Everything You Need to Know About Li-Fi Technology

LI-FI TECHNOLOGY
A Seminar Report submitted in partial fulfillment for the award of the
Degree of
BACHELOR OF TECHNOLOGY
By
SANJUSH S
(APAMEEE017)
Pursued in
Department of Electrical and Electronics Engineering
ARYANET INSTITUTE OF TECHNOLOGY
PALAKKAD
PALAKKAD
(Affiliated to Calicut University)
JANUARY 2016

PALAKKAD-678592, KERALA
DEPARTMENT OF ELECTRICAL & ELECTRONICS
ENGINEERING
CERTIFICATE
This is to certify that this is a bonafide record of the Seminar entitled “LI-FI
TECHNOLOGY” submitted by Sanjush.S to Aryanet Institute of Technology
Palakkad, in partial fulfilment for the award of the degree of BACHELOR OF
TECHNOLOGY in ELECTRICAL & ELECTRONICS ENGINEERING under
University of Calicut.
Guided by Staff in Charge Head of Department
Vyshakh A P Dr. B Sitalekshmi Amma Dr. B Sitalekshmi Amma
Asst Professor Professor & Head Professor & Head
Dept of EEE Dept of EEE Dept of EEE
SANJ
USH S
Digitally signed
by SANJUSH S
Date:
2017.01.17
11:47:25 +05'30'

Dept Of EEE LIFI TECHNOLOGY
AIT, Palakkad i
ACKNOWLEDGMENTS
I take this opportunity to thank my seminar guide, Vyshakh A P ,Asst Prof EEE for
his valuable guidance and encouragement which has been absolutely helpful in the successful
completion of this seminar.
I would also like to thank my Staff in charge Dr. B Sitalekshmi Amma, HOD EEE
for her valuable suggestions and support throughout.
I indebted to Dr. M R Vikraman, Principal AIT, Palakkad for his whole hearted
support for the completion of this seminar.
I also grateful to my Parents, Faculty members, Friends and all my well-wishers for
their timely aid without which I wouldn’t be able to finish my seminar successfully.
Last but not least; I would like to thank God Almighty for his blessings which made
me confident throughout the seminar.
SANJUSH S

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ABSTRACT
Li-Fi is a VLC, visible light communication, technology developed by a team of
scientists including Dr Gordon Povey, Prof. Harald Haas and Dr Mostafa Afgani at the
University of Edinburgh. Li-Fi is now part of the Visible Light Communications (VLC) PAN
IEEE 802.15.7 standard. “Li-Fi is typically implemented using white LED light bulbs. These
devices are normally used for illumination by applying a constant current through the LED.
However, by fast and subtle variations of the current, the optical output can be made to vary at
extremely high speeds. Unseen by the human eye, this variation is used to carry high-speed
data Dr. Harald Haas, has come up with a solution he calls “Data Through Illumination”—
taking the fiber out of fiber optics by sending data through an LED light bulb that varies in
intensity faster than the human eye can follow. It’s the same idea behind infrared remote
controls, but far more powerful. Haas says his invention, which he calls D-Light, can produce
data rates faster than 10 megabits per second, which is speedier than your average broadband
connection. He envisions a future where data for laptops, smartphones, and tablets is
transmitted through the light in a room. And security would be a snap—if you can’t see the
light, you can’t access the data.

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TABLE OF CONTENTS
DESCRIPTION PAGE NO
CERTIFICATE
ACKNOWLEDGMENT i
ABSTRACT ii
LIST OF FIGURES v
LIST OF TABLES vi
ABBEREVIATION / NOTATIONS / NOMENCLATURE vii
1. INTRODUCTION 1
1.1 Li-Fi: A New Paradigm in Wireless Communication 3
2. HISTORY OF LI-FI 5
3. WORKING OF LI-FI 6
3.1 Visible Light Communication 9
4. TECHNOLOGY BREIF 15
4.1 Working of Li-Fi: Light Source 15
4.2. Li-Fi Transmitter 16
4.3. Li-Fi Reeceiver 17
4.4. Modulation Technique for Li-Fi 18
4.4.1 Single Carrier Modulation 18
4.4.2 Multi Carrier Modulation 19
4.5 Li-Fi Standards 21
5. COMPARISON BETWEEN LI-FI AND WI-FI 23

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6. LI-FI NETWORK 26
6.1 Li-Fi Room Connector 26
6.2 Li-Fi Router 27
6.3 Li-Fi Cloud 28
6.3.1 Features of Li-Fi Cloud 29
7. APPLICATION AREA OF LI-FI TECHNOLOGY 30
7.1 Airlines 30
7.2 Medical Field 30
7.3 Lighting Point used as Hotspots 31
7.4 Power Plants 33
7.5 Marine Field 33
7.6 Smart Museums 34
7.7 Vehicles and Traffic Lights 35
8. ADVANTAGES AND LIMITATIONS 37
8.1 Advantages of Li-Fi 37
8.2 Limitations of Li-Fi 37
9. CONCLUSION 38
REFERENCES 39

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LIST OF FIGURES
FIGURE TITLE PAGE NO
1.1 Li-Fi Environment 3
1.2 Li-Fi technologies involving communication,
positioning, and many more 4
3.1 Working of Li-Fi 7
3.2 Li-Fi Sources 7
3.3 Giga Speed usage models 10
3.4 Frequency spectrum of EM waves 14
4.1 Block diagram of Li-Fi 17
6.1 Li-Fi Connector 27
6.2 Li-Fi Router 27
6.3 Li-Fi Cloud 28
7.1 Airlines 30
7.2 Marine Field 31
7.3 Street lamp as Li-Fi hotspots 32
7.4 Light emitting device as Li-Fi hotspots 32
7.5 Power plant 33
7.6 Undersea 34
7.7 Smart Museums 35
7.8 Vehicle Communication 36

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LIST OF TABLES
TABLE TITLE PAGE NO
5.1 Comparison between Li-Fi and Wi-Fi 23
5.2 Comparison between current and future
wireless technology 24

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ABBREVIATIONS/ NOMENCLATURE/ NOTATIONS
The abbreviations should be listed in alphabetical order as shown below.
ADC Analogue to Digital Converter
ACO-OFDM Asymmetrically Clipped Optical OFDM
BER Bit to Error Rate
CIM Colour Intensity Modulation
CSK Colour Shift Keying
GBPS Giga Bits Per Second
IDFT Inverse Discrete Fourier Transform
IR Infrared
ISI Inter Symbol Interference
LED Light emitting diode
Li-Fi Light Fidelity
LOS Line Of Sight Communication
MAC Media Access Control
MBPS Mega Bits Per Second
MIMO Multiple Input Multiple Output
OOK On-Oﬀ Keying
OSM Optical Spatial Modulation
OFDM Orthogonal Frequency Division Multiplexing
PHY Physical layer
PAM Pulse Amplitude Modulation
PPM Pulse Position Modulation

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PWM Pulse Width Modulation
QAM Quadrature Amplitude Modulation
SCM Single-Carrier Modulation
SNR Signal to Noise Ratio
U-OFDM Unipolar OFDM
VLC Visible Light Communication
Wi-Fi Wireless Fidelity
The meaning of special symbols and notations used in the report are shown below.
mA Milli Ampere
Ghz Giga hertz
Mhz Mega hertz
Thz Tera hertz
dB Decibel

Dept of EEE LI-FI TECHNOLOGY
AIT Palakkad 1
CHAPTER 1
INTRODUCTION
The technology underpinning Li-Fi was pioneered by German physicist Harald Haas,
currently based at the University of Edinburgh in the UK. Haas coined the term Li-Fi in 2011 in
the context of a talk presenting the new technology at the TED (Technology Entertainment and
Design) Global conference. The word quickly entered common parlance as an instantly
recoganisable alternative to Wi-Fi. Both terms are examples of abbreviations linguists sometimes
describe as clipped forms, i.e. Wi-Fi = wireless fidelity, Li-Fi = light fidelity.
Haas's research project, originally known as D-Light (short for Data Light), is now set to
launch a prototype Li-Fi application under the name of newly-formed company VLC (Visible
Light Communication) Ltd, which was set up to commercialize the technology.
In simple terms, Li-Fi can be thought of as a light-based Wi-Fi i.e, it uses light instead of
radio waves to transmit information. And instead of Wi-Fi modems, Li-Fi would use transceiver-
fitted LED lamps that can light a room as well as transmit and receive information. Since simple
light bulbs are used, there can technically be any number of access points.
This technology uses a part of the electromagnetic spectrum that is still not greatly
utilized- The Visible Spectrum. Light is in fact very much part of our lives for millions and
millions of years and does not have any major ill effect. Moreover there is 10,000 times more
space available in this spectrum and just counting on the bulbs in use, it also multiplies to 10,000
times more availability as an infrastructure, globally. It 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. More sophisticated techniques could dramatically increase VLC data rates. Teams at the
University of Oxford and the University of Edinburgh are focusing on parallel data transmission
using arrays of LEDs, where each LED transmits a different data stream. Other groups are using

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mixtures of red, green and blue LEDs to alter the light's frequency, with each frequency encoding
a different data channel.
Li-Fi, as it has been dubbed, has already achieved blisteringly high speeds in the lab.
Researchers at the Heinrich Hertz Institute in Berlin, Germany, have reached data rates of over
500 megabytes per second using a standard white-light LED. Haas has set up a spin-off firm to
sell a consumer VLC transmitter that is due for launch next year. It is capable of transmitting data
at 100 MB/s - faster than most UK broadband connections. Li-Fi is transmission of data through
illumination by taking the fiber out of fiber optics by sending data through a LED light bulb that
varies in intensity faster than the human eye can follow. Li-Fi is the term some have used to label
the fast and cheap wireless communication system, which is the optical version of Wi-Fi. The
term was first used in this context by Harald Haas in his TED Global talk on Visible Light
Communication. The heart of this technology is a new generation of high brightness light-
emitting diodes if the LED is on, they transmit a digital 1, if it‘s off it will transmit a 0. They can
be switched on and off very quickly, which gives nice opportunities for transmitted data.‖It 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 eye cannot notice, so the output
appears constant. More sophisticated techniques could dramatically increase VLC data rate.
Terms at the University of Oxford and the University of Edingburgh are focusing on parallel data
transmission using array of LEDs, where each LED transmits a different data stream. Other group
are using mixtures of red, green and blue LEDs to alter the light frequency encoding a different
data channel. Li-Fi, as it has been dubbed, has already achieved blisteringly high speed in the lab.
Researchers at the Heinrich Hertz Institute in Berlin, Germany, have reached data rates of over
500 megabytes per second using a standard white-light LED. The technology was demonstrated
at the 2012 Consumer Electronics Show in Las Vegas using a pair of Casio smart phones to
exchange data using light of varying intensity given off from their screens, detectable at a
distance of up to ten meters.

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Fig.1.1 Li-Fi Environment
In October 2011 a number of companies and industry groups formed the Li-Fi
Consortium, to promote high-speed optical wireless systems and to overcome the limited amount
of radio based wireless spectrum available by exploiting a completely different part of the
electromagnetic spectrum. The consortium believes it is possible to achieve more than 10 Gbps,
theoretically allowing a high-definition film to be downloaded in 30 seconds.
1.1 Li-Fi: A New Paradigm in Wireless Communication
Most of us are familiar with Wi-Fi (Wireless Fidelity), which uses 2.4-5GHz RF to
deliver wireless Internet access around our homes, schools, offices and in public places. We have
become quite dependent upon this nearly ubiquitous service. But like most technologies, it has its
limitations. While Wi-Fi can cover an entire house, its bandwidth is typically limited to 50-100
megabits per second (Mbps) today using the IEEE802.11n standard. This is a good match to the
speed of most current Internet services, but insufficient for moving large data files like HDTV
movies, music libraries and video games. The more we become dependent upon the cloud or our
own media servers to store all of our files, including movies, music, pictures and games, the more

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we will want bandwidth and speed. Therefore RF-based technologies such as today‘s Wi-Fi are
not the optimal way. In addition, Wi-Fi may not be the most efficient way to provide new desired
capabilities such as precision indoor positioning and gesture recognition. Optical wireless
technologies, sometimes called visible light communication (VLC), and more recently referred to
as Li-Fi (Light Fidelity), on the other hand, offer an entirely new paradigm in wireless
technologies in terms of communication speed, flexibility and usability.
Fig. 1.2: Li-Fi technologies involving communication, positioning, and many more

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CHAPTER 2
HISTORY OF LI-FI
Harald Haas, a professor at the University of Edinburgh who began his research in the
field in 2004, gave a debut demonstration of what he called a Li-Fi prototype at the TED Global
conference in Edinburgh on 12th July 2011. He used a table lamp with an LED bulb to transmit a
video of blooming flowers that was then projected onto a screen behind him. During the event he
periodically blocked the light from lamp to prove that the lamp was indeed the source of
incoming data. At TED Global, Haas demonstrated a data rate of transmission of around 10Mbps
comparable to a fairly good UK broadband connection. Two months later he achieved 123Mbps.
Back in 2011 German scientists succeeded in creating an 800Mbps (Megabits per second)
capable wireless network by using nothing more than normal red, blue, green and
white LED light bulbs thus the idea has been around for awhile and various other global teams
are also exploring the possibilities.

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CHAPTER 3
WORKING OF LI-FI
Li-Fi is typically implemented using white LED light bulbs at the downlink transmitter.
These devices are normally used for illumination only by applying a constant current. However,
by fast and subtle variations of the current, the optical output can be made to vary at extremely
high speeds. This very property of optical current is used in Li-Fi setup. The operational
procedure is very simple-, if the LED is on, you transmit a digital 1, if it‘s off you transmit a 0.
The LEDs can be switched on and off very quickly, which gives nice opportunities for
transmitting data. Hence all that is required is some LEDs and a controller that code data into
those LEDs. All one has to do is to vary the rate at which the LED‘s flicker depending upon the
data we want to encode. Further enhancements can be made in this method, like using an array of
LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the
light‘s frequency with each frequency encoding a different data channel. Such advancements
promise a theoretical speed of 10 Gbps – meaning one can download a full high-definition film in
just 30 seconds.
To further get a grasp of Li-Fi consider an IR remote fig 3.1. It sends a single data stream
of bits at the rate of 10,000-20,000 bps. Now replace the IR LED with a Light Box containing a
large LED array. This system, fig 3.2, is capable of sending thousands of such streams at very
fast rate.

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Fig 3.1 Working of Li-Fi
Light is inherently safe and can be used in places where radio frequency communication
is often deemed problematic, such as in aircraft cabins or hospitals. So visible light
communication not only has the potential to solve the problem of lack of spectrum space, but can
also enable novel application. The visible light spectrum is unused and it's not regulated, and can
be used for communication at very high speeds.
Fig 3.2 Li-Fi sources

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This brilliant idea was first showcased by Harald Haas from University of Edinburgh,
UK, in his TED Global talk on VLC. He explained, Very simple, if the LED is on, you transmit a
digital 1, if it‘s off you transmit a 0. The LEDs can be switched on and off very quickly, which
gives nice opportunities for transmitting data. So what you require at all are some LEDs and a
controller that code data into those LEDs. We have to just vary the rate at which the LED‘s
flicker depending upon the data we want to encode. Further enhancements can be made in this
method, like using an array of LEDs for parallel data transmission, or using mixtures of red,
green and blue LEDs to alter the light‘s frequency with each frequency encoding a different data
channel. Such advancements promise a theoretical speed of 10 Gbps –meaning you can download
a full high-definition film in just30 seconds. But blazingly fast data rates and depleting
bandwidths worldwide are not the only reasons that give this technology an upper hand. Since Li-
Fi uses just the light, it can be used safely in aircrafts and hospitals that are prone to interference
from radio waves. This can even work underwater where Wi-Fi fails completely, thereby
throwing open endless opportunities for military operations
Imagine only needing to hover under a street lamp to get public internet access, or
downloading a movie from the lamp on your desk. There's a new technology on the block which
could, quite literally as well as metaphorically, 'throw light on 'how to meet the ever-increasing
demand for high-speed wireless connectivity. Radio waves are replaced by light waves in a new
method of data transmission which is being called Li-Fi .Light-emitting diodes can be switched
on and off faster than the human eye can detect, causing the light source to appear to be on
continuously. A flickering light can be incredibly annoying, but has turned out to have its upside
,being precisely what makes it possible to use light for wireless data transmission. Light-emitting
diodes (commonly referred to as LEDs and found in traffic and street lights, car brake lights,
remote control units and countless other applications)can be switched on and off faster than the
human eye can detect, causing the light source to appear to be on continuously, even though it is
in fact 'flickering'. This invisible on-off activity enables a kind of data transmission using binary
codes: switching on an LED is a logical 1, switching it off is a logical '0'. Information can
therefore been coded in the light by varying the rate at which the LEDs flicker on and off to give
different strings of 1s and 0s. This method of using rapid pulses of light to transmit information

AIT Palakkad 9
wirelessly is technically referred to as Visible Light Communication (VLC), though it‘s potential
to compete with conventional Wi-Fi has inspired the popular characterization Li-Fi.
3.1 Visible light communication (VLC)
Many people‘s first exposure to optical wireless technology was VLC. This emerging
technology offers optical wireless communications by using visible light. Today, it is seen as an
alternative to different RF-based communication services in wireless personal-area networks. An
additional opportunity is arising by using current state-of-the-art LED lighting solutions for
illumination and communication at the same time and with the same module. This can be done
due to the ability to modulate LEDs at speeds far faster than the human eye can detect while still
providing artificial lighting. Thus while LEDs will be used for illumination, their secondary duty
could be to piggyback data communication onto lighting systems. This will be particularly
relevant in indoor smart lighting systems, where the light is always on. Other examples for
outdoor use include intelligent traffic systems to exchange data between vehicles, and between
vehicles and road infrastructure like traffic lights and control units. Alternatively, the LEDs‘
primary purpose could be to transmit information while the secondary purpose of illumination
would be to alert the user to where the data is being transmitted from. In contrast to infrared, the
so-called ―what you see is what you send‖ feature can be used to improve the usability of
transmitting data at shorter point-to-point distances between different portable or fixed devices.
There, illumination can be used for beam guiding, discovery or generating an alarm for
misalignment. The premise behind VLC is that because lighting is nearly everywhere,
communications can ride along for nearly free. Think of a TV remote in every LED light bulb
and you‘ll soon realise the possibilities of this technology.

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(A) Giga-Dock (B) Giga-Beam
(c) Giga-Shower (D) Giga-MIMO
Fig. 3.3: Giga Speed usage models (Images courtesy: Tri Lumina Corp.)
One of the biggest attractions of VLC is the energy saving of LED technology. Nineteen
per cent of the worldwide electricity is used for lighting. Thirty billion light bulbs are in use
worldwide. Assuming that all the light bulbs are exchanged with LEDs, one billion barrels of oil
could be saved every year, which again translates into energy production of 250 nuclear power
plants. Driven by the progress of LED technology, visible light communication is gaining
attention in research and development. The VLC Consortium (VLCC) in Japan was one of the
first to introduce this technology. After establishing a VLC interest group within the IEEE 802.15
wireless personal-area networks working group, the IEEE 802.15.7 task group was established by
the industry, research institutes and universities in 2008. The final standard was approved in

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2011. It specifies VLC comprising mobile-to-mobile (M2M), fixed-to-mobile (F2M) and
infrastructure-to-mobile (I2M) communications. There, the focus is on low-speed, medium-range
communications for intelligent traffic systems and on high-speed, short-range M2M and F2M
communications to exchange, for example, multimedia data. Data rates are supported from some
100 kbps up to 100 Mbps using different modulation schemes. Other standardisation groups are
working on standardised optical wireless communication solutions using visible and infrared
light.
Li-Fi comprises several optical wireless technologies such as optical wireless
communication, navigation and gesture recognition applied for natural user interfaces (Fig.3.3).
Thus it provides a completely new set of optical technologies and techniques to offer users add-
on as well as complementary functionalities compared to well-known and established RF
services. This could reach from a new user experience regarding communication speeds in the
gigabit-class to bridge the well-known spectrum crunch, over to precise indoor positioning or
controlling video games, machines or robots with entirely new natural user interfaces. Finally,
these and many more could be merged to a full-featured Li-Fi cloud providing wireless services
for other future applications as well. Li-Fi comprises a wide range of frequencies and
wavelengths, from the infrared through visible and down to the ultraviolet spectrum. It includes
sub-gigabit and gigabit-class communication speeds for short, medium and long ranges, and
unidirectional and bidirectional data transfer using line-of-sight or diffuse links, reflections and
much more. It is not limited to LED or laser technologies or to a particular receiving technique.
Li-Fi is a framework for all of these providing new capabilities to current and future services,
applications and end users. Usage models within a local Li-Fi cloud several data based services
are supported through a heterogeneous communication sys-tem. In an initial approach, the Li-Fi
Consortium defined different types of technologies to provide secure, reliable and ultra high-
speed wireless communication interfaces.
These technologies included giga-speed technologies, optical mobility technologies and
navigation, precision location and gesture recognition technologies. For giga-speed technologies,
the Li-Fi Consortium defined Giga-Dock, Giga-Beam, Giga-Shower, Giga-Spot and Giga-MIMO
models (Fig. 2) to address different user scenarios for wireless indoor and indoor-like data
transfers. While Giga-Dock is a wireless docking solution including wireless charging for smart
phones tablets or notebooks, with speeds up to 10 Gbps, the Giga-Beam model is a point-to-point

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data link for kiosk applications or portable-to-portable data exchanges. Thus a two-hour full
HDTV movie (5 GB) can be transferred from one device to another within four seconds. Giga-
Shower, Giga-Spot and Giga-MIMO are the other models for in-house communication. There a
transmitter or receiver is mounted into the ceiling connected to, for example, a media server. On
the other side are portable or fixed devices on a desk in an office, in an operating room, in a
production hall or at an airport. Giga-Shower provides unidirectional data services via several
channels to multiple users with gigabit-class communication speed over several meters. This is
like watching TV channels or listening to different radio stations where no uplink channel is
needed. In case Giga-Shower is used to sell books, music or movies, the connected media server
can be accessed via Wi-Fi to process payment via a mobile device. Giga-Spot and Giga-MIMO
are optical wireless single- and multi-channel hotspot solutions offering bidirectional gigabit-
class communication in a room, hall or shopping mall for example.
As the camera of your cellphone automatically receives these signals, it switches your
navigation software to use this information to guide you to the ATM machine you‘re looking for.
You conclude your ATM transaction and notice the Giga-Spot sign for instant digital movie
downloads. You pick out that new Tom Cruise movie using your phone‘s payment facility, and
then download within a few seconds the high-definition movie into the Giga-Link flash drive
plugged into the USB port of your smartphone. As you walk away, your phone notifies you that
the leather jacket Tom featured in the movie is on sale nearby. You walk over towards the show
window and your image comes up on the screen, wearing that coveted jacket. You turn and pose
while the image matches your orientation and body gestures for a ‗digital fitting.‘ When you walk
into the store, the clerk hands you the actual jacket in exactly your size. On the verge of a break
through first applications of Li-Fi have been put to use already, for example, in hospitals where
RF signals are a threat due to interference problems with medical equipment such as blood pumps
and other life supporting instruments. Axiomtek Europe presented such a product at the
Embedded World exhibition in Nürn-berg, Germany. The prototype of a mobile phone with an
incorporated VLC system was presented by Casio at the Consumer Electronics Show in Las
Vegas in January this year. In the coming years, we will see more Li-Fi products entering the
market, both in the industrial as well as consumer markets.

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Imagine only needing to hover under a street lamp to get public internet access, or
downloading a movie from the lamp on your desk. There's a new technology on the block which
could, quite literally as well as metaphorically, 'throw light on' how to meet the ever-increasing
demand for high-speed wireless connectivity. Radio waves are replaced by light waves in a new
method of data transmission which is being called Li-Fi. Light-emitting diodes can be switched
on and off faster than the human eye can detect, causing the light source to appear to be on
continuously
A flickering light can be incredibly annoying, but has turned out to have its upside, being
precisely what makes it possible to use light for wireless data transmission. Light-emitting diodes
(commonly referred to as LEDs and found in traffic and street lights, car brake lights, remote
control units and countless other applications) can be switched on and off faster than the human
eye can detect, causing the light source to appear to be on continuously, even though it is in fact
'flickering'. This invisible on-off activity enables a kind of data transmission using binary codes:
switching on an LED is a logical '1', switching it off is a logical '0'. Information can therefore be
encoded in the light by varying the rate at which the LEDs flicker on and off to give different
strings of 1s and 0s. This method of using rapid pulses of light to transmit information wirelessly
is technically referred to as Visible Light Communication (VLC), though its potential to compete
with conventional Wi-Fi has inspired the popular characterisation Li-Fi.
The concept of Li-Fi is currently attracting a great deal of interest, not least because it
may offer a genuine and very efficient alternative to radio-based wireless. As a growing number
of people and their many devices access wireless internet, the airwaves are becoming
increasingly clogged, making it more and more difficult to get a reliable, high-speed signal. The
opportunity to exploit a completely different part of the electromagnetic spectrum is therefore
very appealing. As well as being a potential solution to our ever-increasing hunger
for bandwidth, Li-Fi has other advantages over Wi-Fi, such as being safe to use on an aircraft, in
hospitals and medical devices, and even underwater, where Wi-Fi doesn't work at all.
Research suggests that Li-Fi has the potential to be faster, safer and cheaper than
conventional Wi-Fi technology. In more ways than one, it looks like the future of wireless
communication definitely has a 'bright side'.

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Li-Fi (Light Fidelity) is a fast and cheap optical version of Wi-Fi, the technology of which
is based on Visible Light Communication (VLC). VLC is a data communication medium, which
uses visible light between 400 THz (780 nm) and 800 THz (375 nm) as optical carrier for data
transmission and illumination. It uses fast pulses of light to transmit information wirelessly.
Fig 3.4: Frequency Spectrum of EM waves

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CHAPTER 4
TECHNOLOGY BRIEF
4.1 Working of LI-FI Light Sources
LI-FI is a new class of high intensity light source of solid state design bringing clean
lighting solutions to general and specialty lighting. With energy efficiency, long useful lifetime,
full spectrum and dimming, LI-FI lighting applications work better compared to conventional
approaches. This technology brief describes the general construction of LI-FI lighting systems
and the basic technology building blocks behind their function.
The LIFI product consists of 4 primary sub-assemblies:
• Bulb
• RF power amplifier circuit (PA)
• Printed circuit board (PCB)
• Enclosure
The heart of Li-Fi is the bulb sub-assembly which is the light source where a sealed bulb
is embedded in a dielectric material. This design is more reliable than conventional light sources
that insert degradable electrodes into the bulb. The dielectric material serves two purposes; first
as a waveguide for the energy transmitted by the power amplifier and second as an electric field
concentrator that focuses energy in the bulb. The energy from the electric field rapidly heats the
material in the bulb to a plasma state that emits light of very high intensity and full spectrum. The
design and construction of the Li-Fi light source enable efficiency, long stable life, and full
spectrum intensity that is digitally controlled and easy to use. The assembly will also consist of a
light receiver which is generally an LDR or any other light sensors. This sensor will receive the
transmitted data from the source. It will differentiate the subtle changes in the intensity of the
received light spectrum and it will be further decoded into electrical signal at the sub-assembly.
The control circuit board controls the electrical inputs and outputs of the lamp and houses the

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microcontroller used to manage different lamp functions. It decodes the receiver electrical signal
into varying light intensity which is coded as the 1s and 0s, and wise versa in the case of the light
receiver. All of these subassemblies are contained in an aluminium enclosure.
4.2 Li-Fi Transmitter
Conventional circuits that support OFDM or PAM involve a DAC to generate high-speed
signals. Typical DAC structures can only deliver upto 30mA current, and they require an
additional stage of current amplifier in order to drive a typical LED. An open-drain 8-bit current
steering DAC-based LED driver using CMOS technology has been developed and it omits the
additional current amplifier. The layout and package of the chip are shown. The ASIC is capable
of achieving 250 Mbps at a maximum full-scale current of 255mA and exhibits a power
efficiency of 72 percent. A differential optical drive is implemented by employing both current
steering branches of the DAC to drive two different colour LEDs. This doubles the signal level
and efficiency over a single ended approach, and enables the transmitter configuration described
in. The chip has four separate driver channels. Each channel is capable of driving up to two LEDs
allowing for CSK, lighting colour temperature adjustment and a Multiple Input Multiple Output
(MIMO) system. An increase in the full scale current results in a higher optical output power and
hence higher SNR at the receiver. The system is subject to non-linear distortions at the
transmitter and the receiver. Therefore, an SNR of about 25dB is required to achieve an uncoded
BER of 103. The BER does not improve when the current reaches about 250mA due to saturation
effects. It has been shown that it is possible to transmit 1Gbps when using all four drivers in
parallel in a MIMO configuration.

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Fig 4.1: Block diagram of Li-Fi
4.3 Li-Fi Receiver
Li-Fi systems are based on IM/DD. As a consequence, the average transmit power is
proportional to the transmit signal amplitude, and not the square of the signal amplitude. The
electrical path loss is hence twice the optical path loss. Therefore, in order to achieve reasonable
distances in an attocell network, receiver devices with sufficiently high sensitivity are required.
Based on computer modelling, it is indicated that an avalanche photo detector (APD)-based
receiver with a typical input referred noise density of 10 pA/Hz is necessary for reliable
communication. A Li-Fi receiver chip composed of 49 APD detectors (a 7 7 detector array) based
on 180 m CMOS technology has been developed. The size of each APD element is 200 m 200 m
placed on a 240 m grid. The responsivity of the nine APDs at the central core is 2.61 A/W at 450

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nm. An APD gain of 10 dB is achieved at a reverse bias voltage of only 10 V. Each APD is
connected to an integrated trans impedance amplifier (TIA) based on a shunt-shunt feedback
topology with xed gain in order to obtain good performance. The APDs achieve a bandwidth of
90MHz. The APDs outside the central core exhibit different colour sensitivities. Also, there are
several APDs at the fringe (numbers 6, 8 and 4248) that are exposed to a specially designed metal
grading structure to achieve enhanced directionality for angular diversity receiver algorithms.
4.4 Modulation techniques for Li-Fi
Li-Fi relies on electromagnetic radiation for information transmission. Therefore,
typically used modulation techniques in RF communication can also be applied to Li-Fi with
necessary modifications. Moreover, due to the use of visible light for wireless communication,
Li-Fi also provides a number of unique and specific modulation formats.
4.4.1 Single carrier modulation
Widely used Single-Carrier Modulation (SCM) schemes for Li-Fi include On Off Keying
(OOK), Pulse Position Modulation (PPM) and Pulse Amplitude Modulation (PAM). OOK is one
of the well known and simple modulation schemes, and it provides a good trade-off between
system performance and implementation complexity. By its very nature that OOK transmits data
by sequentially turning on and off the LED, it can inherently provide dimming support. As
specified in IEEE 802.15.7, OOK dimming can be achieved by rening the ON/OFF levels and by
applying symbol compensation. Dimming through rening the ON/OFF levels of the LED can
maintain the same data rate, however, the reliable communication range would decrease at low
dimming levels. On the other hand, dimming by symbol compensation can be achieved by
inserting additional ON/OFF pulses, whose duration is determined by the desired dimming level.
As the maximum data rate is achieved with a 50 dimming level assuming equal number of 1s and
0s, increasing or decreasing the brightness of the LED would cause the data rate to decrease.
Compared with OOK, PPM is more power-efficient but has a lower spectral efficiency. A variant
of PPM, termed Variable Pulse Position Modulation (VPPM), can provide dimming support by

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changing the width of signal pulses, according to a specified brightness level. Therefore, VPPM
can be viewed as a combination of PPM and Pulse Width Modulation (PWM). A novel SCM
scheme, termed Optical Spatial Modulation (OSM), which relies on the principle of spatial
modulation, proves to be both power- and bandwidth-efficient for indoor optical wireless
communication. As a vibrational scheme of Quadrature Amplitude Modulation (QAM) for single
carrier systems, Carrier-less Amplitude and Phase modulation (CAP) uses two orthogonal
signals, in place of the real and imaginary parts of the QAM signalling format, for spectrum-
efficient signal transmission in LiFi networks.
4.4.2 Multi-carrier modulation
As the required data rate increases in LiFi networks, SCM schemes such as OOK, PPM
and PAM start to suffer from unwanted effects, such as non-linear signal distortion at the LED
front-end and Inter-Symbol Interference (ISI) caused by the frequency selectivity in dispersive
optical wireless channels. Therefore, for high-speed optical wireless communication, efforts are
drawn to Multi Carrier Modulation (MCM). Compared with SCM, MCM is more bandwidth
efficient but less energy efficient. One and perhaps the most common realisation of MCM in Li-
Fi networks is Orthogonal Frequency Division Multiplexing (OFDM), where parallel data
streams are transmitted simultaneously through a collection of orthogonal sub carriers and
complex equaliser circuitry can be omitted. If the number of orthogonal subcarriers is chosen so
that the bandwidth of the modulated signal is smaller than the coherence bandwidth of the optical
channel, each sub channel can be considered as a at fading channel. Techniques already
developed for at fading channels can therefore be applied. The use of OFDM allows for further
adaptive bit and power loading techniques on each subcarrier so that enhanced system
performance can be achieved. An OFDM modulator can be implemented by an Inverse Discrete
Fourier Transform (IDFT) block, which can be efficiently realised using Inverse Fast Fourier
Transform (IFFT), followed by a Digital to Analogue Converter (DAC). As a result, the OFDM-
generated signal is complex and bipolar by nature. In order to t the IM/DD requirement imposed
by commercially available LEDs, necessary modifications to the conventional OFDM techniques
are required for LiFi.

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The commonly used method for ensuring a real-valued signal output after IFFT is by
enforcing Hermitian symmetry on the subcarriers. Moreover, as the light intensity cannot be
negative, the Li-Fi signal needs to be unipolar. There are many methods to obtain a unipolar
time-domain signal. DCO-OFDM uses a positive direct current (DC) bias for unipolar signal
generation. This method brings an increase in the total electrical power consumption, but without
further loss in spectral efficiency. Asymmetrically Clipped Optical OFDM (ACO-OFDM) is
another type of optical OFDM scheme where, as well as imposing Hermitian symmetry, only the
odd subcarriers are used for data transmission and the even subcarriers are set to zero. Therefore,
the spectral efficiency of ACO-OFDM is further halved. Since only a small DC bias is required in
ACO-OFDM, it is more energy efficient than DCOOFDM. Asymmetrically Clipped Direct
Current biased OFDM (ADO-OFDM) is a combination of DCO-OFDM and ACO-OFDM, where
the DCO-OFDM scheme is used on the even subcarriers and the ACO-OFDM scheme is used on
the odd subcarriers. In certain scenarios, it is shown that ADO-OFDM outperforms both DCO-
OFDM and ACO-OFDM in terms of power-efficiency. To incorporate dimming support into
optical OFDM, reverse polarity optical OFDM (RPO-OFDM) was proposed to combine the high
rate OFDM signal with the slow rate PWM signal both of which contribute to the overall
illumination of the LED. Since RPO-OFDM fully utilizes the linear dynamic range of the LED,
non-linear signal distortion is minimised. Another modulation scheme, termed Pulse-Amplitude-
Modulated Discrete Multi-tone Modulation (PAM-DMT), also clips the entire negative signal as
in ACO-OFDM. The diﬀerence is that PAM-DMT uses all of the available subcarriers for
information transmission, however, only the imaginary parts of the signal are modulated on each
subcarrier. In this way, signal distortion caused by asymmetric clipping falls on the real
component, and is orthogonal to the information-carrying signal. A hybrid optical OFDM scheme
combining ACO-OFDM and PAM-DMT, termed asymmetrically hybrid optical OFDM (AHO-
OFDM), uses both odd and even subcarriers for information transmission. In AHO-OFDM,
dimming capability is supported by a DC bias without a further requirement of the commonly
used PWM technique. The fact that compact multi-LED arrays can be realised straightforwardly
has led to a new OFDM technique that assigns subcarriers to physically separated LED sinan
array. This helps mitigation-linear distortions due to high peak-to-average power ratio (PAPR) in
OFDM.

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As an alternative to ACO-OFDM, ip-OFDM and Unipolar OFDM (U-OFDM) can
achieve comparable bit error ratio (BER) performance and spectral efficiency. A novel
modulation scheme, named enhanced unipolar OFDM (eU-OFDM), allows a unipolar signal
generation without additional spectral efficiency loss as in ACOOFDM, PAM-DMT, ip-OFDM
and U-OFDM. Recently, an alternative to OFDM has been proposed, which uses the Hadamard
matrix instead of the Fourier matrix as an orthogonal matrix to multiplex multiple data streams.
4.5 Li-Fi Standards
Like Wi-Fi, Li-Fi is wireless and uses similar 802.11 protocols; but it uses visible light
communication (instead of radio frequency waves), which has much-wider bandwidth. One part
of VLC is modelled after communication protocols established by the IEEE 802 workgroup.
However, the IEEE 802.15.7 standard is out-of-date. Specifically, the standard fails to consider
the latest technological developments in the field of optical wireless communications, specifically
with the introduction of Optical Orthogonal Frequency Division Multiplexing (OOFDM)
modulation methods which have been optimized for data rates, multiple-access and energy
efficiency. The introduction of O-OFDM means that a new drive for standardization of optical
wireless communications is required.
The IEEE 802.15.7 standard defines the physical layer (PHY) and media access control
(MAC) layer. The standard is able to deliver enough data rates to transmit audio, video and
multimedia services. It takes into account optical transmission mobility, its compatibility with
artificial lighting present in infrastructures, and the interference which may be generated by
ambient lighting. The MAC layer permits using the link with the other layers as with the TCP/IP
protocol.
The standard defines three PHY layers with different rates:
• The PHY I was established for outdoor application and works from 11.67 Kbps to 267.6 Kbps.

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• The PHY II layer permits reaching data rates from 1.25 Mbps to 96 Mbps. • The PHY III is
used for many emissions sources with a particular modulation method called Colour Shift Keying
(CSK). PHY III can deliver rates from 12 Mbps to 96 Mbps.
The modulation formats recognized for PHY I and PHY II are On-Oﬀ Keying (OOK) and
Variable Pulse Position Modulation (VPPM). The Manchester coding used for the PHY I and
PHY II layers includes the clock inside the transmitted data by representing a logic 0 with an
OOK symbol ‖01‖ and a logic 1 with an OOK symbol ‖10‖, all with a DC component. DC
component avoids light extinction in case of an extended run of logic 0‘s.

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CHAPTER 5
COMPARISION BETWEEN LI-FI & WI-FI
LI-FI is a term of one used to describe visible light communication technology applied to
high speed wireless communication. It acquired this name due to the similarity to WI-FI, only
using light instead of radio. WI-FI is great for general wireless coverage within buildings, and lifi
is ideal for high density wireless data coverage in confined area and for relieving radio
interference issues, so the two technologies can be considered complimentary. Comparison
between Li-Fi and Wi-Fi is shown in table 5.1.
Table 5.1: Comparison between Li-Fi and Wi-Fi

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Table 5.2: Comparison between current and future wireless technology
The table also contains the current wireless technologies that can be used for transferring
data between devices today, i.e .Wi-Fi, Bluetooth and IrDA. Only Wi-Fi currently offers very
high data rates. The IEEE 802.11.n in most implementations provides up to 150Mbit/s (in theory
the standard can go to600Mbit/s) although in practice you receive considerably less than this.
Note that one out of three of these is an optical technology.
Li-Fi technology is based on LEDs for the transfer of data .The transfer of the data can be
with the help of all kinds of light, no matter the part of the spectrum that they belong. That is, the
light can belong to the invisible, ultraviolet or the visible part of the spectrum. Also, the speed of
the internet is incredibly high and you can download movies, games, music etc in just a few
minutes with the help of this technology. Also, the technology removes limitations that have been

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put on the user by the Wi-Fi. You no more need to be in a region that is Wi-Fi enabled to have
access to the internet. You can simply stand under any form of light and surf the internet as the
connection is made in case of any light presence. There cannot be anything better than this
technology.

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CHAPTER 6
LI-FI NETWORK
A few additional features required to provide the same qualities as an RF-based wireless
network: A wireless local area network based on Li-Fi technology needs some additional features
to provide the same qualities as an RF-based wireless network, without losing the main
advantages Li-Fi technology is able to provide.
6.1 Li-Fi Room Connector
Optical signals, obviously they can‘t penetrate walls. How to the offence of many this is
an advantage (relation to security issues). However, in order to provide an optical wireless local
area network, rooms needs to be connected with each other. This is achieved via the Li-Fi room
connector.
The Li-Fi room connector is a replicator who sends the data stream from one side of the
wall to the other side of the wall via an optical fibre cable, which is connecting the two room
connectors on each side of the wall. With smaller rooms, the Li-Fi room connector might be
sufficient as the only Li-Fi hotspot in the room.

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Fig 6.1: Li-Fi connector
6.2 Li-Fi Router
The Li-Fi router is the networks connection to the external link (fibre optic cable, DSL,
GigE, etc.). The application is mainly useful for small office or home use with cloud & server
functions. It connects office and/or entertainment equipment and covers a radius of 20 meters
with a 100 Mbps transmission speed.
Fig 6.2: Li-Fi Router

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6.3 Li-Fi Cloud
The Li-Fi cloud is a software solutions enabling the user of controlling all the features
within a data centric Li--Fi environment. Part of this software has been developed already in
connection with the developments of the Li-Fi applications we offer per today. It‘s basically local
optical communication network with local data cloud structure and in house server/router. On the
move data transfer at 100 Mbit/s, including Giga Speed data transfer and reception upto 10
Gbit/s.
Fig 6.3: Li-Fi cloud

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6.3.1 Features of Li-Fi cloud
 Connects all office and entertainment equipment.
 Controls all data and entertainment equipment via smartphone.
 Displays all files on any screen (TV,PC, etc.).
 Supports file access from any point + and via any device.
 Stores all data in one central server/computer.
 Supports data transfer and reception at 10 Gbit/s.
 Supports "on the move" data transfer at 100 Mbit/s.
 Monitors the entire optical network area.
 Detects motion in the entire optical network area if wanted.
 Controls all security features via smart phone.
 Controls lighting via smart phone.
 Supports control of heating.
 Supports control of any connected electrical equipment.
 Supports energy saving/environmental features via smart phone.
 Bridges disparate data formats.
 Connects your local cloud to external line (fiberoptic, GigE, ADSL, etc.).

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CHAPTER 7
APPLICATION AREA OF LI-FI TECHNOLOGY
7.1 Airlines
Whenever we travel through airways we face the problem in communication medium
because the whole airways communication are performed on the basis of radio waves. To
overcomes this drawback on radio waves Li-Fi is introduce.
Fig 7.1: Airlines
7.2 Medical Field
For a long time, medical technology has lagged behind the rest of the wireless
world. Operating rooms do not allow Wi-Fi over radiation concerns, and there is also that whole

AIT Palakkad 31
lack of dedicated spectrum. While Wi-Fi is in place in many hospitals, interference from cell
phones and computers can block signals from monitoring equipment. Li-Fi solves both problems:
lights are not only allowed in operating rooms, but tend to be the most glaring (pun intended)
fixtures in the room.
Fig 7.2: Medical field
7.3 Lightings Points Used as Hotspot
Any lightings device is performed as a hotspot it means that the light device like
car lights, ceiling light street lamps etc area able to spread internet connectivity using visual light
communication. Which helps us to low cost architecture for hotspot. Hotspot is an limited region
in which some amount of device can access the internet connectivity.

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Fig 7.3: Shows every street lamps acting as a Li-Fi Hotspot.
Fig 7.4: Shows every light emmiting device acting as a Li-Fi Hotspot

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7.4 Power Plants
Wi-Fi and many other radiation types are bad for sensitive areas. Like those
surrounding power plants. But power plants need fast, inter-connected data systems to monitor
things like demand, grid integrity and (in nuclear plants) core temperature. The savings from
proper monitoring at a single power plant can add up to hundreds of thousands of dollars. Li-Fi
could offer safe, abundant connectivity for all areas of these sensitive locations. Not only would
this save money related to currently implemented solutions, but the draw on a power plant‘s own
reserves could be lessened if they haven‘t yet converted to LED lighting.
Fig 7.5: Power plants
7.5 In Marine Field
Underwater ROVs, those favourite toys of treasure seekers and James Cameron, operate
from large cables that supply their power and allow them to receive signals from their pilots
above. ROVs work great, except when the tether isn‘t long enough to explore an area, or when it

AIT Palakkad 34
gets stuck on something. If their wires were cut and replaced with light — say from a submerged,
high-powered lamp — then they would be much freer to explore. They could also use their
headlamps to communicate with each other, processing data autonomously and referring findings
periodically back to the surface, all the while obtaining their next batch of orders.
Fig 7.6: Undersea
7.6 Smart Museums
Li-Fi could enable a museum to deliver much more information on pieces in their
collection than those tiny cards they paste to the walls could ever dream of. It would be possible
to learn about the artist‘s history, listen to an audio tour, peruse recent auctions of their work.

AIT Palakkad 35
Fig 7.7: Smart Museums
7.7 In Vehicles and Traffic Lights
One of the smartest application of LIFI is sensors can be implanted in street lights,
possible sending your car info about road conditions, warning you about the guy you can‘t see
speeding towards the intersection, or instantly transmitting his plate number to the cops when he
does. Sensors implanted in front and rear bumpers could receive data transmitted from rear lights
of the car just veered into your lane while you were texting. Both drivers are warned (or may be
the car takes over) and the accident is averted.

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Fig 7.8: Vehicle Communication

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CHAPTER 8
ADVANTAGES AND LIMITATIONS
8.1Advantages of Li-Fi
 High speed, as high as 250 Gbps.
 Integrated into medical devices and in hospitals as this technology does not deal with radio
waves, so it can easily be used in such places where Bluetooth, infrared, Wi-Fi and internet
are banned. In this way, it will be most helpful transferring medium for us.
 High efficient Led light consumes less energy.
 Data through illumination and thus data transmission comes for free. We have the
infrastructure available and already installed. Efficiency Light box are already present.
 10000 times more spectrum than Radio waves.
 Security is another beneﬁt, It points out, since light does not penetrate through walls.
 Li-Fi may solve issues such as the shortage of radio frequency bandwidth
 By implementing the Technology worldwide every street lamp would be a free access point.
8.2 Limitations of Li-Fi
Apart from many advantages over Wi-Fi, Li-Fi technology is facing some challenges. Li-Fi
requires line of sight. When set up outdoors, the apparatus would need to deal with ever changing
conditions. Indoors, one would not be able to shift the receiving device. A major challenge facing Li-
Fi is how the receiving device will transmit back to transmitter. One more disadvantage is that visible
light can‘t penetrate through brick walls as radio waves and is easily blocked by somebody simply
walking in front of LED source . A side effect of Li-Fi is that your power cord immediately becomes
your data stream, so if you have power, you have internet.

AIT Palakkad 38
CHAPTER 9
CONCLUSION
The possibilities are numerous and can be explored further. If his technology can be put
into practical use, every bulb can be used something like a Wi-Fi hotspot to transmit wireless data
and we will proceed toward the cleaner, greener, safer and brighter future. The concept of Li-Fi is
currently attracting a great deal of interest, not least because it may offer a genuine and very
efficient alternative to radio-based wireless. As a growing number of people and their many
devices access wireless internet, the airwaves are becoming increasingly clogged, making it more
and more difficult to get a reliable, high-speed signal. This may solve issues such as the shortage
of radio-frequency bandwidth and also allow internet where traditional radio based wireless isn‘t
allowed such as aircraft or hospitals. One of the shortcomings however is that it only work in
direct line of sight.

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REFERENCES
1] S. Dimitrov and H. Haas. Principles of LED Light Communications–Towards Networked
LiFi. Cambridge University Press, Mar. 2015.
2] P.Chandhar and S. Das. Area Spectral Efﬁciency of Co-Channel Deployed OFDMA
Femtocell Networks. IEEE Trans. Wireless Commun., 13(7):3524–3538, July 2014.
3] V. Chandrasekhar, J. Andrews, and A. Gatherer. Femtocell Networks: A Survey. IEEE
Commun. Mag., 46(9):59–67, 2008.
4] W. C. Cheung, T. Quek, and M. Kountouris. Throughput Optimization, Spectrum
Allocation, and Access Control in Two-Tier Femtocell Networks. IEEE J. Sel. Areas
Commun., 30(3):561–574, Apr. 2012.
5] S. Dimitrov and H. Haas. Information Rate of OFDM Based Optical Wireless
Communication Systems With Nonlinear Distortion. J. Lightw. Technol., 31(6):918–929,
March 2013.
6] J. Andrews, F. Baccelli, and R. Ganti. A tractable approach to coverage and rate in
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7] V. Donald. Advanced mobile phone service: The cellular concept. The Bell System
Technical Journal, 58(1):15– 41, Jan 1979.
8] EuropeanStandardEN12464-1. LightingofIndoorWork Places, Jan. 2009.
9] H. Haas. Wireless Data from Every Light Bulb. TED Website, Aug. 2011.
10] H. Haas. High-speed Wireless Networking Using Visible Light. SPIE Newsroom, Apr.
19 2013.

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11] H S..Jo, P. Xia and J. Andrews. Downlink Femtocell Networks: Open or Closed? In
Proc. of IEEE Int. Commun. Conf. (ICC), pages 1–5, June 2011.
12] D. Stoyan, W. S. Kendall, and J. Mecke. Stochastic Geometry and its Applications. John
Wiley and Sons, 2nd edition, 1995.
13] D.Tsonev et al. A 3-Gb/s Single-LED OFDM-Based Wireless VLC Link Using a
Gallium Nitride µLED. IEEE Photon. Technol. Lett., 26(7):637–640, Apr. 2014.
14] F. Xiong. Digital Modulation Techniques. Artech House Publishers, 2nd edition edition,
2006.

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