‘Li-Fi TECHNOLOGY’

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ABSTRACT

Whether you‘re using wireless internet in a coffee shop, stealing it from the guy next door, or

competing for bandwidth at a conference, you’ve probably gotten frustrated at the slow

speeds you face when more than one device is tapped into the network. As more and more

people and their many devices access wireless internet, clogged airwaves are going to make it

increasingly difficult to latch onto a reliable signal. But radio waves are just one part of the

spectrum that can carry our data. What if we could use other waves to surf the internet?

One German physicist DR. Harald Haas has come up with an idea and he calls it Li-Fi. He

envisions a future where data for laptops, smart phones and tablets is transmitted through the

light in a room. Light Fidelity (Li-Fi) is a bidirectional, high speed, fully networked wireless

communication technology similar to Wi-Fi. It is a form of visible light communication.

By 2020 44 zeta bytes of data will be generated and 80 billion Internet of Things devices will

be connected to the internet. The current wireless technology will not able to handle so much

of data. Thus we need to explore and see if we can use visible light for communication.

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CONTENTS

1. Wi-Fi 8

2. Need For Li-Fi 11

3. History Of Li-Fi 14

4. Working Of Li-Fi 15

5. Li-Fi Products 18

6. Solar Li-Fi 22

7. Applications Of Li-Fi 24

8. Limitations Of Li-Fi 28

9. Conclusion 29

References

Appendix

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LIST OF FIGURES

Fig-1: Cellular radio base station and Mobile phone 11

Fig-2: Electromagnetic Spectrum 12

Fig-3: Professor Harald Hass 14

Fig-4: Transmission using Li-Fi 15

Fig-5: block diagram of Li-Fi 16

Fig-6: Li-Fi system connecting devices in a room 17

Fig-7: Li-1st 18

Fig -8: Block diagram of Li-1st 19

Fig-9: Li Flame 20

Fig -10: Li-Flame ceiling unit 21

Fig-11: Li-Flame desktop unit 21

Fig-12: Solar Li-Fi 22

Fig- 13: Li-Fi in aircraft 24

Fig- 14: Li-Fi in under water 25

Fig- 15: Li-Fi in power plants 25

Fig- 16: Li-Fi in traffic management 26

Fig- 17: Li-Fi in hospitals 27

Fig-18: Li-Fi in shops 27

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LIST OF ABBREVATIONS1. VLC-Visible Light Communication

2. Li-Fi-Light Fidelity

3. Wi-Fi-Wireless Fidelity

4. LED-Light Emitting Diode

5. IR-Infrared Ray

6. OFDM-orthogonal frequency division multiplexing

7. OOK-On Off Keying

8. FHSS-Frequency Hop Spread Spectrum

9. DSSS-Direct Sequence Spread Spectrum

10. QAM-Quadrature Amplitude Modulation

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CHAPTER 1

Wi-Fi

Wi-Fi is a technology that allows electronic devices to connect to a wireless local area

network (WLAN) mainly using the 2.4 gigahertz (12 cm) and 5 gigahertz (6 cm)  radio

bands. A WLAN is usually password protected, but may be open, which allows any device

within its range to access the resources of the WLAN network. The Wi-Fi Alliance defines

Wi-Fi as any "wireless local area network" (WLAN) product based on the IEEE 802.11

standards.

Devices which can use Wi-Fi technology include personal computers, video-game consoles,

smart phones, digital cameras, tablet computers, digital audio players and modern printers.

Wi-Fi compatible devices can connect to the Internet via a WLAN network and a wireless

access point.  Such an access point has a range of about 20 meters (66 feet) indoors and a

greater range outdoors. Hotspot coverage can be as small as a single room with walls that

block radio waves, or as large as many square kilometres achieved by using multiple

overlapping access points. Wi-Fi is less secure than wired connections because an intruder

does not need a physical connection.

The IEEE 802.11 standard is a set of media access control (MAC) and physical layer (PHY)

specifications for implementing wireless local area network (WLAN) computer

communication. The base version of the standard was released in 1997, and has had

subsequent amendments. The standard and amendments provide the basis for wireless

network products. 802.11-1997 was the first wireless networking standard in the family, but

802.11b was the first widely accepted one, followed by 802.11a, 802.11g, 802.11n, and

802.11ac. The frequency used is either 2.4 GHz or 5 GHz.The maximum speed has been

constantly improving.802.11a could achieve a maximum speed of 54 Mbps.Theoretically

802.11n and 802.11 ac can reach a speed of 600 Mbps and 1.3Gbps respectively

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Protocol Frequency Signal Max. Data Rate

Legacy 802.11 2.4 GHz FHSS or DSSS 2 Mbps

802.11a 5 GHz OFDM 54Mbps

802.11b 2.4 GHz HR-DSSS 11Mbps

802.11g 2.4 GHz OFDM 54Mbps

802.11n 2.4 or 5 GHz OFDM 600Mbps

802.11ac 5 GHz 256-QAM 1.3Gbps

The various modulation techniques that have been used are:

1: FHSS-Frequency Hop Spread Spectrum

Frequency Hopping Spread Spectrum (FHSS) is a method of transmitting radio signals by

rapidly switching a carrier among many frequency channels using a pseudorandom sequence

known to both transmitter and receiver.

2: DSSS-Direct Sequence Spread Spectrum

 Direct-sequence spread spectrum (DSSS) is a spread spectrum modulation technique. Spread

spectrum systems are such that they transmit the message bearing signals using a bandwidth

that is in excess of the bandwidth that is actually needed by the message signal.

3: OFDM- Orthogonal frequency-division multiplexing 

It is a method of encoding digital data on multiple carrier frequencies.  A large number of

closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data

streams. Each sub-carrier is modulated with a conventional modulation scheme 

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4: QAM-Quadrature Amplitude Modulation

Quadrature amplitude modulation (QAM) is both an analog and a digital modulation scheme.

It conveys two analog message signals or two digital bit streams by changing the amplitude

of two carrier waves using amplitude shift keying digital modulation scheme or amplitude

modulation analog modulation scheme.

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CHAPTER 2

Need For Li-Fi

We have 1.4 million cellular radio masts deployed worldwide. And these are base

stations. And we also have more than five billion of these devices here.These are cellular

mobile phones. And with these mobile phones, we transmit more than 600 terabytes of

data every month.

Fig-1: Cellular radio base station and Mobile phone

The main issues facing wireless communication using radio waves are:

1. Capacity

2. Efficiency

3. Availability

4. Security

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 The radio waves are limited. They are scarce; they are expensive; and we only have a certain

range of it.Thus capacity is an issue.  1.4 million cellular radio masts, or base

stations, consume a lot of energy.

 Most of the energy is not used to transmit the radio waves; it is used to cool the base stations.

Then the efficiency of such a base station is only at about five per cent. We have to switch off

our mobile phones in aircrafts. In petro chemical plants radio waves cannot be used. Radio

waves are not available everywhere. Security is another issue. These radio waves penetrate

through walls. They can be intercepted, and somebody can make use of your network if he

has bad intentions.

Fig-2: Electromagnetic Spectrum

Thus it is clear that although wireless communication using radio waves is very useful there

are some issues with it.Radio waves are just one part of the electromagnetic spectrum. Let us

see if we can use other waves for communication. Gamma rays are harmful and we cannot

use them. X-rays can be used in hospitals but not much beyond that. Ultra violet rays are

dangerous for human body. Infra- red rays can be used only in low power applications due to

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eye safety regulations. But we have visible light ranging from 400 THz to 800 THz. Let us

see the advantages we will have if we use visible light for communication (VLC).

Advantages of using visible light for communication

Due to a bandwidth of almost 400 THz we can solve the capacity issue using visible light

communication. We have 10,000 times more spectrum when compared to radio waves.

This is data through illumination -- it's first of all an illumination device. So if we can

combine data transfer and illumination it would be great. Also led light bulbs have high

energy efficiency.

Light is available in aircrafts and hospitals. Light is available everywhere. Thus there is no

more availability issue. Light does not penetrate walls. Hence Li-Fi is more secure than Wi-

Fi. So thus it is clear that there is immense potential in visible light communication.

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CHAPTER 3

HISTORY OF Li-Fi

The idea of Li-Fi was introduced by a German Physicist Prof.Harald Haas; in his TED Global

talk in 2011.It was in this talk that Li-Fi was demonstrated for the first time.

Fig-3: Professor Harald Hass

He used a table lamp with an LED bulb to transmit a video of blooming flowers that was then

projected onto a screen behind him. During the event he periodically blocked the light from

lamp to prove that the lamp was indeed the source of incoming data.

PureLiFi was established in 2012 as VLC ltd. It aims to develop and deliver Li-Fi solutions.

They have successfully launched 3 Li-Fi products. They are Li-1st, Li- Flame, LiFi- X. In

2015 solar Li-Fi was demonstrated. Solar cells were used as Li-Fi receivers.

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CHAPTER 4

WORKING OF Li-Fi

An LED is a semiconductor. It's an electronic device. And it has a very nice acute

property. Its intensity can be modulated at very high speeds, and it can be switched off at

very high speeds. And this is a fundamental basic property that we exploit with our

technology.

Remote controls have an infrared LED. It creates a simple, low-speed data stream in 10,000

bits per second or 20,000 bits per second. We transmit with our technology, not only a single

data stream; we transmit thousands of data streams in parallel, at even higher speeds using Li-

Fi.

Fig-4: Transmission using Li-Fi

The operational procedure is very simple, if the LED is on, you transmit a digital 1, if it’s off

you transmit a digital 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. We have to just vary the rate at which the LED’s flicker

depending upon the data we want to encode.

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Fig-5: block diagram of Li-Fi

When a constant current is applied to an LED light bulb a constant stream of photons are

emitted from the bulb which is observed as visible light. If the current is varied slowly the

output intensity of the light dims up and down. Because LED bulbs are semi-conductor

devices, the current, and hence the optical output, can be modulated at extremely high speeds

which can be detected by a photo-detector device and converted back to electrical current.

The intensity modulation is imperceptible to the human eye, and thus communication is just

as seamless as RF. Using this technique, high speed information can be transmitted from an

LED light bulb.

Since Li-Fi uses visible light for sending data, it is necessary to modulate the data into a

signal which can be transmitted. One possible modulation technique is OOK.On-off keying

(OOK) denotes the simplest form of amplitude-shift keying (ASK) modulation that represents

digital data as the presence or absence of a carrier wave. In its simplest form, the presence of

a carrier for a specific duration represents a binary one, while its absence for the same

duration represents a binary zero.

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Fig-6: Li-Fi system connecting devices in a room.

The above figure shows how Li-Fi can be implemented. The LED bulbs shown in the figure

are not just illuminating devices alone. They can transfer data as well. Using this we can

access the internet from our mobiles, computer and laptops.

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CHAPTER 5

Li-Fi PRODUCTS

5.1: Li-1st

Fig-7: Li-1st

This is the world’s first Li-Fi system. It offers full duplex communication with a capacity

up to 5Mbps downlink and 5Mbps uplink. It has a range of up to 3 meters. It has ceiling

unit and desktop unit.

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Li-1st Ceiling Unit

It is connected to the data network via a standard Ethernet RJ45 port.

It encodes the data and transmits it by modulating the intensity of the LED light. The Li-

1st ceiling unit receives and decodes the uplink signal using an infra-red detector and

optics.

Fig -8: Block diagram of Li-1st

Li-1st desktop unit

The desktop unit has a visible light decoder captures the continuous sequence of light

intensity changes. It then decodes the binary stream and transmits it to the client device via

an USB connection. The desktop unit receives data from the client device, encodes it and

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transmits it to the ceiling unit using an infra-red emitter. The receiver is very sensitive. It

can operate even using reflected light.

5.2: Li-Flame

The Li-Flame is the world’s first high-speed wireless network solution using VLC. There

are multiple APs (access point) throughout an indoor space allow users to move from one

AP to the next AP.There is no interruption in its high-speed data stream.

Fig-9: Li Flame.

Li-Flame ceiling unit

Data and power via standard Ethernet port

Simple installation

Connects to an LED light fixture to form an atto-cell over a wide area

Multiple access

Handover control enables seamless switching between Aps

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Li-Flame Desktop Unit

Connects to client device via USB

10Mbps infrared uplink to ceiling unit

Handover capable, allowing user to move from one AP to the next without losing the

high-speed data connection

Transceiver swivel head can be adjusted by user to optimise the connection

Battery-powered and portable

Fig -10: Li-Flame ceiling unit

 

 

Fig-11: Li-Flame desktop unit.

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CHAPTER 6

SOLAR Li-Fi

There will be a massive extension of the Internet to close the digital divide, and also to

allow for what we call "The Internet of Things" -- tens of billions of devices connected to

the Internet. Such an extension of the Internet can only work if it's almost energy-

neutral. This means we need to use existing infrastructure as much as possible. And this is

where the solar cell and the LED come in.It is possible to transmit a video from a standard

off-the-shelf LED lamp to a solar cell with a laptop acting as a receiver.

Fig-12: Solar Li-Fi

A solar cell absorbs light and converts it into electrical energy. This is why we can use a

solar cell to charge our mobile phone. But now we need to remember that the data is

encoded in subtle changes of the brightness of the LED, so if the incoming light

fluctuates, so does the energy harvested from the solar cell. This means we have a

principal mechanism in place to receive information from the light and by the solar cell,

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because the fluctuations of the energy harvested correspond to the data transmitted. Of

course the question is: can we receive very fast and subtle changes of the brightness, such

as the ones transmitted by LED lights? And the answer to that is yes, we can.

In 2015, Harald Haas demonstrated the use of solar cells as Li-Fi receivers.  A solar cell has

become a receiver for high-speed wireless signals encoded in light, while it maintains its

primary function as an energy-harvesting device. That's why it is possible to use existing

solar cells on the roof of a hut to act as a broadband receiver from a laser station on a close by

hill, or indeed, lamp post.

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CHAPTER 7

APPLICATIONS OF Li-Fi

7.1: Aircrafts

Fig- 13: Li-Fi in aircraft

Wi-Fi is not used in aircrafts because it may interfere with the navigation system of pilots.

The light available in aircrafts can be used for data transmission. Thus it is possible that

passengers can watch online videos during long flights.

7.2: Under water applications

Under water ROVs (Remote Operated Vehicles) operate from large cables that supply

power and allow them to receive signals from above. But the tether is not long enough to

allow them to explore large areas. If their wires were replaced with light-say from a

submerged, high powered lamp-then they would be freer to explore.

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Fig- 14: Li-Fi in under water

7.3: Power Plants

Fig- 15: Li-Fi in power plants

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Power plants need fast data systems to monitor important parameters. Radio waves cannot

be used because they will cause interference. Here Li-Fi offers safe, abundant connectivity

for all areas of these sensitive locations.

7.4: Traffic Management

Fig- 16: Li-Fi in traffic management.

In traffic signals Li-Fi can be used for communication with LED light of cars. Also LED

lights of 2 cars can communicate with each other. This can help in better traffic management

and reduce the number of accidents.

7.5: Medical Applications

Operation theatres do not allow Wi-Fi due to radiation concerns. To overcome this and to

make OT tech savvy Li-Fi can be used to access internet and to control medical

equipment’s. This can be even beneficial for robotic surgeries and other automated

procedures.

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Fig- 17: Li-Fi in hospitals.

7.6: In shops

Fig-18: Li-Fi in shops

Shopkeepers can use Li-Fi to communicate with customers. This is an innovative technique.

They can display details of their products like the cost, discount rate and so on. This would

enhance the shopping experience of the customers

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CHAPTER 8

Limitations of Li-Fi

One of the major demerits of this technology is that light cannot penetrate into the walls and

other materials which radio waves can do. Thus the signal will be contained to one area.

Using Li-Fi technology to achieve ideal speeds direct line of sight may be required. Line-of-

sight means the photo detectors have to be able to actually see the light in order to capture the

data.

Another major challenge facing Li-Fi technology is how the receiving device will transmit

back to transmitter. In Li-Fi products like Li-Flame infrared rays had to be used for uplink

communication.

Interferences from external light sources like sun light, normal bulbs, and opaque materials in

the path of transmission can cause interruption in the communication.

Thus it is clear that Li-Fi technology has some limitations. Still Li-Fi could emerge as a boon

to the rapidly depleting bandwidth of radio waves.Li-Fi is not going to replace Wi-Fi but it is

an effective technology which can be used along with Wi-Fi.

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CHAPTER 9

CONCLUSION

Li-Fi has great potential in the field of wireless data transmission. It has the ability to

revolutionise wireless communication in the future.

Using Li-Fi we aim to combine two basic functionalities-illumination and wireless data

transmission. This could solve the four essential problems that face us in wireless

communication these days.

Every light source has the potential to be a hub for data transmission. In the future data for

laptops, smartphones could be transmitted through the light in the room.

Thus Li-Fi has the potential to lead us to a cleaner, greener and maybe just a brighter future.

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REFERENCES

1. Harald Haas, Member, IEEE, Liang Yin, Student Member, IEEE, Yunlu Wang, Student

Member, IEEE , and Cheng Chen, Student Member, IEEE ,“What is LiFi?”, Journal Of Light

wave Technology,2015

2. Shubham Chatterjee, Shalabh Agarwal, Asoke Nath “Scope and Challenges in Light

Fidelity (LiFi) Technology in Wireless Data Communication”, International Journal of

Innovative Research in Advanced Engineering (IJIRAE), Issue 6, Volume 2 (June 2015)

3. Nitin Vijaykumar Swami,” Li-Fi (LIGHT FIDELITY) – THE CHANGING SCENARIO

OF WIRELESS COMMUNICATION”, IJRET: International Journal of Research in

Engineering and Technology, 2015

4. http://www.lifi.eng.ed.ac.uk/

5. http://purelifi.com/

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