the

LEDs and received by High-speed

cameras.

25

Visible Light communication link for

audio and video transmission[15]

A VLC system to transmit high

quality video and audio signal was

proposed and demonstrated by using

illumination LEDs. The analog video

signal was modulated by using an ultra

high speed comparator in the

transmitter. The analog signal was

converted from analog to digital. Both

the video and analog signals were

transmitted using the illumination LEDs

in the transmitter.

The photodiode at the receiver senses

the optical signals from the LEDs and is

converted into electrical signals. The

electrical signal is then amplified to

recover the digital signal and converted

back to an analog signal to video/ audio

out.

Indoor Positioning by LED visible light

communication and image sensors [16]

The lighting can be used as a visible light

ID system, which informs an exact

location (for example, A corner of Room

Number 123, ABC Building, etc). The

26

each light has a different ID, which

shows a different exact location. This

positioning system can be used even in

the underground subway station,

shopping mall etc, where GPS is not

accurately used. The system is also very

convenient for the emergency use

(Indoor Navigation System). This is used

inside hospitals, too

Difficulties

Even though VLC can lead to

many interesting applications, as shown

in the previous sections, the technology

is not entirely free of certain drawbacks

and difficulties.

First of all, to successfully

transmit data, there has to exist a line of

sight between sender and receiver,

because visible light cannot penetrate

solid items or objects.

A severe disadvantage of VLC in

the medical field is that it is sometimes

imperative during surgery to switch off

background illumination (in order to

view some monitors for instance). This

scenario is obviously incompatible with

VLC and it might perhaps never be used

in operating rooms.

Conditions such as fog and hazy

air also vastly hamper data transmission

via visible light. Moreover, reflections

might occur on mirroring surfaces which

can lead to receiving wrong data.

Conclusion

Visible Light Communication is a rapidly

growing segment of the field of

communication. VLC is a promising

technology with a wide field of

prospective applications. An ever-

growing interest in VLC throughout the

world can be expected to lead to real-

world applications in the future. In some

fields of application it poses a favorable

alternative to conventional solutions

(infrared, WLAN etc.). The main goals for

the future are increasing the

transmission rate and improving

standardization. There are many

advantages to using VLC. There are also

many challenges. VLC will be able to

solve many of the problems people have

been facing for many years, mainly

environmental and power usage issues.

VLC is still in its beginning stages, but

improvements are being made rapidly,

and soon this technology will be able to

be used in our daily lives.

27

Abbreviations

VLC – Visible Light Communication

LED – Light Emitting Diode

IEEE – Institute of electrical and

electronics engineers

WLAN – Wireless Local Area Network

GPS – Global Positioning System

DC – Direct Current

AC – Alternating Current

M.Tech – Master of Technology

RF – Radio Frequency

Li-Fi – Light Fidelity

PPM – Pulse Position Modulation

FSK – Frequency Shift Keying

VLCC – Visible light communication

consortium

WPAN – wireless personal area network.

IR – Infra Red

OWC – optical wireless communication

LOC – Line of Sight

Gbps – giga bits per second

References

*1+ Christian Pohlmann, “Visible Light

Communication”, June 2010.

[2] P.K.Garg, “RF Spectrum – A Precious Natural Resource and its Efficient Use by All”, Aug 2009.

[3] Wikipedia, the free encyclopedia, “Article on Visible Spectrum”, Nov 2012.

[4] Twibright Labs, “ronja.twibright.com”, 1998-2010

*5+ Dominic O’Brien, University of Oxford, “Visible Light Communications and other developments in Optical Wireless”, Communications groups at Oxford.

[6] Chung Ghiu Lee, Chosun University, South Korea, “Visible Light Communication”.

*7+ George Webster, CNN “ ’Li-Fi’ provides a light bulb moment for wireless web”, Sep 2012.

*8+ Mike Shaw, “Japanese firm to transmit data using visible light”, July 2012.

[9] Tom Matsumura, Secretary General, VLCC, Nakagawa Laboratories, “Visible Light Communications Activities”.

[10] Samsung Electronics, VLCC, University of Oxford, “Visible Light Communication”, Mar 2008.

*11+ “Li-Fi Development Kit *LDK+” by pureVLC, web site: www.purevlc.com.

[12] Li-Fi Consortium, “Welcome to Li-Fi Consortium”, Dec 2012.

[13] Visible Light Communication Consortium, “Prospectus”, Feb 2007 http://www.vlcc.net/modules/xpage3/.

[14] Durgesh Gujjari, Dalhousie University, “Visible Light Communication”, Aug 2012.

[15] Shinya Iwasaki, Eindhoven University of Technology, “Visible Light

28

road-to-vehicle communication using high-speed camera”, 2008

[16] Mohammad Shaifur Rehman, Md.

Mejbaul Haque, Ki-Doo Kim “Indoor

Positioning by LED Visible Light

Communication and Image Sensors”,

Dec 2011.