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1. A study of Visible light communication with Li-
Fi Technology
Amitoj Singh
Deparartment of Electronics & Technogloy
Guru Nanak Dev University,Amritsar.
amitojsunny@gmail.com
Abstract
The rate of increase in use mobile communication is very high. The established RF cellular
system is fully used and bandwidth reuse has been started to deal with increasing user demand.
But, this reuse is decreasing the network throughput and gap between user demands and network
capability is increasing continuously. The Visible Light Communication (VLC) is the best
solution for this scenario. It uses visible light region of electromagnetic spectrum, which is
10000 times broader than RF region. Implementation of VLC is similar to RF communication
system. Like Wi-Fi VLC has Light Fidelity (Li-Fi) which uses light as carrier. The problems
faced in RF system like bandwidth, availability, health, security can be overcome with VLC. The
VLC works by modulating the intensity of light from LED array which is detected by photo
detector (PD) and then demodulated to electronic signal. This paper gives an extensive overview
of working, applications and challenges for VLC and Li-Fi.
I. INTRODUCTION
The idea of using light as a communication medium was implemented by Alexander Graham
Bell in 1880 with his invention of the photo phone, a device that transmitted a voice signal on a
beam of light. Bell focused sunlight with a mirror and then talked into a mechanism that vibrated
the mirror. The vibrating beam was picked up by the detector at the receiving end and decoded
back into the voice signal, the same procedure as the phone did with electrical signals. But Bell
could not generate a useful carrier frequency, nor was he able to transmit the light beam from
point to point. Obstacles in nature such as fog and rain which could interfere with the photo
phone made Bell stop any future research into his invention. With the invention of LED (Light
Emitting Diode), the idea of using light as a communication medium has started again. VLC uses
white Light Emitting Diodes (LED), which send data by flashing light at speeds undetectable to
the human eye. One major advantage of VLC is that we can use the infrastructure around us
without having to make any changes to it. LEDs‟ ability to transfer information signals over light
(light which is between 400THz to 800THz of frequency and whose wavelength is between

2. 400nm to700nm) makes it a very good communication medium. Now the light we use in our
daily life can not only be used for providing light but also for communication.
Visible Light Communication Environment
VLC is much simpler than complex RF communication like IR, which is limited in power
because of its hazardous effects. Li-fi technology uses VLC. It is similar to Wi-Fi technology
with RF communication. The term Li-fi was first coined by Harald Haas, a German physicist. Li-
fi operates in the range of terahertz and it is free from the spectrum license.
Following are the important characteristics of VLC: -
1. Spectrum availability- VLC uses visible light region of electromagnetic spectrum, which is
10,000 time border than established communication. The frequency band for visible light is 430-
790 THz and for RF it is 3-300 GHz . Hence VLC is the best solution to fill the gap between
user demand and network capacity.

3. 2.Safety -VLC uses light as a carrier. Light is the source of life. Hence, there has no health
hazard. While in case of RF, it is proved to be hazardous for all living things.
3. Efficiency-VLC provides efficient way of communication due LED which require negligible
power and less complexity. It is inexpensive because of the use of already available visible light
sources. In case of RF communication, complexity and cost is very high.
4. Security-VLC is secure because of two main reasons : VLC signal is defined closely to
lightning area i.e. Line of sight communication and other is signals cannot be transmitted
through solid things like walls.
5. Unlicensed use-As VLC uses visible spectrum which is free. Hence, there are no licensing
issues.
6. High data rates-VLC inherits high data rates from optical communication.
Li Fi as coined by Prof. Harald Haas during his TED Global talk is bidirectional, high speed
and fully networked wireless communications, like Wi-Fi, using visible light. Li-Fi is a subset of
visible light communications (VLC) and can be a complement to RF communication (Wi-Fi or
Cellular network), or a replacement in contexts of data broadcasting.
It is wireless and uses visible light communication (instead of radio frequency waves), that is
part of the Optical Wireless Communications technologies, which carries much more
information, and has been proposed as a solution to the RF-bandwidth limitations. A complete
solution includes an industry led standardization process.
Working of LiFi-

4. o The input data usually in binary is fed to Lamp driver.
o Lamp Driver will directly modulate and drive the LED Lamp source.
o LED Lamp will flicker between ON & OFF at a speed which is not perceived by human
eye according to the input data.
o Photo detector will detect modulated light signal and convert it into electrical signal.
o This signal is further amplified and processed for intended applications
o During processing, the signal will again be converted into binary levels for use.
The data gathered from internet source is encoded by lamp driver which is connected to
LEDs or array of LEDs.The data can be transferred in two ways either by varying light
Intensity according to data pattern or by colors of illumination. Using the mixture of
different colors of LEDs with each frequency encoding a different data channel, the
system can operate up to 10Gbps speed. The light is modulated in such a way that
flickered light will not annoy the intended users.
The infrastructure needed to implement this technology is already established. Nowadays,
we have LED‟s everywhere in the form of lamps. The research to develop 1μm2 LED has
been started. Compare to today‟s 1mm2 LED‟s, the new LED‟s are able to flicker 1000
times faster and will transmits data millions times faster than normal LED‟s . Because of
small size, large group of LED‟s on a single source is possible. The First commercial
product of Li-Fi is been launched by OLEDCOMM. Fig. shows the example of LED
lamp used for Li-Fi implementation.
What’s New in 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 [12] 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 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

5. the connection is made in case of any light presence. There cannot be anything better than this
technology.
APPLICATIONS OF VLC AND LI-FI
Potential applications are as follows,
1. Aviation
Any RF operated gadget is not allowed in passenger airfcraft. Here LED‟s can perform dual
function of illumination and communication.
2. Vehicle transportation
Vehicles with tail and head LED lamp can act as a transmitter and receiver for VLC
communication. It will be easy to convey any message regarding traffic to vehicles. Efficient
intra-vehicle communication is possible. Traffic control becomes easier.

6. 3. Healthcare
In hospitals any RF application like Wi-Fi is banned because of its hazardous effects on human
health, it may affect the working of medical instruments. In this situation, Li-Fi which uses light
as medium will be best solution for communication in hospital campus.
5. Industrial
RF communication is dangerous in areas with burnable materials like mines, petrochemical,
power plants and petrol pumps. Here, Li-Fi can be used as safe alternative.
6. Underwater communication
Underwater RF communication is extremely difficult, but with VLC it is much easier.

7. 7. Commercial
VLC tags, ID‟s can be used in malls for localization and positioning purpose.
2. LITERATURE REVIEW
Nowadays, a lot of researchers are working on the development of light-emitting diode (LED)
lighting system. The LED lighting system can achieve lower power consumption and has a
longer life-time compared to the fluorescent lamp system. In this project, the characteristic of
short transient time in turning the light on/off processes was further investigated.
A high-speed wireless communication system, which is embedded in our LED lighting system,
was built. The duplex communication system consists of both downlink and uplink media
through different frequencies of lights. Several experiments were conducted in the visible light
-communication system. In this communication system, off-the self components were taken part
in building the driver circuit and the performance of the system was evaluated, such as, data
transmission rate, data transmission distance and the field of view of the transmitter.
[1] H. Elgala
In this paper, he gives differences between Radio and Visible Light Communication and declares
that Optical Wireless Communications has had a long history. Wide spread deployment of solid
state lighting (SSL) using LEDs is helping to drive this technology in the form of Visible Light
Communication (VLC). Data from an experimental systemsshows that data density‟s of 0.41
bits/second/Hz/m2 is being achieved from a VLC implementation.
[2]. W.O. Popoola, S. Rajbhandari, M. Amiri, S. Hashemi
In this paper, they have been proposed a number of modulation techniques and thoroughly
analyzed in literature. For optical wireless communication systems. Each modulation
Technique has its unique attractive features as well as its challenges. Some are very simple to
implement and bandwidth efficient like the On-Off keying (OOK). Pulse interval modulation
(PIM) techniques are reputed for their inherent synchronization pulse, subcarrier modulation
offers increased throughput, resilience to the inter-symbol interference (ISI) and immunity
against the fluorescent-light noise near DC, while pulse position modulation (PPM). Provides the
unparalleled power efficiency in line of sight (LOS) links but the performance degrades severely
in dispersed communication channel. There has been an enormous work on the analysis of these

8. and many more modulation techniques under different channel and environmental conditions; we
however present here a concise
Synopsis of the mostly reported wireless infrared modulation techniques.
[3]HU Guo-yong†1, CHEN Chang-ying1,2, CHEN
Zhen-qiang1 [4]:
In this paper, they conclude the possibility of visible red light laser being used as signal light
source for Free-Space Optical (FSO) communication is proposed. Based on analysis of
beams, performance of wireless laser communication link transmission in atmospheric channel
concerning 650 nm laser utilizing a low power red laser diode was evaluated. The proposed
system can achieve a maximum range of 300 m at data rate 100 Mb/s theoretically. An
experimental short-range link at data rate 10 Mb/s covering 300 m has been implemented in our
university. It is feasible to enhance the system performance such as link range and data rate by
increasing transmitting power and decreasing laser beam divergence angle or through other
approaches
. [4] Akassh, A. Mishra and Neelesh, S. Salient [5] :
In this paper, they give the idea of using internet using Visible Light Communication and also
said that wireless communication is the need of the hour. In the present fast paced life, there is a
strong urgency for the improvement in the means of communication. A Wireless network using
Visible Light Communication (VLC) is a newly emerging trend that can easily pave the way for
a comfortable wire-free future. Such a technology is useful to envision a smarter
personal wireless network, underwater communication and also in applications that provide
mobile services. This paper aims to explain the concept of VLC through its application to
provide Wireless Internet. It elaborates the use of Low Power Light Emitting Diodes (LEDs) for
transmission and reception along with the current and future prospects of this technology.
It also deals with the technical specifications for constructing such a network for real-time
purposes. In this experiment, we found that visible light was indeed an excellent medium to
transmit data. Since we used the low cost LED as our source, we barely had incurred much
VLC Modulation Techniques
There are a number of different methods that can be used to modulate the data over the visible
light spectrum, the main methods are
On-off keying (OOK): As the name suggests the data is conveyed by turning the LED off and
on. In its simplest form a digital „1‟ is represented by the light „on‟ state and a digital „0.
is represented by the light „off‟ state. The beauty of this method‟ is that it is really simple to
generate and decode. However, this method is not optimal in terms of illumination control and
data Throughput.
Pulse width modulation (PWM): This method conveys information encoded into the duration
of pulses. More than one bit of data can be conveyed within each pulse, but they may have to be
longer pulses than for OOK, so there is no great advantage with this scheme. It is also possible to
transmit data in an analogue format using this scheme which is also relatively simple to
implement.

9. .
Pulse position modulation (PPM): For PPM the data is encoded using the position of the pulse
within a frame. Again more than one bit can be transmitted in each pulse, however the duration
of the frame must be longer than for a single OOK bit so again it is not necessarily more
efficient. It does have the advantage of containing the same amount of optical energy within each
frame.
Variable Pulse Position Modulation (VPPM): This is similar to PPM but allows the pulse
width to be controlled for light dimming support. Pulse amplitude modulation (PAM), As
the name suggests, the information is carried by the amplitude of the pulse.
A number of data bits could be conveyed in a single pulse. e.g. off =00, 1/3 amplitude =01, 2/3
amplitude=10, full amplitude =11. In this example four different amplitude levels are used to
carry two bits of information. PAM can carry more data in each pulse than OOK, but it is
more complex and more susceptible to noise on the optical channel.
.
.
Colour shift keying (CSK): This can be used if the illumination system uses RGB type LEDs.
By combining the different colours of light, the output data can be carried by the colour itself and
so the intensity of the output can be constant The disadvantage of this system is the complexity
of both the transmitter and receiver.
.
Orthogonal Frequency Division Multiplex (OFDM): This modulation scheme has been widely
used for digital TV and radio and also for WiFi. It can be modified for use in optical
communications. OFDM uses a set of sub-carriers each at different but harmonically related
frequencies. There are a number of advantages including good spectral efficiency but
this method is quite complex to implement.
.
Spatial Modulation (SM): There are a number of techniques that allow one to determine the
source of an optical signal. If one can determine its source one can either use the multiple
sources of information to convey multiple stream of independent data (one from each source), or
one can use the source of the signal as part of the information encoding itself The multiple
sources could be multiple LEDs within a single fixture.
3. CHALLENGES FOR LIFI & VLC
VLC is still in the early stage that there are many severe problems or limitations needed to be
solved.
Line Of Sight (LOS): LOS is a definite advantage because the signal will be stronger. Visible
light signals can be reflected but does not penetrate most of objects in our daily life which cannot
penetrate most of objects in our daily life which can [6][7]. This characteristic can be also
considered as a disadvantage that preventing the signal from spreading among energies so that
the rate of communication without LOS between multiple rooms. And furthermore, reflection
can absorb much the transceivers is greatly limited [8]. Not any optical spread signal under

10. power regulation can be strong enough to let reflected signals still preserve enough power for
communication. If light levels are low and VLC receiver can
radio technology that indirect signals have a lower power and collect photons, it can receive data
at a lower data rate. Like hence the data rate reduces [6]
Duplex Transmission: VLC is a broadcast communication, and providing an upstream
communication channel is challenging. Several approaches have been considered, such as
using the infra-red (IR) or flashlight LED in the portable device for the upstream communication.
The use of radiofrequency (RF) to provide an upstream channel has also been considered
At present there is no concrete conclusion as to which solution is the best, and further work is
required to develop potential techniques and compare alternatives.
Transmitter Sources: Specialist LEDs with ideal characteristics for VLC would be great. Solid
state LED lighting is currently being sold based on its performance for illumination purposes
only. Communications performance is not even a secondary consideration so it is entirely
impractical to expect the lighting industry to aspect this into designs at this stage. In a practical
sense excellent results can be achieved with COTS LED devices. If better devices are available
for VLC then great otherwise to implement VLC existing LED devices can be considered [7]
Dimming Control: Another challenge in VLC is how to communicate when the lights are “off”.
If the lights are usually “on”, VLC transmission power comes free as it is already used for the
illumination. However during daytime, people tend to switch off the room lights. In order to
maintain the communication link, the LED should be “on”. In this case similar to RF wireless
communications, the power consumed for the data transmission is not free. One technique that
may be used is to reduce the LED brightness to a level low enough so that people will accept that
the light is “off” which solution is the best, and further work is required to develop potential
techniques and compare alternatives
Interference from sunlight: This problem is also associated with a wide transmission beams. In
visible light, this becomes more critical since the ambient light could be very strong that the
resulting SNR is low [7]. It is relatively simple to eliminate the vast majority of interference from
natural and artificial sources using optical filters [8]. After the photo-detector further analogue
and digital filtering ensure remaining interference is negligible
.
Equalization: The channel response can be equalised at the transmitter (pre-equalisation), at the
receiver (postequalisation typically suited to high bandwidth efficiency multilevel
modulation schemes. 100Mbit/s is possible using Discrete Multi-Tone Modulation (DMT). At
present there is little work in this area, and further studies are required in order to assess
the relative benefits of analogue equalization with relatively simple modulation, or complex
modulation and limited channel bandwidth.
Regulatory Challenges: In most cases VLC is subject to regulation by a non-communications
standard. This can be an eye-safety standard, illumination regulation, or an automotive
standard in the case of traffic signals or signal lights. A VLC standard must therefore encompass
both communications and associated illumination practices. This is distinct from most

11. associated illumination practices. This is distinct from most other communication standards, and
presents the challenge of coordination across regulatory bodies and frameworks Currently there
are activities in several areas. Within Japan VLCC has developed several national standards [6],
and the IEEE 802.15c Study Group on VLC is currently working on producing the necessary
documents to become a working group. Interest in these activities continues to grow, but perhaps
the major challenge for the VLC community is to develop links with other relevant regulatory
bodies to ensure compatibility of any techniques.
Li-Fi technology is based on LEDs for the transfer of data. The four major challenges/limitations
which the current wireless system faces are easily handled by this technology. Capacity, the first
challenge, as we know is very limited as compared to the visible light spectrum (ratio of
1:10000) and therefore no shortage of the ever increasing demand of wireless spectrum.
Availability, being the second issue is solved as light is easily accessible as compared to Wi-Fi.
For example in hospitals and airplanes radio waves cause interference and hence avoided.
Efficiency, is the issue of utmost concern as the radio cellular base stations consume a lot of
energy and mostly to cool them rather to transmit data and therefore only operational up to 5%
efficiency, on the other hand LEDs are highly efficient and energy consumption is never a
problem. Security, an issue which can‟t be neglected is a snap-if u can‟t see the light u can‟t
access the data while radio waves which can penetrate through walls make it prone to breach the
security protocols.
CONCLUSION
I have presented a study of visible light communication with Li-Fi technology. VLC gives the
advantage of a using an unregulated, unlicensed part of the electromagnetic spectrum
As it is a modern technology, VLC have many challenges but apart from it is ready for
implementation. It is greener, safer and brighter option for radio waves.
This technology has a bright scope in future. This technology demonstrated a solution to the
problem of integrating Visible Light Communication technology with present infrastructure
without having to make major changes to that infrastructure Visible Light Communication is a
rapidly growing segment of the field of communication. There are many advantages to using
VLC. There are also many challenges. VLC will be able to solve many of the problems
peoplehave been facing for many years, mainly environmental and power usage issues.
VLC is still in its beginning stages, but improvements are being made rapidly, and soon this
technology will be able to be used in our daily lives. In spite of the research problems it is our
belief that the VLC system will become one of the most promising technologies for the future
generation in optical wireless communication
ACKNOWLEDGEMENT

12. I am very thankful to department of Electronics and
Communication Engineering (ECE) of Guru Nanak Dev University (GNDU) Punjab India for
providing opportunity to write term paper on any topic of my interest. Special Thanks To
Coordinator Dr.ML SINGH for their valuable support in the completion of term paper.
REFERENCES
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[2] H. Elgala, "A Study on the Impact of Nonlinear
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