International Conference on Current Research in Engineering Science and Technology (ICCREST-2016)
ECO-FRIENDLY DATA TRANSMISSION
THROUGH LI-FI TECHNOLOGY
K. Stella1, R. Sivaranjani2, G. Nagasundari3.
1
PG student, Department of ECE, Vivekanandha College of Engineering for Women
PG student, Department of ECE, Vivekanandha College of Engineering for Women
3
PG student, Department of ECE, Vivekanandha College of Engineering for Women
2
Abstract: In recent era, most of the people are using
internet to achieve their task through wired or wireless
network. As number of users get inflate in wireless
network speed deflate proportionally. As per IEEE
802.11.n the Wi-Fi provides speed up to 150mbps,
although practically very less speed is received. To
overcome this limitation, we are introducing the concept
of Li-Fi. The Light Fidelity is a bidirectional, high speed
and fully networked wireless communication similar to
Wi-Fi. Li-Fi is a form of Visible Light Communication
(VLC). VLC uses rapid pulses of light to transmit
information that cannot be detected by the human eye.
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.
Keywords: Li-Fi, LED, Wi-Fi, visible light, data
transmission.
I
INTRODUCTION.
Over the past few years there has been a rapid
growth in the utilization of the RF region of the
electromagnetic spectrum. This is because of the huge
growth in the number of mobile phones subscriptions in
recent times. This has been causing a rapid reduction in
free spectrum for future devices. Light-fidelity (Li-Fi)
operates in the visible light spectrum of the electromagnetic
spectrum i.e. it uses visible light as a medium of
transmission rather than the traditional radio waves.
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 gigabitclass 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
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of these providing new capabilities to current and future
services, applications and end users. This brilliant idea
works very simple, if the LED is on, you transmit 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. [1].
Li-Fi can play a major role in relieving the heavy
loads which the current wireless systems face since it adds
a new and unutilized bandwidth of visible light to the
currently available radio waves for data transfer. Thus it
offers much larger frequency band (300 THz) compared to
that available in RF communications (300GHz). Also, more
data coming through the visible spectrum could help
alleviate concerns that the electromagnetic waves that come
with Wi-Fi could adversely affect our health. Li-Fi can be
the technology for the future where data for laptops, smart
phones, and tablets will be transmitted through the light in
a room. Security would not be an issue because if you can‘t
see the light, you can‘t access the data. As a result, it can be
used in high security military areas where RF
Communication is prone to eavesdropping.
II CONSTRUCTION OF LI-FI SYSTEM
Li-Fi is a fast and cheap optical version of Wi-Fi.
It 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.
The main components of Li-Fi system are as follows:
a) a high brightness white LED which acts as transmission
source.
b) a silicon photodiode with good response to visible light
as the receiving element.
LEDs can be switched on and off to generate
digital strings of different combination of 1s and 0s. To
generate a new data stream, data can be encoded in the light
by varying the flickering rate of the LED. The LEDs can be
used as a sender or source, by modulating the LED light
with the data signal. The LED output appears constant to
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the human eye by virtue of the fast flickering rate of the
LED. Communication rate greater than 100 Mbps is
possible by using high speed LEDs with the help of various
multiplexing techniques. VLC data rate can be increased by
parallel data transmission using an array of LEDs where
each LED transmits a different data stream. The Li-Fi
emitter system consists of 4 primary subassemblies[3]:
a) Bulb
b) RF power amplifier circuit (PA)
c) Printed circuit board (PCB)
d) Enclosure
The PCB controls the electrical inputs and
outputs of the lamp and houses the microcontroller used to
manage different lamp functions. A RF (radio-frequency)
signal is generated by the solid-state PA and is guided into
an electric field about the bulb. The high concentration of
energy in the electric field vaporizes the contents of the
bulb to a plasma state at the bulb‘s center; this controlled
plasma generates an intense source of light. All of these
subassemblies (shown in Fig. 1) are contained in an
aluminum enclosure [3].
Fig. 2. Bulb sub-assembly [10]
There are various inherent advantages of this
approach which includes high brightness, excellent color
quality and high luminous efficacy of the emitter – in the
range of 150 lumens per watt or greater. The structure is
mechanically robust without typical degradation and failure
mechanisms associated with tungsten electrodes and glass
to metal seals, resulting in useful lamp life of 30,000+
hours. In addition, the unique combination of high
temperature plasma and digitally controlled solid state
electronics results in an economically produced family of
lamps scalable in packages from 3,000 to over 100,000
lumens [4].
III WORKING OF LI-FI
Fig. 1. Block diagram of Li-Fi sub-assemblies
The bulb sub-assembly is the heart of the Li-Fi
emitter. It consists of a sealed bulb which is embedded in a
dielectric material. This design is more reliable than
conventional light sources that insert degradable electrodes
into the bulb [5]. The dielectric material serves two
purposes. It acts as a waveguide for the RF energy
transmitted by the PA. It also acts 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 high intensity and full
spectrum [3]. Figure 2 shows the bulb sub-assembly.
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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 10Gbps – meaning one can
download a full high-definition film in just 30 seconds.
[12].
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Fig:3 Implementation of Li-Fi
If the LED is on, you transmit 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
just 30 seconds. Simply awesome! But blazingly fast data
rates and depleting bandwidths worldwide are not the only
reasons that give this technology an upper hand. Since LiFi 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 LiFi. 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.
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Fig:4 Data transmission using LED
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 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.
IV TECHNICAL ASPECTS
LED as light source
The most important requirement for a light
source in order to serve communication purposes is the
ability to be switched on and off repeatedly in very short
intervals of time. Due to their ability to be switched on and
off rapidly, LEDs are suitable light sources for Li-Fi. LEDs
offer many benefits over fluorescent lamps and
incandescent lamps such as higher efficiency, environment
friendly manufacturing, flexibility of design, longer useful
lifetimes and improved spectrum performance.
LEDs emit light when the energy levels change in
the semiconductor diode. This change in energy generates
photons, some of which are emitted as light. The
wavelength of emitted light depends upon the difference in
energy levels and the type of semiconductor material used
to form the LED chip. Solid-state design allows LEDs to
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withstand vibration, shocks, frequent switching and
extremes of environment without compromising their long
useful lives of typically more than 100,000 hours.
identified. VPPM is similar to PPM but it allows the pulse
width to be controlled to support light dimming[11].
3. Colour Shift Keying (CSK): This is used if the
illumination system uses RGB-type LEDs. By combining
different colours of light, the output data can be carried by
the colour itself and hence the intensity of the output can be
near constant. Mixing of RGB primary sources produces
different colours which are coded as information bits[7].
The disadvantage is that it increases the complexity of the
transceivers.
4. Sub-Carrier Inverse PPM (SCIPPM): This method is
divided into two parts (1) sub-carrier part and (2) DC part.
The DC part is used only for lighting or indicating. When
there is no requirement for lighting or indicating, SCPPM
(Sub-Carrier PPM) is used in order to save energy.
5. Frequency Shift Keying (FSK): In this method, data
is represented by varying the frequencies of the carrier
signal. Before transmitting two distinct values (0 and 1),
there needs to be two distinct frequencies.
Fig 5:LED
The basic LED consists of a semiconductor diode
chip mounted in the reflector cup of a lead frame that is
connected to electrical (wire bond) wires, and then encased
in a solid epoxy lens. The variations in data rate with the
size of LEDs are very important in Li-Fi technology[10].
Different data rates can be achieved with different sized
LEDs. Normal sized LED bulbs can be reduced to microLEDs which handle millions of variations in light intensity.
A micro-LED light bulb can transmit 3.5 Gbps and data
rates of more than 10 Gbps are possible. The micro LED
bulbs allow the light stream to be beamed in parallel
thereby transmitting huge amounts of data in terms of
Gbps[6].
V MODULATION SCHEMES
1. On-Off Keying (OOK): The 802.15.7 standard uses
Manchester coding so that the period of positive pulses is
same as the period of negative ones, however this doubles
the bandwidth required for transmission. For higher bit
rates, run length limited (RLL) coding is used which is
spectrally more efficient. Dimming is supported by adding
an OOK extension which adjusts the aggregate output to
the correct level.
2. Variable Pulse Position Modulation (VPPM):
PPM encodes the data using the position of the pulse within
a set time period .The duration of the period containing the
pulse must be long enough to allow different positions to be
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6. SIM-OFDM (Sub-Carrier Index Modulation
OFDM): This is a new approach to transmission in which
an additional dimension is added to conventional 2D
amplitude/phase modulation (APM) techniques such as
quadrature amplitude modulation (QAM) and amplitude
shift keying.
Multiple Access
A seamless all-optical wireless network would
require ubiquitous coverage provided by the optical frontend elements. This necessitates the usage of a large amount
of Li-Fi enabled lighting units. The most likely candidates
for front-end devices in VLC are incoherent solid-state
lighting LEDs due to their low cost. Due to the physical
properties of these components, information can only be
encoded in the intensity of the emitted light, while the
actual phase and amplitude of the light wave cannot be
modulated. This significantly differentiates VLC from RF
communications[9]. A networking solution cannot be
realized without a suitable multiple access scheme that
allows multiple users to share the communication resources
without any mutual cross-talk.
Multiple access schemes used in RF
communications can be adapted for OWC as long as the
necessary modifications related to the IM/DD nature of the
modulation signals are performed. OFDM comes with a
natural extension for multiple accesses – OFDMA.
Single-carrier modulation schemes such as MPAM, OOK and PWM require an additional multiple
access technique such as frequency division multiple access
(FDMA), time division multiple access (TDMA) and/or
code division multiple access (CDMA)[8]. The results of
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an investigation regarding the performance of OFDMA
versus TDMA and CDMA are presented in Fig. 3.18
FDMA has not been considered due to its close similarity
to OFDMA, and the fact that OWC does not use super
heterodyning. In addition, due to the limited modulation
band width of the front-end elements, this scheme would
not present a very efficient use of the LED modulation
band width.
6. Data Density: Li-Fi can achieve about 1000 times the
data density of Wi-Fi because visible light can be well
contained in the tight illumination area.
7. Low Cost: As it requires very few components the cost
of it is comparatively low.
VII
LIMITATIONS OF LI-FI
1. As Li-Fi technology uses light as transmission medium,
so if the receiver is somehow blocked in a way then the
signal will immediately will be cut out.
2. While data transfer interference from external light
sources such as sunlight, normal bulbs, and opaque
materials can cause loss of reliability and network.
3. As Li-Fi works in direct line of slight. Slight disturbance
can cause to interruption.
VIII APPLICATION OF LI-FI
You Might Just Live Longer
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 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:6 Multiple Accesses
VI
ADVANTAGES OF LI-FI
Li-Fi technology is based upon lights might be
any sort of lights. The transfer of data takes place in
presence of any kinds of light whatever may be the band
width. Due to which the depend of transmitting the data or
information will be great and also sufficient information,
music, movies, games anything can be downloaded using
very less time.
1. Capacity: Light itself has 10000 times wider bandwidth
than radio waves. Due to which the transfer of data is more
effectively possible. So Li-Fi has better capacity.
2. Efficiency: LED lights consume less energy and very
efficient. As it uses less energy it is cheap and easy to use.
3. Availability: As light is present everywhere, Life is
available everywhere. But for more efficient use of Li-Fi
technology LED bulbs must be placed for proper
transmission on data for proper transmission on data.
4. Security: Light waves cannot penetrate through walls.
So they cannot be misused.
5. Bandwidth: The visible light is unlicensed and free to
use and gives a very large bandwidth.
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Smarter 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
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implemented solutions, but the draw on a power plant’s
own reserves could be lessened if they haven’t yet
converted to LED lighting.
for modern medical instruments. Moreover, no
electromagnetic interference is emitted by Li-Fi and thus it
does not interfere with any medical instruments such as
MRI scanners.
Underwater Explorations and Communications
Remotely operated underwater vehicles or ROVs
work well except in situations when the tether is not long
enough to fully explore an underwater area or when they
get stuck. If instead of the wires, light were used then the
ROVs would be freer to explore. With Li-Fi, the headlamps
could also then be used to communicate with each other,
data processing and reporting findings back to the surface
at regular intervals, while also receiving the next batch of
instructions. Radio waves cannot be used in water due to
strong signal absorption. Acoustic waves have low
bandwidth and disrupt marine life. Li-Fi offers a solution
for conducting short-range underwater communications.
Traffic
Airlines
Airline Wi-Fi. Nothing says captive audience like
having to pay for the "service" of dial-up speed Wi-Fi on
the plane. And don’t get me started on the pricing. The best
I’ve heard so far is that passengers will "soon" be offered a
"high-speed like" connection on some airlines. United is
planning on speeds as high as 9.8 Mbps per plane. I have
twice that capacity in my living room. And at the same
price as checking a bag, I expect it. Li-Fi could easily
introduce that sort of speed to each seat's reading light.
Medical and Healthcare
Due to concerns over radiation, operating rooms
do not allow Wi-Fi and even though Wi-Fi is in place in
several hospitals, interferences from computers and cell
phones can block signals from medical and monitoring
equipment. Li-Fi solves these problems. Lights are an
essential part of operating rooms and Li-Fi can thus be used
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Li-Fi can be used for communications between
the LED lights of cars to reduce and prevent traffic
accidents. LED headlights and tail-lights are being
implemented for different cars. Traffic signals, signs and
street lamps are all also transitioning to LED. With these
LED lights in place, Li-Fi can be used for effective vehicleto-vehicle as well as vehicle-to-signal communications.
This would of course lead to increased traffic management
and safety.
IX CONCLUSION
With the growing technology and increasing use
of the internet services, possibilities are very high that use
of Li-Fi technology will be soon in practice. Every bulb
will be replaced by Li-Fi bulbs and might be used like a
Wi-Fi hotspot for the transmission of data. Using Li-Fi
technology will grant a cleaner, greener and brighter future
and environment. The concept of Li-Fi is spreading so fast
as it is easy to use, it is attracting interest of people. The
use of Li-Fi technology gives a very golden opportunity to
replace or to give alternative to the radio based wireless
technologies. As the number of people and the access of
internet is increasing on such a large scale , accessing
internet through Wi-Fi will soon be insufficient as the
usage is increasing but the bandwidth remains the same. As
network traffic will increase it will result in lowering the
speed of accessing the internet thus more increasing prices.
The airways become clogged making it more difficult to
use. Thus the use of Li-Fi will increase the speed of data
transfer and also it is accessible in many banned places thus
it will be availsable for all.
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