LI-FI Technical Report

B.Prabhu kiran (11621A0407) AEC, Bhongir

1. INTRODUCTION

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.

Li-fi is transmission of data through illumination by taking the fibre out of fibre 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

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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 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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Fig. 1.1 Li-Fi Environment

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2. HISTORY 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.

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Fig. 2.1 issues regarding Radio 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.

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

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(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 reaching 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 colour 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

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"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.

Fig.2.2 Prof. Harald Hass

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3. WORKING 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.

Fig.3.1 Block Diagram of LI-FI

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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.

3.1 Visible light communication (VLC): A potential solution to the global

wireless spectrum shortage

Li-fi (Light Fidelity) is a fast and cheap optical version of Wi-Fi, the technology of

which is based on Visible Light Communication (VLC).VLC is a data communication

medium, which uses visible light between 400 THz (780 nm) and 800 THz (375 nm) as

optical carrier for data transmission and illumination. It uses fast pulses of light to transmit

information wirelessly. 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

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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-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

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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 fulfil 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.

3.1.1 Multiple accesses 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 super heterodyning. 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.

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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 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,

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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

accesses. This is colour, 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 responsively 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 responsively of photo detector.

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

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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 centre; this controlled plasma generates an intense source

of light. All of these subassemblies are contained in an aluminium 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, 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 super heterodyning 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.

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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 favour 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 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

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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

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b. Giga-Beam

C.Giga-shower

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d. Giga-MIMO

Fig 3-6: Giga-Speed usage models (Images courtesy: TriLumina Corp.)

4. COMPARISON 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.

Table 1: Comparison between Li-Fi and Wi-Fi

S.No Parameters Wireless 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

Radio frequency

spectrum range is

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time broad spectrum

in comparison to

radio frequency

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.

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

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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 ****

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-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.

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5. APPLICATIONS AREAS OF LI-FI TECHNOLOGY

5.1 Air Ways

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

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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!

Fig.5.2 Use of LI-FI in Medical Field

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 5.3 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.

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Fig 5.4 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.

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Fig.5.5 Use of LI-FI in Smart Power Plant

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.5.6 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.

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6. ADVANTAGES 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.

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

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. 6.1(a)

6.1( b)

Fig.6.1 (a&b) Electromagnetic Spectrum

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7. CHALLENGES OF 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.

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.

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8. 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 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. There are few shortcomings in this technology right now, but those

can be overcome in near future.

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9. REFRENCES

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://oledcomm.com/lifi.html

4. http://en.wikipedia.org/wiki/visible_light_communication

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http://en.wikipedia.org/wiki/visible_light_communication

http://oledcomm.com/lifi.html

http://en.wikipedia.org/wiki/Li-Fi

http://www.ijacc.org/

LI-FI Technical Report

Documents