Li-Fi Seminar Report

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

i

Li-Fi Technology

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

ii

Li-Fi Technology

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

1

Li-Fi Technology

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.

2

Li-Fi Technology

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.

3

Li-Fi Technology

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.

4

Li-Fi Technology

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.

5

Li-Fi Technology

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-

6

Li-Fi Technology

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.

7

Li-Fi Technology

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

8

Li-Fi Technology

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

9

Li-Fi Technology

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,

10

Li-Fi Technology

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

11

Li-Fi Technology

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

12

Li-Fi Technology

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.

13

Li-Fi 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

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-

14

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.

15

Li-Fi Technology

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.

16

Li-Fi Technology

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.

17

Li-Fi Technology

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.

18

Li-Fi Technology

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.

19

Li-Fi Technology

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

20

Li-Fi Technology

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

21

Li-Fi Technology

22