VISIBLE LIGHT COMMUNICATION

1. 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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2. 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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3. 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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4. Visible Light Communication
Siddharth Jhumat
Enrollment Number: 01016404812
M.Tech (Computer Science & Engineering)-REGULAR
University School of Information and Communication Technology
Abstract maintenance and environmental
friendliness. VLC is harmless for our
The Visible light communication health as well as our daily
(VLC) is a communication technology circumstances. In this term paper, I will
which uses visible light as optical carrier study how visible light can be used in
for data transmission and illumination. communication purpose, its advantages
Visible light is free. No company owns and disadvantages in day to day life and
property rights for visible light and thus how to overcome such disadvantages to
no royalty fees have to be paid nor does make it a success.
expensive patent-license have to be
purchased in order to use visible light Introduction
for communication purposes [1]. VLC Radio Waves extend from 3 kHz
offers a real alternatives to radio based to 300 GHz. They are used in mobile
communications since the spectrum is communication, radio communication,
free, plentiful, and the cost of communication satellites and other
implementation is actually less than navigation systems. The radio frequency
equivalent radio technology. Our spectrum is a limited natural resource.
wireless technology is based on radio Some of its limitations are:
waves which are limited, scarce and
expensive [2]. The visible light spectrum a. Different radio frequencies
is 10,000 times larger than the radio have different propagation
frequency spectrum. The prime function characteristics. Lower frequencies
of LEDs is to provide illumination. can propagate over large
Compared to traditional light sources, distances and higher frequencies
LEDs have the advantages of long life propagate over small distances.
expectancy, high lighting efficiency, easy
4

5. b. Radio frequency propagation RONJA (Reasonable Optical Near
does not obey political Joint Access)
boundaries of different countries.
Because of this nature of Ronja is an optoelectronic device
propagation, the RF spectrum has you can mount on your house and
to be shared among different connect your PC, home or office
nations. So the rules governing network with other networks [4]. Or you
the use of RF spectrum is can use it as a general purpose wireless
international in character. link for building any other networking
c. Different manufacturers produce project. The device has 1.4 km range
equipment in the frequency and has stable 10 Mbps full duplex data
bands most commonly used at rate. One Ronja device is a single long-
the global level. distance optical transceiver that is
capable of running against the same or
Visible spectrum has a frequency of 400- compatible device on the other side of
790 THz [3]. The visible spectrum is the the link. The topology is point-to-point.
portion of the electromagnetic spectrum The material costs are very low, about
visible to the human eye. Many species 100 USD. The operation is immune to
can see light with frequencies outside interference and quite reliable -
the visible spectrum for e.g. bees. 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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6. RONJA INSTALLATION OVERVIEW
RONJA ELECTRONICS OVERVIEW
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7. 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. LED (Light Emitting Diode)
In Visible light communication,
data is modulated on the light source By utilizing the advantage of fast
using modulation techniques like pulse switching characteristics of LED’s
position modulation or frequency shift compared with the conventional
keying. In the receiver end lightning, the LED illumination is used as
demodulation is performed using pulse a communication source. Since the
position modulation technique to fetch illumination exists everywhere, it is
the data back from the light source. So it expected that the LED illumination
is shown as a six step process – Sender device will act as a lighting device
Data, Modulation, Light Source, CMOS, and a communication transmitter
Demodulation, and Received Data. simultaneously everywhere in a near
future.
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8. LED’s are used in two propagation paths There are two types of visible
[5]: wavelength LED’s [6]:
1. Line of sight (LOS): Strong paths
are calculated using the 1. Single color LED – for example
illumination patterns of LED Red (R), Green (G) and Blue (B)
arrays. LED.
2. Diffuse: Modeled by assuming the 2. White LED – Uses phosphorous
room is equivalent to an for converting the emission
Integrating sphere. 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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9. phosphor and then the emitted light lens. LEDs emit light when energy levels
from the phosphor experiences change in the semiconductor diode. This
wavelength shift to a longer wavelength. shift in energy generates photons, some
As a result, the many wavelength of which are emitted as light. The
components are observed outside the specific wavelength of the light depends
LED. A white light can be generated on the difference in energy levels as well
from a blue LED with appropriate as the type of semiconductor material
phosphor. The emission spectrum of a used to form the LED chip. Solid-state
phosphor based LED has the strong design allows LEDs to withstand shock,
original blue spectrum and the longer vibration, frequent switching (electrical
wavelengths shifted by the phosphor. 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.
The basic LED consists of a Incandescent bulbs also waste 80
semiconductor diode chip mounted in percent to 90 percent of their energy on
the reflector cup of a lead frame that is heat generation to reach the
connected to electrical (wire bond) temperature for which (Kelvin scale)
wires, and then encased in a solid epoxy they are designed.
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10. Li-Fi Technology
transmitting more and more data are
Among the many new gadgets able to connect to the internet, either
unveiled at the recent Consumer through the mobile-phone network or
Electronics Show in Las Vegas was a pair
through Wi-Fi. But there is only a limited
of smart phones able to exchange data
using light. These phones, as yet only amount of radio spectrum available.
prototypes from Casio, a Japanese firm, Using light offers the possibility of
transmit digital signals by varying the breaking out of this conundrum by
intensity of the light given off from their exploiting a completely different part of
screens. The flickering is so slight that it the electromagnetic spectrum, one that
is imperceptible to the human eye, but is already present because it is used for
the camera on another phone can
another purpose: illumination.
detect it at a distance of up to ten
meters. In fact, they are the beginning of The rate of data transfer is also
a fast and cheap wireless-
good. Dr Povey's group is already up to
communication system.
130 megabits a second (faster than
some older Wi-Fi routers) over a
Light Signal 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 data being exchanged by The Li-Fi consortium reckons more than
Casio's phones were messages. But the 10 Gbps is possible. In theory, that
firm sees bigger applications, such as would allow a high-definition film to be
pointing a smart phone at an illuminated downloaded in 30 seconds.
shop sign to read information being
A big advantage of light is that it
transmitted by the light: opening times,
can be used in areas which contain
for example, or the latest bargains.
sensitive equipment that radio signals
As radio-based wireless is found might interfere with, such as aircraft and
everywhere, more and more devices operating theatres. LEDs in the ceiling of
10

11. an airliner would not only allow internet Association), the many mobile phones
access but could also transmit films on with infrared communication capability
demand to individual seats, removing will work as receivers. Today's devices
the need for lots of expensive and heavy almost always use RF-based solutions
cabling, thus saving airlines fuel. 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
There are limitations to using Gbit/s data rate. This can be used for
light, of course. Unlike radio, light waves docking solutions or to replace cable
will not penetrate walls. Yet for secure connections such as USB or Gigabit
applications that could be a bonus. And Ethernet.
light bulbs—some 14 billion of them
Dr. Harald Haas and his team at the UK's
around the world—are almost
University of Edinburgh, are the brains
everywhere and often on. As they are
behind this new patented technology
gradually replaced by LEDs, every home,
that uses beams of flickering light to
office, public building and even
transmit digital information wirelessly.
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
11

12. "My big idea is to turn light bulbs into way, then the signal will immediately cut
broadband communication devices ... so out," Thomas Kamalakis, a lecturer at
that they not only provide illumination, the Department of Informatics and
but an essential utility," he says. Haas Telematics at the Harokopio University
claims that data can be sent by adding a of Athens says.
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
Mark Leeson, associate professor
connection. In practice, it means that
at Warnick University’s School of
any street lamp could double up as a
Engineering also foresees challenges.
web hotspot. Less congestion means
“The question is how will my mobile
greater bandwidth and Haas says
phone communicate back with the light
transmission rates using "Li-Fi" could be
source?” Lennon asks.
as high as one gigabit a second --
meaning that downloads of high- Both are valid issues, Haas says,
definition films could take less time than but he has a simple workaround. "If the
sending a text. "We use what is already light signal is blocked, or when you need
there," he says. "The visible light to use your device to send information --
spectrum is unused, it's not regulated, you can seamlessly switch back over to
and we can communicate at very high radio waves."VLC is not in competition
speeds."[7] with Wi-Fi, he says, it is a complimentary
technology that should eventually help
Problems Associated:-
free up much needed space within the
"Of course one problem is that light radio wave spectrum."We still need Wi-
can't pass through objects, so if the Fi; we still need radio frequency cellular
receiver is inadvertently blocked in any systems. You can't have a light bulb that
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13. 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
The receiving device obtains the ID
close.
emitted by the LED device enabling it to
Transmit data using visible light download content relevant to the user
location.
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 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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14. also be used for stores in a shopping communication is prone to eaves
mall or buildings and in several dropping.
important events. In shopping malls
6. Unlicensed Spectrum: As VLC uses the
coupons and discounts can be
visible region of electromagnetic
transmitted using this technology.
spectrum, so it is free of cost.
Characteristics of VLC
VLC vs RF Communication
1. Human Safety: VLC poses no health
1. Limited Transmission Power: Unlike
hazard to human body [9]. Thus, the
VLC, in RF communications, the electric
transmission power can be kept high if
transmission power cannot be increased
needed.
beyond a prescribed level as it poses
2. High Data Rates: VLC inherits high serious health hazard for human body.
data rates from optical communications.
2. Regulated Spectrum: Due to radio
Thus it can be used for very high speed
wave restriction, there is no room to use
wireless communications.
more radio frequencies. In addition, the
3. Bandwidth: VLC exploits the visible use of radio spectrum is regulated.
region of electromagnetic spectrum.
3. Banned in Sensitive Areas: The radio
Thus it offers much larger frequency
wave cannot be used in hospitals and
band (300 THz) compared to that
space stations because it adversely
available in RF communications (300
affects the performance of precision
GHz).
instruments. These radio wave problems
4. Ubiquitous Nature: VLC uses the above are easily solved by use of the
already available visible light sources for visible light communications.
wireless communications, so it is
VLC vs IR Communication
expected to become a ubiquitous
technology in near future. Limited Data Rates: In IR communication
data rates cannot be increased beyond a
5. Security: As VLC involves line of sight
prescribed level as it poses serious
communication, so it is impossible to tap
threat to human eyes. This can be
the communication without breaking
attributed to the high energy density
the link. So it offers very secure
created by IrDA due to invisibility. The
communication and can be used in high
eye safety problem can be solved using
security military areas where RF
visible light communications. As
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15. compared to IR communication, the technologies owing to a small cost/
visible light communication is suitable to brightness and a large brightness/power
human eyes in terms of visibility. The ratio.
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.
Data Transmission
Modulation is the process of
varying one or more properties of a
high-frequency periodic waveform,
The VLC data rate is dependent called the carrier signal, with a
on the LED’s modulation bandwidth and modulating signal which typically
the standardization on physical layer contains information to be transmitted.
specifications has not yet been With respect to VLC, modulation
published. The transmission distance for schemes are used to transfer the data
VLC is possible up to several meters due given as a sequence of 0s and 1s into a
to its illumination requirement. Since series of light pulses. The two main
the infrared communication is used for a alternative modulation schemes are as
remote controller, the maximum follows [1] :-
distance is 3 meters.
The accompanying graph [10] 1. Sub-Carrier Pulse Position Modulation
depicts the true picture of the technical (SC-kPPM) – In Sub-Carrier Pulse
evolution of LEDs. It shows that in a few Position Modulation, the data is
years, LEDs will outshine all other separated into groups of log k bits each
15

16. 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.
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
2. Frequency Shift Keying (FSK) –
data-rate links, visible light
Frequency-shift keying (FSK) is a
communications advantages come to
frequency modulation scheme in which
the fore. Direct modulation eliminates
digital information is transmitted
the need for radio circuits, antenna
through discrete frequency changes of a
systems or complex receivers. Investing
carrier wave. Signal frequency
in ever more complex radio schemes at
determines whether or not the currently
increasingly higher frequencies is
transferred bit is 0 or 1. Two distinct
unnecessary when there is 10,000x
values (0 and 1) are represented by two
more visible light spectrum compared to
distinct pulse frequencies. This form of
radio spectrum. With data densities of
FSK is also referred to as binary FSK.
1000x those of radio the performance of
VLC looks very favorable.
16

17. Li-Fi Development Kit (LDK) decodes the received signal and encodes
the transmitter data onto the current
The Li-Fi Development Kit (LDK) supplied to the LED light fixture. The
[11] enables lighting manufacturers to unit is connected to the data network
add visible light Communications to via a standard Ethernet RJ45 port.
their products. There are two main
components:
1. VLC Ceiling Unit
2. VLC Desktop Unit
VLC Desktop Unit: The VLC Desktop Unit
contains the same VLC transceiver
module contained within the VLC Ceiling
LED Driver : Provided by the light fixture
Unit. It is equipped with an infra-red
or driver manufacturer, it usually
emitter and visible light detector. This
powers the LED light fixture directly. In
unit connects to client devices.
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
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18. Client Device: The client device is linked In an initial approach, the Li-Fi
to the VLC Desktop Unit using USB, e.g. Consortium defined different types of
Laptop Computer technology to provide secure, reliable
and ultra high-speed wireless
Li-Fi Consortium communication interfaces. Those are:
The Li-Fi consortium [12] is a non- 1. GigaSpeed technology
profit organization, devoted to
introduce optical wireless technology. 2. Optical mobility technology
The Li-Fi consortium’s charter members
are a leading group of international 3. Li-Fi environmental features
technology companies and research
institutions in optical communication GigaSpeed technology:-
technology. The group is based on a
The Li-Fi Consortium offers the
collectively developed concept and
fastest wireless data transfer technology
roadmap to establish a new wireless
available. Their current solutions cover
technology in the market, which exceeds
effective transmission rates of up to 10
the abilities and qualities of wireless RF
Gbit/s, allowing a 2 hour HDTV film to
technology.
be transferred within less than 30
The Li-Fi Consortium has several seconds. Smaller files are transferred
purposes: instantly.
1. Promote optical wireless a. GigaDock – It is a module that plugs
communications up to the multi-gigabit into mobile device. It provides up to
range in all their implementations. 10Gbit/s two way bus-like data transfer.
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.
18

19. b. GigaBeam – IR port in mobile device
for fast bulk transfers. 10 Gbit/s wireless
file transfers.
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
c. GigaShower – Ceiling unit used for
and the optical router. New optical
broadcasting large volumes of data. IR
receiver chips will be able to read
receivers are plugged into mobile
reflections, also of very weak signals. Its
devices to accept the data.
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
d. GigaMimo – It is a ceiling unit that phone as well as house phone. It
steers multiple beams. The beams can provides the fastest data transfer
be used to track user movement. method of a mobile device.
19

20. 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.
b. Optical Memo – It is an optical Li-Fi environment:-
memory stick having GigaSpeed
transceiver. It communicates with The concept of the Li-Fi cloud
mobile within a range of 2 m. 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
c. Optical Router – It is a hard drive for optical mode within a Li Fi cloud.
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.
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,
20

21. it lets you address intruders through interconnecting devices on and around
your TV or loudspeaker. 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
c. Smart Home Features – It can control Eun Tae Won. A great deal of emphasis
energy use through smart phone, it can is being placed on optimizing the
control electrical equipment through specification so that it works well within
smart phone, it can control heating and its particular constraints. For example,
air conditioning through smart phone 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
IEEE 802.15 WPAN TG7
using it to communicate the waviness of
visible light using a visible light element
VLC standardization efforts have
for the lighting, the signal, the lightning
been taking place since 2008 within the
notice, and the display, etc. as the
IEEE 802.15 working group, which is
above-mentioned, to standardize, and
charged with overseeing standards for
to spread it.
wireless personal area networks,
including body area networks (
21

22. Transmitter Circuit
The transmitter [14] side has a
voltage regulator, level shifter and the
LED driver circuit.
Voltage Regulator:-
The MAX3222 transceiver is a
The voltage regulator is for level shifter which takes the +/-12v
supplying constant voltage to the levels of RS-232 and converts them to 0
voltage shifter. It is needed because the to 5V of TTL levels. The RS-232 interface
unregulated voltage coming from our on the computer uses -3v to -12v logic 1
electricity provider can fluctuate greatly and +3 to +12v for logic 0. The
depending on several factors, including transmitter circuit, however, uses VCC
time of day and appliances powering on as a logic 1 and 0V as logic 0. MAX3222
and off. Using a voltage regulator is used to interface between the RS-232
compensates for all these problems and and TTL variants. It takes +/- 12V from
protects the MAX3222 level shifter. RS-232and gives out 0 to 5V.
MAX3222 Level Shifter:- LED Driver Circuit:-
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.
22

23. The signal from MAX3222 is sent Photodiode Driver Circuit:-
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 The capacitors C1, C2, C3 and C4 are the
photodiode driver circuit. The operation smoothing capacitors connected across
of the voltage regulator is same as in the DC supply to act as a decoupling
transmitter circuit. capacitor. Sometimes, the power supply
supplies an AC signal superimposed (also
MAX3222 Transceiver:- 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.
The operation of the MAX3222 is similar
to the operation explained in the So to summarize this we say that
transmitter circuit section in 4.7 with a the voltage regulator supplies constant
few changes. The output of the receiver voltage to the level shifter from the
circuit is fed to the pin 12 (T1IN) and the power supply by maintaining constant
pin 15 (T1OUT). DC voltages and avoiding unwanted
23

24. spikes in current. The level shifter helps Visible light road to vehicle
to convert the high voltages of RS-232 communication using high speed
(which are +/- 11V from the model camera [15]
computer) to transmitter and receiver
circuit levels (which are 0 to +5V). The Road to vehicle communication
electrical data from the computer is [15] is what helps drivers by providing
converted into optical data using LEDs traffic information. In Japan, VICS, shows
and transmitted over light, the optical traffic information on car navigation
data is captured by the receiver, display. Using camera as the receiver
converted into electrical data by the means that information is obtained from
photodiode and sent it to the client the intensity of the transmitter image
computer. 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.
24

25. 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.
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 Indoor Positioning by LED visible light
signal was modulated by using an ultra communication and image sensors [16]
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 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
25

26. each light has a different ID, which view some monitors for instance). This
shows a different exact location. This scenario is obviously incompatible with
positioning system can be used even in VLC and it might perhaps never be used
the underground subway station, in operating rooms.
shopping mall etc, where GPS is not Conditions such as fog and hazy
accurately used. The system is also very air also vastly hamper data transmission
convenient for the emergency use via visible light. Moreover, reflections
(Indoor Navigation System). This is used might occur on mirroring surfaces which
inside hospitals, too 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-
Difficulties world applications in the future. In some
fields of application it poses a favorable
Even though VLC can lead to alternative to conventional solutions
many interesting applications, as shown (infrared, WLAN etc.). The main goals for
in the previous sections, the technology the future are increasing the
is not entirely free of certain drawbacks transmission rate and improving
and difficulties. standardization. There are many
First of all, to successfully advantages to using VLC. There are also
transmit data, there has to exist a line of many challenges. VLC will be able to
sight between sender and receiver, solve many of the problems people have
because visible light cannot penetrate been facing for many years, mainly
solid items or objects. environmental and power usage issues.
A severe disadvantage of VLC in VLC is still in its beginning stages, but
the medical field is that it is sometimes improvements are being made rapidly,
imperative during surgery to switch off and soon this technology will be able to
background illumination (in order to be used in our daily lives.
26

27. Abbreviations *5+ Dominic O’Brien, University of
Oxford, “Visible Light Communications
VLC – Visible Light Communication and other developments in Optical
Wireless”, Communications groups at
LED – Light Emitting Diode
Oxford.
IEEE – Institute of electrical and
electronics engineers [6] Chung Ghiu Lee, Chosun University,
WLAN – Wireless Local Area Network South Korea, “Visible Light
GPS – Global Positioning System Communication”.
DC – Direct Current
*7+ George Webster, CNN “ ’Li-Fi’
AC – Alternating Current
provides a light bulb moment for
M.Tech – Master of Technology wireless web”, Sep 2012.
RF – Radio Frequency
Li-Fi – Light Fidelity *8+ Mike Shaw, “Japanese firm to
PPM – Pulse Position Modulation transmit data using visible light”, July
2012.
FSK – Frequency Shift Keying
VLCC – Visible light communication [9] Tom Matsumura, Secretary General,
consortium VLCC, Nakagawa Laboratories, “Visible
WPAN – wireless personal area network. Light Communications Activities”.
IR – Infra Red
[10] Samsung Electronics, VLCC,
OWC – optical wireless communication
University of Oxford, “Visible Light
LOC – Line of Sight
Communication”, Mar 2008.
Gbps – giga bits per second
*11+ “Li-Fi Development Kit *LDK+” by
References pureVLC, web site: www.purevlc.com.
[12] Li-Fi Consortium, “Welcome to Li-Fi
*1+ Christian Pohlmann, “Visible Light
Consortium”, Dec 2012.
Communication”, June 2010.
[13] Visible Light Communication
[2] P.K.Garg, “RF Spectrum – A Precious Consortium, “Prospectus”, Feb 2007
Natural Resource and its Efficient Use by http://www.vlcc.net/modules/xpage3/.
All”, Aug 2009.
[14] Durgesh Gujjari, Dalhousie
[3] Wikipedia, the free encyclopedia, University, “Visible Light
“Article on Visible Spectrum”, Nov 2012. Communication”, Aug 2012.
[4] Twibright Labs, [15] Shinya Iwasaki, Eindhoven
“ronja.twibright.com”, 1998-2010 University of Technology, “Visible Light
27

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.
28