LIGHT FIDELITY
SUBMITTED TO GOVERMENT POLYTECHNIC
ASTHAWAN
THIS IS CERTIFY THAT THE PROJECTREPORT ENTITILED LIFI TECHNOLOGY HAS BEEN COMPLETED SUCCESSFULLY
BY GROUP A
BRANCH:-MECHANICAL ENGINEERING SEMESTER :- VI
SESSION :-2019_2022
NAME OF GROUP MEMBER
1. SHASHI KUMAR (GROUP LEADER)
2.AAKASH KUMAR
3.ARCHANA KUMARI
TO GET THE PDF. FORMAT OF PROJECT GO TO BOTTOM OF THE POST
ABSTRACT
Whether you’re using wireless internet in a coffee shop,
stealing it from the guy next door, or competing for bandwidth at a conference,
you’ve probably gotten frustrated at the slow speeds you face when more than
one device is tapped into the network. As more and more people and their many
devices access wireless internet, clogged airwaves are going to make it
increasingly difficult to latch onto a reliable signal. But radio waves are
just one part of the spectrum that can carry our data. What if we could use
other waves to surf the internet? One German Physicist, 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, smart phones, 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.
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. The term Li-Fi was coined
by Prof. Haas when he amazed people by streaming high-definition video from a
standard LED lamp, at TED Global in July 2011. 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,” says Dr Povey,
Product Manager of the University of Edinburgh's Li-Fi Program ‘D-Light
Project’.
INTRODUCTION OF LI-FI TECHNOLOGY:-
LiFi (Light Fidelity) is a fast and cheap optical version of
Wi-Fi, the technology of which is based on Visible Light Communication (VLC).
LiFi 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. “At the heart of this technology is
a new generation of high brightness light-emitting diodes”, says Harald Haas
from the University of Edinburgh, UK, ”Very simply, if the LED is on, you
transmit a digital 1, if it’s off you transmit a 0,”Haas says, “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.
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.
In simple terms, Li-Fi can be thought of as a light-based
Wi-Fi. That is, 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.
Li Fi is now part of Visible Light Communication (VLC) PAN
IEEE 802.15.7 Standard. More sophisticated techniques could dramatically
increase VLC data rates. Team of scientists including Dr. Gorden Povey, Prof.
Harald Hass and Dr. Mostafa
Afgani
at University of Edinburgh and the University of Oxford are focusing on
parallel data transmission using arrays of LEDs, where each LED transmits a
different data stream. Other groups are using 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 stands for ‘Light Fidelity’.
Li-Fi is the terms have been used to label the fast and
cheap wireless communication system, which is the optical version of Wi –Fi.
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.
STANDARDIZATION
VLC communication is modeled after communication protocols
established by the IEEE 802 workgroup. This 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
count of the optical transmission mobility, its compatibility with artificial
lighting present in infrastructures, the defiance which may be caused by
interference generated by the ambient lighting. The MAC layer allows using the
link with the other layers like 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 kbit/s to 267.6 kbit/s.
•
The PHY II layer allows to reach data rates from 1.25 Mbit/s to 96
Mbit/s.
•
The PHY III is used for many emissions sources
with a particular modulation method called color shift keying (CSK). PHY III
can deliver rates from 12 Mbit/s to 96 Mbit/s.
The modulations formats recognized for PHY I and PHY II are
the coding on-off keying (OOK) and variable pulse position modulation (VPPM).
The Manchester coding used for the PHY I and PHY II layers include 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. This is an important point because the DC component allows to avoid
the light extinction in case of an extended line of logic 0.
The Li-Fi Consortium has also been established to work on
standardizing VLC communications, but the rapid evolution of the technology
minimizes the impact of any standardization effort. Both the IEEE 802 workgroup
and the Li-Fi Consortium
fail
to account for the emergence of optical orthogonal frequency division
multiplexing (O-OFDM) systems which provide significant benefits with regard to
data rates, multiple-access and energy efficiency.
VISIBLE LIGHT COMMUNICATIONS
“Visible light Communication (VLC) is a modern communication
technology which employs visible solid-state light sources (LEDs) for
transmitting data wirelessly as they are used for general illumination at the
same time."
VLC CHARACTERISTICS
The merits and demerits of this technology become apparent
once we go through the characteristics of visible light communication
technology:-
❖
Human Safety: VLC poses no
health hazards to human body. Thus, the transmission power can be kept high if needed.
❖
High Data
Rates: VLC inherits high data rates from optical communications. Thus, it
can be used for very high speed wireless communications.
❖
Bandwidth: Visible light
communications exploits the visible region of electromagnetic spectrum. Thus it
much larger frequency band ( 300 THz) compared to that available in RF
communications ( 300GHz).
❖
Ubiquitous
Nature: We have a well-established lighting infrastructure throughout the
world. In addition to it, LED based lighting devices are getting widespread
acceptance round the globe. Since VLC uses the already available visible light
sources for wireless communications, so it is expected to become a ubiquitous
technology in near future.
❖
Security: As VLC
involves line of sight communication, so it is impossible to tap the
communication without breaking the link. So it a very secure
communication
and can be used in high security military areas where RF communication is prone
to eavesdropping.
❖
Visibility: It is
aesthetically pleasing to see data being communicated by colored lights. Thus,
VLC is also used in many entertainment related activities like silent concerts,
decoration systems, etc.
❖
Unlicensed
Spectrum: As VLC uses the visible region of electromagnetic spectrum, so it
is free of cost. Contrary to it, the RF communication band is regulated
GENESIS
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
ISSUES
REGARDING RADIO-SPECTRUM
Radio
Spectrum is congested but the demand for wirelesses data double each year.
Everything, it seems want to use wireless data but the capacity is drying up.
⮚
Capacity:
In LI-FI the Bandwidth is 10000 times more than radio wave.
That provides huge range of spectrum bandwidth.
⮚
Efficiency:
Millions of base stations for radio wave transmission and
receiving on the earth consume huge amount of energy for transmitting the radio
waves and to cool the base station cabins. It gives only 5% Efficiency. In case
of LI-FI it does not consume energy as compare to other waves. It is very
cheap.
⮚
Availability:
Radio waves are available within the range of Base stations
which make it limited availability. It is unavailable in aircrafts because of
interference of wave cause crash. But LI-Fi does not produce interference and
provide user a perfect communication channel for accessing internet telephone,
watching movies online.
⮚
Security:
Radio
wave penetrates walls which cause security laps. Any one access to the private
network of any one and use their data, login to their secure region.
VLC VS RF COMMUNICATION
•
Limited
Transmission Power: In RF communications, the electric transmission
power cannot be increased beyond a prescribed level as it poses serious health
hazards for human body.
•
Regulated
Spectrum: Due to the radio wave restriction, there is no room to use more
radio frequencies. In addition, the use of radio spectrum is regulated.
•
Banned in
Sensitive Areas: The radio wave cannot be used in hospitals and Space
stations because it adversely acts the performance of precision instruments.
These radio wave problems above are easily solved by use of the visible light
communications.
All these problems can be solved using visible light
communications. This can be accredited to the high available bandwidth, high
data rates, high transmission power, health-friendly operation and lower
implementation costs of this technology.
WORKING OF LI-FI
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 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 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 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 it’s potential to compete with conventional Wi-Fi
has inspired the popular characterization Li-Fi.
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 this communication system are
1)
A high brightness white LED, Which acts as a
communication source and 2) A silicon photodiode which shows good response to
visible wavelength region serving as the receiving element?
LED can be switched on and off to generate digital strings of
1s and 0s. Data can be encoded in the light to generate a new data stream by
varying the flickering rate of the LED. To be clearer, by modulating the LED
light with the data signal, the LED illumination can be used as a communication
source. As the flickering rate is so fast, the LED output appears constant to
the human eye. A data rate of greater than 100 Mbps is possible by using high
speed LEDs with appropriate multiplexing techniques. VLC data rate can be
increased by parallel data transmission using LED arrays where each LED
transmits a different data stream. There are reasons to prefer LED as the light
source in VLC while a lot of other illumination devices like fluorescent lamp,
incandescent bulb etc. are available.
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; it's not regulated, and can
be used for communication at very high speeds.
TECHNOLOGY BRIEF:-
LI-FI CONSTRUCTION:-
The
LI-FI™ product consists of 4 primary sub-assemblies:
•
Bulb
•
RF power amplifier circuit
(PA)
•
Printed
circuit board (PCB)
•
Enclosure
The PCB controls the electrical inputs and outputs of the
lamp and houses the microcontroller used to manage different lamp functions.
An 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 sub
assemblies are contained in an aluminum enclosure.
Transmitters:
The following components are
used at the transmitting side:
1.
Colored LEDs
2.
Mosfets
3.
RS232 line driver IC
4.
USB to RS232 coverter cable
5.
Voltage Regulator
• Colored LEDs
An array of Red, Green and Blue LEDs are used at the
transmitter end as visible light sources. They are connected as loads in the
transistor circuitry. They are high power and emit a focused beam. Each color
is used to carry a different data stream.
• MOSFETs
A high speed N-type power MOSFET IRF 520 is used to modulate
the LEDs using OOK (On off Keying). The serial output from the computer is
converted into TTL Compatible form and is then applied to the gate of the
transistor. Thus, it switches the load (LEDs) on and off in accordance with the
input data 4.3.1.3 RS232 line driver
Since the output of computer is RS232 compatible, a 16 pin
RS232 line driver IC MAX 232 is used to make the computer output TTL level
compatible to drive the transistor circuit carrying through LED load..
•
USB to RS232 converter cable
In laptops, serial port is not available. Since data is to be
transmitted serially between the two computers, a USB to RS232 converter cable
is used to interface the serial output from MAX 232 IC to the laptop using the
built-in USB port. This cable contains an embedded controller to conform the
RS232 compatible data into USB protocol compatible form.
•
Voltage Regulator
A voltage regulator is used to supply constant voltage (5V)
to MAX232 IC.A 3 pin 7805 IC is used to serve the purpose.
Every kind of light source can theoretically be used as
transmitting device for VLC. However, some are better suited than others. For
instance, incandescent lights quickly break down when switched on and o_
frequently. These are thus not recommended as VLC transmitters. More promising
alternatives are fluorescent lights and LEDs. VLC transmitters are usually also
used for providing illumination of the rooms in which they are used. This makes
fluorescent lights a particularly popular choice, because they can flicker quickly
enough to transmit a meaningful amount of data and are already widely used for
illumination purposes. However, with an ever-rising market share of LEDs and
further technological improvements such as higher brightness and spectral
clarity. LEDs are expected to replace fluorescent lights as illumination
sources and VLC transmitters.
The
simplest form of LEDs is those which consist of a bluish to ultraviolet LED
surrounded
by phosphorus which is then stimulated by the actual LED and emits white light.
This leads to data rates up to 40 Mbit/s.
RGB LEDs do not rely on phosphorus any more to generate white
light. They come with three distinct LEDs (a red, a blue and a green one)
which, when lighting up at the same time, emit light that humans perceive as
white. Because there is no delay by stimulating phosphorus rust, Data rates of
up to 100 MBit/s can be achieved using RGB LEDs.
In recent years the development of resonant cavity LEDs
(RCLEDs) has advanced considerably. These are similar to RGB LEDs in that they
are comprised of three distinct LEDs, but in addition they are fitted with
Bragg mirrors which enhance the spectral clarity to such a degree that emitted
light can be modulated at very high frequencies. In early 2010, Siemens has
shown that data transmission at a rate of 500MBit/s is possible with this
approach.
It should be noted that VLC will probably not be used for massive data transmission. High data rates as the ones referred to above, were reached under meticulous Set ups which cannot be expected to be reproduced in real-life scenarios. One can expect to see data rates of about 5 kbit/s in average applications, such as location estimation. The distance in which VLC can be expected to be reasonably used ranges up to about 6 meters.
.
Receivers:
The
following components are used at the receiving side:
1.
Optical Receiver
2.
Optical Filters
3.
Voltage Regulator
4.
RS232 line driver IC
5.
USB to RS232 converter cable
Optical Receiver
A 6 pin fiber optic receiving module TORX 173 is used as the
light sensing device. On receiving light pulses, it gives a high output whereas
the output goes low in the absence of light.
•
Optical Filters
Red, green and blue light filters are used at the receiver to
de multiplex the multiple data streams. These are sharp narrowband filters. A
red light filter allows the frequency band corresponding to red color to pass
through it and blocks all other wavelengths. Thus, when a red light filters is
placed in front of the optical receiver, only the data stream carried by the
red beam falls at the receiver while the other streams are blocked. Similarly,
blue or green light filters can be used to allow the desired data stream to
reach the receiver.
•
Voltage Regulator
A voltage regulator is used to supply constant voltage (5V)
to TORX 173.A 3 pin 7805 IC is used to serve the purpose.
•
RS232 line driver
Since the output of TORX 173 is TTL level compatible, a 16
pin RS232 line driver IC MAX 232 is used to make the output RS232 compatible so
that the receiving module can be interfaced to the computer.
•
USB to RS232 converter cable
In laptops, serial port is not available. Since data is to be
transmitted serially between the two computers, a USB to RS232 converter cable
is used to interface the serial output from MAX 232 IC to the laptop using the
built-in USB port. This cable contains an embedded controller to conform the
RS232 compatible data into USB protocol compatible form
The most common choice of receivers are photodiodes which
turn light into electrical pulses. The signal retrieved in this way can then be
demodulated into actual data. In more complex VLC-based scenarios, such as
Image Sensor Communication even CMOS or CCD sensors are used (which are usually
built into digital cameras).
Modulation:
In order to actually send out data via LEDs, such as pictures
or audio files, it is necessary to modulate these into a carrier signal. In the
context of visible light communication, this carrier signal consists of light
pulses sent out in short intervals.
How these are exactly interpreted depends on the chosen
modulation scheme, two of which will be presented in this section. At first, a
scheme called subcarrier pulse position modulation is presented which is
already established as VLC-standard by the VLCC. The second modulation scheme
to be addressed is called frequency shift Keying, commonly referred to as FSK.
They also explore how to combine pulse- position modulation with illumination
control.
HOW IT’S DIFFERENT
LI-FI technology is base on LEDs for transfer of data. The transfer
of data can be with the help of all kinds of light can belong to the invisible,
ultraviolet or the visible part of the spectrum. The speed of internet is
incredibly high and we can download movies, games, music etc in just a few
minutes with the help of this technology. Also, this technology removes
limitation that has been put on the user by the Wi-Fi. We don’t need to in a
region that is WI-FI enabled to have access to the internet. We 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.
ECONOMIC VALUE
•
A free band that does not need license.
•
High installment cost but very low maintenance cost.
•
Cheaper than Wi-Fi.
•
Theoretical speed up to 1 GB per second : Less time & energy
consumption.
•
No more monthly broadband bills.
•
Lower electricity costs.
•
Longevity of LED bulb: saves money.
•
Light doesn't penetrate through walls: secured access.
LIMITATIONS
The main problem is that light can't pass through objects, so
if the receiver is inadvertently blocked in any way, then the signal will
immediately cut out. "If the light
signal is blocked, or when you need to use your device to send information
-- you can seamlessly switch back over to radio waves", Harald says.
Reliability and network coverage are the major issues to be
considered by the companies while providing VLC services. Interferences from external light sources like sun light, normal
bulbs; and opaque materials in the path of transmission will cause interruption
in the communication. High installation cost of the VLC systems can be
complemented by large-scale implementation of VLC though Adopting VLC
technology will reduce further operating costs like electricity charges,
maintenance charges etc.
APPLICATION AREA OF LI-FI TECHNOLOGY
It can be used in the places where it is difficult to lay the
optical fibres like hospitals. In operation theatre Li Fi can be used for
modern medical instruments.
Ø Airways:-
Whenever we travel through airways we face the problem in
communication media, because the whole airways communication are performed on
the basis of radio waves.
To overcome this drawback on
radio wave, li-fi is introduced.
Ø Green information technology:-
Green
information technology means that unlike radio waves and other communication
waves affects on the birds, human body etc.
Li-Fi never
gives such side effects on any living thing.
Ø
Free From Frequency Bandwidth
Problem:-
Li-fi is a communication media in the form of light, so no
matter about the frequency bandwidth problem. It does not require the any
bandwidth spectrum i.e. we don’t need to pay any amount for communication and
license.
Ø Increase Communication Safety:-
Due to visual
light communication, the node or any terminal attach to our network is visible
to the host of network.
Ø Multi User Communication:-
Li-Fi supports
the broadcasting of network; it helps to share multiple things at a single
instance called broadcasting.
⮚ Lightings Points Used as Hotspot in Smart
Homes and Offices:.
Any lightings device is performed as a hotspot it means
that the light device like car lights, ceiling lights, street lamps etc area
able to spread internet connectivity using visual light communication. This
helps us to low cost architecture for hotspot. Hotspot is a limited region in
which some amount of device can access the internet connectivity.
⮚ 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, interconnected 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. LiFi 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.
⮚
Undersea
Awesomeness:-
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 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 free 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.
It Could Keep You Informed and Save Lives
Say there’s an earthquake or a hurricane. Take your pick —
it’s a wacky city. The average people may not know what the protocols are for
those kinds of disasters. Until they pass under a street light, that is.
Remember, with Li-Fi, if there’s light, you’re online. Subway stations and
tunnels, common dead zones for most emergency communications, pose no
obstruction. Plus, in times less stressing cities could opt to provide cheap
high-speed Web access to every street corner. It can be used in petroleum or
chemical plants where other transmission or frequencies could be hazardous.
Traffic
Signals
In traffic signals Li Fi can be used which will communicate
with the LED lights of the cars and accident numbers can be decreased. Thousand
and millions of street lamps can be transferred to LiFi lamps to transfer data.
CHALLENGING
PROBLEMS
⮚
Connectivity while moving
⮚
Multiuser support
⮚
Dimming
⮚
Shadowing
SOLUTIONS TO CHALLENGING PROBLEMS
⦿ Solution for connectivity
This problem is similar to the connectivity problem in cellular network when you move from one area of the city to another area while speaking with cell-phone. The solution is called “handover”, using which the user is transferred from one BS to another Handover is done in the area that two BS’s have common coverage. Similar solution can be used in signal processing domain for VLC. The user can be transferred from one light source to another in the area that is under the coverage of both
⦿ Solution for multiuser
support
In this problem one solution is time division multiplexing (TDM). Each frame is divided into equal time slots. Each user transmits data in one time slot in a predefined order. The other solution is code division multiple access (CDMA). Codes are assigned to users. Each user transmits its data using the assigned signature pattern. It is used in 3G and 4G cellular networks. CDMA has been adopted and developed for optical systems. Optical orthogonal codes (OOC) are used as signature pattern for users.
⦿ Solution for shadowing
As shown before, the impulse response in VLC systems has two
parts. When the line-of-sight (LOS) part (which is received via direct path) is
blocked, the impulse response is only the second part. Then the data can be
recovered using the second part which is indeed the received data from the
indirect paths (multipath signal)
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.
REFERENCES:-
1. en.wikipedia.org/wiki/Li-Fi
2. teleinfobd.blogspot.in/2012/01/what-is-lifi.html
3. technopits.blogspot.comtechnology.cgap.org/2012/01/11/a-lifi-world/
5. the-gadgeteer.com/2011/08/29/li-fi-internet-at-thespeed-of-light/
6. www.macmillandictionary.com/buzzword/entries/Li-Fi.html
7. dvice.com/archives/2012/08/lifi-ten-ways-i.php
8.
Will Li-Fi be the new Wi-Fi?,
New Scientist, by Jamie Condliffe, dated 28 July 2011
9.
http://www.digplanet.com/wiki/Li-Fi
10. ”Visible-light
communication: Tripping the light
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