li-fi seminar report
DESCRIPTION
Seminar report on Li-Fi TechnologyTRANSCRIPT
Acknowledgement
We would express our sincere regards to Prof. Oindri Ray, Department of Electronics and Communication
Engineering, Meghnad Saha Institute of Technology, for her proper guidance, valuable advice and constructive
suggestions for carrying out this seminar work.
We would like to record our indebtedness to Prof. Chandi Pani, TIC, Dept. of ECE and Dr. Utpal Ganguly,
Principal, Meghnad Saha Institute of Technology, for providing us all the facilities for carrying out this seminar.
We would also like to extend our sincere thanks to all faculty members of Electronics and Communication
Department.
Joshita Ghatak
Kaushik Chakrabarti
Chandradeep Chakravarti
Sarmishtha Basak
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INDEX
1. Introduction to Li-Fi Technology 1
2. History of Li-Fi 3
2.1 The need for Visible Light Communication (VLC) 3
2.2 Genesis of Li-Fi 3
3. Working principles 5
3.1 Visible light communication (VLC) 6
3.2 Technology in Brief 10
3.3 Working models 11
4. Comparison between Li-Fi & Wi-Fi 13
4.1 How is it different? 14
5. Application Areas of Li-Fi Technology 15
5.1 Airways 15
5.2 Medical applications 15
5.3 In traffic lights 15
5.4 Secure Communication 16
5.5 Multi User Communication 16
5.6 Lightings Points Used as Hotspot 16
5.7 Smarter Power Plants 17
5.8 Undersea Awesomeness 17
5.9 It could keep people informed and save lives 17
6. Advantage over Radio waves 18
7. Challenges For Li-Fi 19
8. Conclusion 20
9. References 21
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Chapter 1Introduction
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.
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 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.
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. Simply, if the LED is on, it transmits a digital 1, if it’s off it transmits 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
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University of Edinburgh are focusing on parallel data transmission using array 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
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.
The general term visible light communication (VLC), includes any use of the visible light portion of the
electromagnetic spectrum to transmit information. The D-Light project at Edinburgh's Institute for Digital
Communications was funded from January 2010 to January 2012. Haas promoted this technology in his
2011 TED Global talk and helped start a company to market it. PureLiFi, formerly pureVLC, is an original
equipment manufacturer (OEM) firm set up to commercialize Li-Fi products for integration with existing LED-
lighting systems.
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.
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Chapter 2History of Li-Fi
2.1 The need for Visible Light Communication (VLC)
Issues regarding Radio Waves:
1. Capacity:
Radio waves are limited, scar and expensive. We only have a certain range of it.
With the advent of the new generation technologies as of likes of 2.5G, 3G, 4G and so on we are
running out of spectrum.
2. Efficiency:
There are 1.4 million cellular radio base stations. They consume massive amount of energy.
Most of this energy is not used for transmission but for cooling down the base stations.
Efficiency of such a base station is only 5% and that raise a very big problem.
3. Availability:
We have to switch off our mobiles in aero planes.
It is not advisable to use mobiles at places like petrochemical plants and petrol pumps.
Availability of radio waves causes another concern.
4. Security:
Radio waves penetrate through walls.
They can be intercepted. If someone has knowledge and bad intentions then he may misuse it.
So we should look for other parts of EM waves.
Gamma rays are simply very dangerous and thus can’t be used for our purpose of communication. X-rays are
good in hospital and can’t be used either. Ultra-violet rays are sometimes good for our skin but for long duration it
is dangerous. Infra-red rays are bad for our eyes and are therefore used at low power levels. We have already seen
shortcomings of radio waves. So we are left with only Visible light spectrum.
2.2 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 coined the term Li-Fi and is widely recognized as the original founder of Li-Fi. He is Chairman of Mobile
Communications at the University of Edinburgh and co-founder of pureLiFi.
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Haas 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. In
2011 German scientists succeeded in creating an800Mbps (Megabits per second) capable wireless network by
using nothing more than normal red, blue, green and white LED light bulbs (here), thus the idea has been around
for awhile and various other global teams are also exploring the possibilities.
VLC technology was exhibited in 2012 using Li-Fi. By August 2013, data rates of over 1.6 Gbit/s were
demonstrated over a single color LED. In September 2013, a press release said that Li-Fi, or VLC systems in
general, do not require line-of-sight conditions.
One part of VLC is modeled after communication protocols established by the IEEE 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 (O-OFDM) modulation methods which have been optimized
for data rates, multiple-access and energy efficiency have. The introduction of O-OFDM means that a new drive
for standardization of optical wireless communications is required.
Nonetheless, 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 the optical transmission mobility, its compatibility with artificial lighting present in infrastructures, the
deviance which may be caused by interference generated by the ambient lighting. The MAC layer allows to use
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 modulation 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. The DC component avoids the light extinction in case of an extended line of logic
0.
VLC technology is ready to use right now; it's being installed in museums and businesses across France, and is
being embraced by EDF, one of the nation's largest utilities.
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Chapter 3Working principles
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. But unlike other light sources LEDs can turn
on & off millions of times per second. 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, it transmits a digital 1, if it’s off it transmits 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.
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Fig 3-1: Block Diagram of Li-Fi
To further get a grasp of Li-Fi consider an IR remote. 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 is capable of
sending thousands of such streams at very fast rate. 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 speed.
3.1Visible light communication (VLC): A potential solution to the global wireless spectrum shortage
LiFi (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. 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.
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.VLC can only be realized as an IM/DD system, which means that
the modulation signal has to be both real valued and unipolar. This limits the application of the well-researched
and developed modulation schemes from the field of RF communications. Techniques such as on-off keying
(OOK), pulse-position modulation (PPM), pulse-width modulation (PWM) and unipolar M-ary pulse-amplitude
modulation (M-PAM) can be applied in a relatively straightforward fashion. As the modulation speeds are
increased, however, these particular modulation schemes begin to suffer from the undesired effects of intersymbol
interference (ISI) due to the non-flat frequency response of the optical wireless communication channel. Hence, a
more resilient technique such as OFDM is required. OFDM allows adaptive bit and energy loading of different
frequency sub-bands according to the communication channel properties. This leads to optimal utilization of the
available resources. OFDM achieves the throughput capacity in a non-flat communication channel even in the
presence of nonlinear distortion. Such channel conditions are introduced by the transfer characteristic of an off-
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the-shelf LED that has a maximum 3 dB modulation bandwidth in the order of 20 MHz. In fact, the record-
breaking results have all been achieved using OFDM. Further benefits of this modulation scheme include simple
equalization with single-tap equalizers in the frequency domain as well as the ability to avoid low-frequency
distortion caused by flickering background radiation and the baseline wander effect in electrical circuits.
Conventional OFDM signals are complex-valued and bipolar in nature. Therefore, the standard RF OFDM
technique has to be modified in order to become suitable for IM/DD systems. A straightforward way to obtain a
real-valued OFDM signal is to impose a Hermitian symmetry constraint on the sub-carriers in the frequency
domain. However, the resulting time-domain signal is still bipolar. One way for obtaining a unipolar signal is to
introduce a positive direct current (DC) bias around which the amplitude of the OFDM signal can vary as shown
in Figure.
(a) Unbiased bipolar OFDM signal (b) Biased unipolar OFDM signal
Fig 3-2
The resulting unipolar modulation scheme is known as DC-biased optical OFDM (DCO-OFDM). The addition of
the constant biasing level leads to a significant increase in electrical energy consumption. This can be easily
visualized when Fig 3-2 (a) and Fig 3-2(b) are juxtaposed. However, if the light sources are used for illumination
at the same time, the light output as a result of the DC bias is not wasted as it is used to fulfill the illumination
function. Only if illumination is not required, such as in the uplink of a Li-Fi system, the DC bias can significantly
compromise energy efficiency. Therefore, researchers have devoted significant efforts to designing an OFDM-
based modulation scheme which is purely unipolar. Some well-known solutions include: asymmetrically clipped
optical OFDM (ACO-OFDM), pulse-amplitude-modulated discrete multi-tone modulation (PAM-DMT), unipolar
OFDM (U-OFDM), Flip-OFDM, spectrally-factorized optical OFDM (SFO-OFDM). The general disadvantage of
all these techniques is a 50% loss in spectral efficiency, i.e., the data rates are halved. This limitation has recently
been overcome by researchers at the University of Edinburgh.
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3.1.1 Multiple access using VLC
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 VLC 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 M-PAM, 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). The results of an investigation regarding the performance of OFDMA
versus TDMA and CDMA are presented in Fig 3-3. FDMA has not been considered due to its close similarity to
OFDMA, and the fact that OWC does not use superheterodyning. In addition, due to the limited modulation
bandwidth of the front-end elements, this scheme would not present a very efficient use of the LED modulation
bandwidth.
Fig 3-3: TDMA vs. OFDMA vs. CDMA (with optical orthogonal code) in a six-user scenario
As shown in Fig. 3-3, CDMA is very inefficient as the use of unipolar signals creates significant interchannel
interference (ICI) and a substantial increase in the power requirements compared to its application in RF
communications. At the same time, the performance of TDMA barely surpasses that of OFDMA for the different
scenarios. The higher power requirement of OFDMA compared to TDMA is caused by its wider time- domain
signal distribution. This leads to the need for higher DC biasing levels and as a consequence to higher power
consumption which is reflected in the shown signal-to-noise ratio (SNR). In a practical scenario where the
functions of communication and illumination are combined, the difference in power consumption between the
different schemes would diminish as the excess power due to the DC bias would be used for illumination
purposes. It should be pointed out that this investigation has been performed for a flat linear additive white
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Gaussian noise (AWGN) channel where only clipping effects from below, applicable only to OFDMA, have been
considered. This is due to the fact that nonlinear effects such as clipping from above as well as the nonlinear
relationship between the modulating current signal and the emitted optical signal are device-specific, while
clipping from below is inherent to any IM/DD system. Furthermore, low-frequency distortion effects from the
DC-wander in electrical components as well as from the flickering of background light sources are also not
considered. In a practical scenario, these effects would not be an issue for OFDMA, but are expected to decrease
the performance of TDMA and CDMA. Therefore, the design complexity of a TDMA or CDMA system increases
as suitable techniques to deal with these problems need to be implemented. It is also worth noting that the non-
flatness of the channel in a practical scenario would further degrade the performances of CDMA and TDMA
compared to OFDMA.
In VLC there exists an additional alternative dimension for achieving multiple access. This is color, and the
corresponding technique is wavelength division multiple access (WDMA). WDMA harnesses the different light
wavelengths to facilitate multiple-user access. This scheme could reduce the complexity in terms of signal
processing. However, it would lead to increased hardware complexity as well as to the need at each access point
for multiple transmitter elements with narrow wavelength emission. This immediately puts strict requirements on
the optical front-end elements, and compromises SNR and, hence, capacity. In addition, WDMA excludes the
usage of a large variety of off-the-shelf LEDs as most of them are not optimized for WDMA. The typical
emission profile of an off-the-shelf white LED is illustrated in Fig 3-4. At the same time, light sources with
different narrow wavelength emission spectra have different modulation frequency profiles as well as different
optical efficiencies. When combined with the varying responsivity of photo detectors at different wavelengths, as
shown in figure, these differences complicate immensely the fair distribution of communication resources
between multiple users.
(a) Typical spectrum of a white-phosphor LED (b) Typical responsivity of a photodetector.
Fig 3-4
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3.2 Technology in Brief
LI-FI is a new class of high intensity light source of solid state design bringing clean lighting solutions to general
and specialty lighting. It is a 5G visible light communication system that uses light from light-emitting
diodes (LEDs) as a medium to deliver networked, mobile, high-speed communication in a similar manner as Wi-
Fi. Visible light communications (VLC) works by switching bulbs on and off within nanoseconds, which is too
quickly to be noticed by the human eye. Although Li-Fi bulbs would have to be kept on to transmit data, the bulbs
could be dimmed to the point that they were not visible to humans and yet still functional. The light waves cannot
penetrate walls which makes a much shorter range, though more secure from hacking, relative to Wi-Fi. Direct
line of sight isn't necessary for Li-Fi to transmit signal and light reflected off of the walls can achieve 70 Mbit/s.
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.
3.2.1 Li-Fi Construction
The LIFI™ product consists of 4 primary sub-assemblies:
• Bulb
• RF power amplifier circuit (PA)
• Printed circuit board (PCB)
• Enclosure Fig 3-5: Li-Fi bulb with PCB
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 subassemblies are contained in an aluminum enclosure.
Function of the bulb:
The heart of LIFI™ is the bulb sub-assembly 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 RF energy transmitted by the PA and second,
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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.
3.2.2 Uplink
Up until now, research has primarily focused on maximizing the transmission speeds over a single unidirectional
link. However, for a complete Li-Fi communication system, full duplex communication is required, i.e., an uplink
connection from the mobile terminals to the optical AP has to be provided. Existing duplex techniques used in RF
such time division duplexing (TDD) and frequency division duplexing (FDD) could be considered, where the
downlink and the uplink are separated by different time slots, or different frequency bands respectively. However,
FDD is more difficult to realize due to the limited bandwidth of the front-end devices, and because
superheterodyning is not used in IM/DD systems. TDD provides a viable option, but imposes precise timing and
synchronization constraints which are needed for data decoding, anyway. However, plain TDD assumes that both
the uplink and the downlink transmissions are performed over the same physical wavelength. This could often be
impractical as visible light emitted by the user terminal may not be desirable. Therefore, the most suitable duplex
technique in Li-Fi is wavelength division duplexing (WDD), where the two communication channels are
established over different electromagnetic wavelengths. Using infrared (IR) transmission is one viable option for
establishing an uplink communication channel. A first commercially-available full duplex Li-Fi modem using IR
light for the uplink channel has recently been announced by pureLiFi. There is also the option to use RF
communication for the uplink. In this configuration, Li-Fi may be used to do the “heavy lifting” and off-load data
traffic from the RF network, and thereby providing significant RF spectrum relief. This is particularly relevant
since there is a traffic imbalance in favor of the downlink in current wireless communication systems.
3.2.3 Summary
The design and construction of the LIFI™ light source enable efficiency, long stable life, full spectrum intensity
and dimming that is digitally controlled and easy to use. With this features 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.
3.3 Working models
Within a local Li-Fi cloud several database 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 to address different user scenarios for wireless indoor and indoor-like data
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transfers. While Giga-Dock is a wireless docking solution including wireless charging for smartphones tablets or
notebooks, with speeds up to 10 Gbps, the Giga-Beam model is a point-to-point 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.
(a) Giga-Dock (b) Giga-Beam
(c) Giga-Shower (d) Giga-MIMO
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Fig 3-6: Giga-Speed usage models (Images courtesy: TriLumina Corp.)
Chapter 4Comparison 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 Li-Fi 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.
Table 1: Comparison between Li-Fi and Wi-Fi
S. No. ParametersWireless Technologies
Light Fidelity Wireless Fidelity
1. Speed for data transfer Faster transfer speed (>1Gbps) Slower transfer speed (150Mbps)
2. Medium through which data transfer occurs
Light is Used as carrier Radio Spectrum is Used as carrier
3. Spectrum range Visible light spectrum has 10,000 time broad spectrum in comparison to radio frequency.
Radio frequency spectrum range is much narrower than visible light spectrum.
4. Cost Cheaper than Wi-Fi because free band doesn’t need license and it uses light.
Expensive in comparison to Li-Fi because it uses radio spectrum which requires license.
5. Network topology Point to point Point to point
6. Operating frequency Hundreds of Tera Hz 2.4 GHz
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 offer 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.
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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 movies, games,
music etc. can be downloaded 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 the
connection is made in case of any light presence. There cannot be anything better than this technology.
Table 2: Comparison between current and future wireless technology
4.1 How is it different?
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 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.
Li-Fi is a term often used to describe high speed VLC in application scenarios where Wi-Fi might also be used.
The term Li-Fi is similar to Wi-Fi with the exception that light rather than radio is used for transmission. Li-Fi
might be considered as complementary to Wi-Fi. If a user device is placed within a Li-Fi hot spot (i.e. under a Li-
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Technology Speed Data Density
Wi-Fi – IEEE802.11n 150 Mbps *
Bluetooth 3 Mbps *
IrDA 4 Mbps ***
Wireless (future)
Wi-Gig 2 Gbps **
Giga-IR 1 Gbps ***
Li-Fi >1Gbps ****
Li-Fi Technology
Fi light bulb), it might be handed over from the Wi-Fi system to the Li-Fi system and there could be a boost in
performance.
Chapter 5Application Areas of Li-Fi Technology
5.1 Airways
Whenever we travel through airways we face the problem
in communication media, because the whole airways
communications are performed on the basis of radio
waves. To overcome this drawback on radio waves, Li-Fi
is introduced.
Fig 5-1: Use of Li-Fi in aeroplane
5.2 Medical applications
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. And, as Haas mentions in his TED Talk, Li-Fi has 10,000 times the
spectrum of Wi-Fi, so maybe we can delegate red light to priority medical data. Code Red!
5.3 In traffic lights
In traffic signals and brake lights Li-Fi can be used which will communicate with the cars and other vehicles and
accidents can be decreased.
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Fig 5-2: Use of Li-Fi in traffic lights
5.4Secure communication
It is very useful to use VLC where a secure and private communication is necessary. In visual light
communication, the node or any terminal attach to our network is visible to the host of network. Blocking the
light and also blocks the signal. However, this is also a potential advantage from a security point of view. Light
cannot penetrate walls as radio signals can, so drive-by hacking of wireless internet signals would be far more
difficult, though not impossible.
5.5 Multi user communications
Li-Fi supports the broadcasting of network. It helps to share multiple things at a single instance called
broadcasting.
5.6 Lightings points used as Hotspot
Any lightings device can be performed as a hotspot. It means that the light device like car lights, ceiling lights,
street lamps etc. all are able to spread internet connectivity using visual light communication which helps us to
use low cost architecture for hotspot. Hotspot is a limited region (usually public places) where a number of
devices can access the internet connectivity. Therefore the internet can be accessed from anywhere if there is any
light source near the end user.
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Fig 5-3: Every light emitting device acting as a Li-Fi Hotspot
5.7 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 implemented solutions, but the draw on a power plant’s own
reserves could be lessened if they haven’t yet converted to LED lighting.
5.8 Undersea awesomeness
Remotely operated underwater vehicles (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 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.
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Fig 5-4: Use of VLC under water
5.9 It could keep people informed and save lives
If there’s an earthquake or a hurricane in a 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. With Li-Fi, if there’s light, they’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.
Chapter 6Advantages over Radio waves
The Li-Fi has the following advantages over RF based technologies.
1. Faster Data Transfer: Li-Fi is much faster than Wi-Fi and other current technologies based on radio spectrum.
2. 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.
3. Unlimited capacity: Visible light is part of the electromagnetic spectrum and 10,000 times bigger than the
radio spectrum, affording potentially unlimited capacity.
4. Availability: Light Source is available everywhere, so possibilities of this technology are very high. Data can
be accessed in home, streets, hospitals, hotels etc.
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5. Efficiency: Li-Fi uses LED lamps which are very energy efficient. This saves a lot of electricity. If 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.
6. High Security: Data can be accessed only if light is available. Light cannot penetrate through walls.
So there is less chance of unauthorized access of data, though it is not impossible.
7. Harmless: Li-Fi is a green information technology unlike radio waves and other communication waves affects
on the birds, human bodies etc. It never gives such side effects on any living thing.
Chapter 7Challenges for Li-Fi
Apart from many advantages over Wi-Fi, Li-Fi technology is facing some challenges. They are:
1. Presence of Light: Presence of light is essential. One can’t access internet if there is no light source. Even on
daytime the lights must be kept on to access data through Li-Fi.
2. Line of Sight: Li-Fi requires direct line of sight. Indoors, one would not be able to shift the receiving device.
This is because visible light can’t penetrate through brick walls or objects as radio waves and is easily blocked by
somebody simply walking in front of LED source.
3. Low efficiency with bulbs: It has higher efficiency with LEDs but very low efficiency with bulbs. So, one has
to use expensive LEDs to get a decent data transmission rate.
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4. Interference with other light sources: Other light sources can easily interfere with Li-Fi thus interrupting data
transmission. When set up outdoors, the apparatus would need to deal with ever changing conditions. Also the
power cord immediately becomes data stream.
5. Not ready for two way communication: Li-Fi works well for one way communication, i.e., the devices can
receive data through it. But in case of two way communication, there is no such well defined and reliable way
how the device will transmit data back.
Chapter 8Conclusion
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 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
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into energy production of 250 nuclear power plants.There are few shortcomings in this technology right now, but
those can be overcome in near future.
Chapter 9References
1. International Journal of advances in computing & communications, vol 1, 2013
http://www.ijacc.org
2. http://en.wikipedia.org/wiki/Li-Fi
3. http://timesofindia.indiatimes.com/home/science/Now-just-light-a-bulb-to-
switch-on-your-broadband/articleshow/9713554.cms
4. http://oledcomm.com/lifi.html
5. http://en.wikipedia.org/wiki/visible_light_communication
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