LI FI

ABSTRACT

Whether you’re using wireless internet in a coffee shop, stealing it from the guy next door, or competing for bandwidth at a conference, you’ve probably gotten frustrated at the slow speeds you face when more than one device is tapped into the network. As more and more people and their many devices access wireless internet, clogged airwaves are going to make it increasingly difficult to latch onto a reliable signal. But radio waves are just one part of the spectrum that can carry our data. What if we could use other waves to surf the internet?

One German physicist,DR. Harald Haas, has come up with a solution he calls “Data Through Illumination”—taking the fiber out of fiber optics by sending data through an LED light bulb that varies in intensity faster than the human eye can follow. It’s the same idea behind infrared remote controls, but far more powerful. Haas says his invention, which he calls D-Light, can produce data rates faster than 10 megabits per second, which is speedier than your average broadband connection. He envisions a future where data for laptops, smartphones, and tablets is transmitted through the light in a room. And security would be a snap—if you can’t see the light, you can’t access the data.

CONTENTS

1. INTRODUCTION TO LI-FI 4

2. GENESIS OF LI-FI 6

3. HOW LI-FI WORKS 7

4. WHY LI-FI? 10

4.1 PRESENT SCENARIO IN WIRELESS COMMUNICATION 10

4.2 ISSUES WITH WI-FI USING RADIO WAVES 10

4.3 ALTERNATIVES TO RADIO WAVES IN EM SPECTRUM 11

5. LIGHT FOR WIRELESS COMMUNICATION 13

6. POTENTIAL APPLICATIONS OF LI-FI 14

7. ADVANTAGES AND DISADVANTAGES OF LI-FI 15

8. FUTURE 16

9. CONCLUSION 17

10. REFERENCES 18

INTRODUCTION TO LI-FI

WHAT IS LI-FI?

Li-Fi is a VLC, visible light communication, technology developed by a team of scientists including Dr Gordon Povey, Prof. Harald Haas and Dr Mostafa Afgani at the University of Edinburgh. The term Li-Fi was coined by Prof. Haas when he amazed people by streaming high-definition video from a standard LED lamp, at TED Global in July 2011. Li-Fi is now part of the Visible Light Communications (VLC) PAN IEEE 802.15.7 standard.

“Li-Fi is typically implemented using white LED light bulbs. These devices are normally used for illumination by applying a constant current through the LED. However, by fast and subtle variations of the current, the optical output can be made to vary at extremely high speeds. Un-seen by the human eye, this variation is used to carry high-speed data,”

says Dr Povey, , Product Manager of the University of Edinburgh's Li-Fi Program ‘D-Light Project’. 

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 mil-lions 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 infrastruc-ture, 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 focus-ing on parallel data transmission using arrays of LEDs, where each LED trans-mits 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 differ-ent 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.

GENESIS OF LI-FI

fig. 2.1 DR. Harald Hass, at TED Talks July 2011

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 TEDGlobal conference in Edinburgh on 12th July 2011. He used a table lamp with an LED bulb to transmit a video of blooming flowers that was then projected onto a screen behind him. During the event he periodically blocked the light from lamp to prove that the lamp was indeed the source of incoming data.

At TEDGlobal, Haas demonstrated a data rate of transmission of around 10Mbps -- comparable to a fairly good UK broadband connection. Two months later he achieved 123Mbps. 

HOW LI-FI WORKS?

Fig. 3.1 Data transfer using Li-Fi.

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.  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, you transmit a digital 1, if it’s off you transmit a 0. The LEDs can be switched on and off very quickly, which gives nice opportunities for transmitting data. 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. 3.2 An artistic future vision of Li-Fi system at work.

To further get a grasp of Li-Fi consider an IR remote.(fig 3.3). 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, fig 3.4, is capable of sending thousands of such streams at very fast rate.

Fig 3.3 , Data stream from an IR remote control.

Fig 3.4 , Data streams of a typical Li-Fi system

WHY LI-FI?

PRESENT SCENARIO IN WIRELESS COMMUNICATION

There are 1.4 million cellular radio masts deployed worldwide.

There are more than five billion wi-fi devices present.

With all these devices, we transmit more than 600 terabytes of data every month.

Wireless communications has become a utility like electricity and water. We use it every day. We use it in our everyday lives now -- in our private lives, in our business lives. And we even have to be asked sometimes, very kindly, to switch off the mobile phone at events like this for good reasons. And , therefore , it is very important to look into the issues that this technology has, because it's so fundamental to our lives.

ISSUES WITH WI-FI USING RADIO WAVES

There are four issues with the current wi-fi scenario , which are :-

1. CAPACITY

We transmit wireless data is by using electromagnetic waves -- in particular, radio waves.

Radio waves are scarce, expensive and we only have a certain range of it.

Due to this limitation one can’t forever hope to cope with the demand of wireless data transmissions and the number of bytes and data which are transmitted every month.

2. EFFICIENCY

There are 1.4 million cellular radio masts deployed worldwide.

Most of the energy consumed, is not used to transmit the radio waves, but is used to cool the base stations.

The efficiency of such a base station is only at about five percent.

3. HEALTH ISSUES

There are potential health issues associated with radio waves.

Consequently we have to switch off devices like cell-phones in places like hospitals.

4. SECURITY

 The radio waves penetrate through walls.

They can be intercepted, and somebody can make use of one’s network.

ALTERNATIVES TO RADIO WAVES IN EM SPECTRUM

The issues concerning radio waves begs a close inspection at EM Spectrum for some alternative. The EM Spectrum is as given below :-

Fig. 4.1 The Electromagnetic Spectrum

Gamma Rays can’t be used as they could be dangerous.

X-Rays have similar health issues.

Ultraviolet Light is good for a nice suntan, but otherwise dangerous for the human body.

Infrared , due to eye safety regulations, can only be used with low power.

Hence we are left with only the Visible Light Spectrum.

LIGHT FOR WIRELESS COMMUNICATION

Light is inherently safe and can be used in places where radio frequency communication is often deemed problematic, such as in aircraft cabins or hospitals. So visible light communication not only has the potential to solve the problem of lack of spectrum space, but can also enable novel application. The visible light spectrum is unused, it's not regulated, and can be used for communication at very high speeds.

HOW LI-FI OVERCOMES ISSUES ATTACHED WITH RADIO WAVES :-

1. CAPACITY

We have 10,000 times more spectrum in visible light region than in the radio waves region.

Therefore we have 10,000 times more channels to transmit data.

2. EFFICIENCY

LED consumes very little power therefore the data transmission is very efficient.

3. SAFETY

Visible light poses no health issues.

4. SECURITY

Light Waves doesn’t penetrate through walls.

Therefore they can’t be intercepted easily.

POTENTIAL APPLICATIONS OF LI-FI

Li-Fi technology is still in it’s infancy. However some areas where it seems perfectly applicable are :-

1. TRAFFIC LIGHTS

Traffic lights can communicate to the car and with each other.

Cars have LED-based headlights, LED-based back lights, and cars can communicate with each other and prevent accidents in by exchanging information. 

2. INTRINSICALLY SAFE ENVIRONMENTS

Visible Light is more safe than RF, hence it can be used in places where RF can’t be used such as petrochemical plants, airplanes etc.

3. PUBLIC INTERNET HOTSPOTS

There are millions of street lamps deployed around the world.

Each of these street lamps could be a free access point.

4. ON OCEAN BEDS

Li-Fi can even work underwater where Wi-Fi fails completely, thereby throwing open endless opportunities for military/navigation operations.

ADVANTAGES/DISADVATAGES OF LI-FI

ADVANTAGES

1. SUPERIORITY OVER RF WAVES

As was demonstrated earlier, the visible light has considerable edge over RF waves in many fields.

2. LITTLE INFRASTRUCTURE REQUIREMENTS

There are an estimated 14 billion bulbs in the world today. Since Li-Fi can operate

on conventional LEDs infrastructure is pretty much present already.

3. SIMPLE SYSTEM STRUCTURE

A typical Li-Fi system consists of an LED array, a photoreciever , a de/modulator pair.

DISADVANTAGES

The biggest disadvantage is that it needs direct line of sight to transmit data, so one wouldn't be able to have a single router in his/her house and the data goes through walls etc..

FUTURE

In 2009, the US Federal Communications Commission warned of a looming spectrum crisis: because our mobile devices are so data-hungry we will soon run

out of radio-frequency bandwidth. Li-Fi could free up bandwidth, especially as much of the infrastructure is already in place.

The solution might be Li-Fi. Direct modulation of LED devices is a low cost, secure, and safe way to transmit data, and there is an abundance of free visible light spectrum.  High intensity LEDs used in light bulbs, flash lights and cameras can transmit very high data rates, faster than Wi-Fi.

And the technique looks good not only on paper. At Heinrich Hertz Institute in Berlin, Germany researchers have achieved a data rate of 500 megabytes per second using a standard white LED. This year’s,2012, Consumers Electronics Show in Las Vegas demonstrated VLC in full vigour when a pair of Casio smartphones exchanged data using light of varying intensity given off from their screens. In October, 2011 a number of companies and industry groups formed the Li-Fi Consortium to work towards and promote Light Fidelity (Li-Fi) in order to overcome the rapidly diminishing bandwidth for Wireless Fidelity (Wi-Fi). 

However everyone is not so optimistic. Dr Suresh Borkar , a trend-watcher, consul-tant and communications expert who teaches at the Illinois Institute of Technology, opines that at the current stage of maturity, Li-Fi usage will be limited to in-house and proximity applications. The use of very high frequency (400-800 THz) limits it to very short distances and more of point-to-point communications.Li-Fi, according to Dr Borkar, is still in the experimental laboratory stage. Stan-dards have to be defined and devices identified and made available along with the infrastructure and related entities before it can be used widely. Some limited proto-typefriendly deployments have taken place in the last year or so but the availability of receiving devices that require arrays of photodiodes is still limited.

CONCLUSION

The fact that Li-Fi is being considered as one of the IEEE 802.xx standards bodes well for its potential success. Like other 802.xx standards, it is defined only at lay-ers 1 and 2 (physical and media access control (MAC) layers) of the Open Systems Interconnection (OSI) model. Layer 3 and higher layers need to be designed using the Internet Engineering Task Force (IETF) packet transport standards.

Li-Fi is certainly not useless, but it has certain inherent limits for the technology. LiFi may not be able to replace conventional radios altogether, but it could tur-bocharge the development of wireless television and make it easier to throw a wireless signal across an entire house. At present, finding the ideal position for a wireless router is something of a divine art. If the signal could be passed via VLC from Point A to Point B inside a home, small local routers at both points could cre-ate local fields with less chance of overlapping and interfering with each other. Large scale areas that are saturated with radio signals or that don’t permit them for security reasons could use LiFi as an alternate high-speed wireless network solu-tion.

BIBLIOGRAPHY

REFERENCES

[1] Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [Visible Light Communication : Tutorial]

Date Submitted: [9 March 2008]

Source: [(1)Eun Tae Won, Dongjae Shin, D.K. Jung, Y.J. Oh, Taehan Bae, Hyuk-Choon Kwon, Chihong

Cho, Jaeseung Son, (2) Dominic O’Brien (3)Tae-Gyu Kang (4) Tom Matsumura] Company [(1)Samsung

Electronics Co.,LTD, (2)University of Oxford, (3)ETRI (4) VLCC (28 Members)]

[2] Design and Implementation of an Ethernet-VLC Interface for Broadcast

Transmissions

Thispaper appears in: Communications Letters, IEEEDate of Publication: December 2010Author(s): Delgado, F. Dept. de Ingeniera Telematica, Univ. de Las Palmas de Gran Canada, Las Palmas de Gran, Spain Quintana, I. ;  Rufo, J. ;  Rabadan, J.A. ;  Quintana, C. ;  Perez-Jimenez, R. 

Websites

http://www.ed.ac.uk

http://www.visiblelightcomm.com

http://new.electronicsforu.com

http://blog.ted.com

http://www.newscientist.com

http://purevlc.com