DATA TRANSMISSION THROUGH VISIBLE LIGHT

7/30/2019 DATA TRANSMISSION THROUGH VISIBLE LIGHT

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International Journal of Electronics,Communication & Instrumentation Engineering

Research and Development (IJECIERD)

ISSN 2249-684XVol. 2 Issue 4 Dec 2012 81-88

TJPRC Pvt. Ltd.,

DATA TRANSMISSION THROUGH VISIBLE LIGHT

1RASTE MADHURA M,

2GHADIGAONKAR AMIT H

&

2THARA RAFAT A

1Assistant Professor, Annasaheb Dange College of Engineering & Technology, Ashta, Sangli, Maharastra, India

2B.E Electronics and Telecommunication, Annasaheb Dange College of Engineering & Technology, Ashta, Sangli,

Maharastra, India

ABSTRACT

What if every light bulb in the world could also transmit data? Consider the amount of light bulbs that are already

installed in the world. And the amount of energy they consume. If this can be used to transmit data, consider the amount of

energy saved.

In an age where we face a challenge of data congestion in the free air medium, where we strive hard to squeeze in

all the data in the allocated spectrum. Thats when we need to think a bit out of the box, look around us an what we see is a

visible light spectrum, the thing that exists everywhere.

Something we generally use every day, there is not a single area where we do not need light.

With this emerging technology we can use all the light around us that we produce to transmit data, data in the

form of bits and bytes. Considering a the amount of dependency that we have in the present world on the use of cell phones

or laptops or the internet it is a need of the present world that we check alternate ways to transmit all this huge amount of

data we generally use.

By flickering the light from a single LED, a change too quick for the human eye to detect, they can transmit far

more data than a cellular tower using SIM OFDM technique-- and do it in a way that's more efficient, secure and

widespread.

In our paper we aim to give a glimpse of the possibilities of all that we can do with the visible light. We aim to

present the scope of this technology in near future.

KEYWORDS: Data Transmission, Light Bulbs, Flickering, LED, SIM, OFDM Technique

INTRODUCTION

Wireless optical communications has been used long before radio communications was first considered. However,

over the last century radio communication has been the preferred means to transmit data wirelessly. Only now when we are

faced with capacity shortages for wireless data communications is free-space optical communication being considered as a

candidate for widespread wireless communications applications. With the widespread use of LED light bulbs, visible light

communications has become the forerunner in the current optical wireless communications field. Fraunhofer heinrich hertz

institute reached speeds of 800 megabits per second (Mbit/s) working with red green blue (RGB) LEDs, and speeds of 500

Mbit/s with white light LEDs.

History

The history of Visible Light Communications (VLC) dates back to 1880 when Scottish born Canadian Alexander

Graham Bell demonstrated the Photophone which transmitted speech on modulated sunlight over several hundred meters.

It is interesting to note that this actually pre-dates the transmission of speech via radio.


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82 Raste Madhura M., Ghadigaonkar Amit H.& Thara Rafat A.

In January 2010 a team of researchers from Siemens and Fraunhofer Institute for Telecommunications (Heinrich

Hertz Institute in Berlin) demonstrated transmission at 500 Mbit/s with a white LED over a distance of 5 metres (16 ft),

and 100 Mbit/s over longer distance using five LEDs.In December 2010 St. Cloud, Minnesota was the first to

commercially deploy this technology.In July 2011 a live demonstration of high definition video being transmitted from a

standard LED lamp was show at TED Global.

Figure 1

Drawbacks of Current Wireless System

Availability

Even though current wireless system promises the large coverage area they are not available in remote areas. In

remote area planting a base station is not affordable for communication companies. Hence availability of RF

communication is having limitations.

Efficiency

Do you know that 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 RF cellular mast consume lot of energy. Most of the

energy is not used to transmit data but to cool the base stations. These cellular mast have efficiency only up to 5%.Hence

RF communication is inefficient.

Capacity

With these mobile phones, we transmit more than 600 terabytes of data every month. And wireless

communications has become a utility like electricity and water. 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 it's this importance why I decided to look into the issues that this technology has, because it's so

fundamental to our lives. But the problem with RF communication is of limited bandwidth, hence it running out of

capacity.

Security

Radio waves Radiofrequency can penetrate through wall and hence it can be hacked. Wi-Fi networks that are

open (unencrypted) can be monitored and used to read and copy data transmitted over the network, unless another security

method is used to secure the data, such as a VPN or a secure web page.


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Data Transmission through Visible Light 83

Other

Information conveyed through electric field, signal is complex valued and bipolar unlike VLC which sends

information through light, is real valued and unipolar.

Visible Light Communication (VLC)

Visible light is the form in which electromagnetic radiation with wave lengths in a particular range is interpreted

by the human brain. Visible light is thus by dentition comprised of visually-perceivable electromagnetic waves. The visible

spectrum covers wave lengths from 380 nm to 750 nm shows for each wave length the associated colour tone as perceived

byhuman beings. This is 10000 times that of radio spectrum.

Edinburgh start-up Visible Light Communications (VLC) is focussing on using flickering LEDs instead of Wi-Fi

for broadband communications.

Speeds of up to 800Mbits/sec have been achieved for the technology, called Li-Fi, but the first product from VLC

- a consumer transmitter - will deliver data at 100Mbits/sec using VLC's SIM-OFDM technology and optical spatial

modulation.

The technology was invented by Edinburgh University's Harald Haas. This emerging technology provides optical

wireless

Communication (OLC) by using visible light. Today it is seen as an alternative to different RF-based

communication services in wireless personal-area-networks. An additional opportunity is arising by using current state-of-

the-art LED lighting solutions for illumination and communication at the same time and with the same modulethis can be

done due to the abilityto module LEDs at speeds for faster than the human eye can detect while still providing artificial

lightning.

Figure 2

Basic Block Diagram

Technologies used

Visible light communication (VLC) is a fascinating and emerging communication technology employing visible

light with spectrum between 400 THz and 790 THz for both illumination and data communication. Signal is transmitted

with LED (about 10 Mbps) by their intensity modulations. Several modulation techniques could be adopted e.g. on/off

keying (OOK) which is the main output for the system. The VLC uses LEDs to send data by flashing light at undetectable


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speeds to human eyes. Its applications can be found in office broadband communications, secured communications, hybrid

energy and communications, and smart home.

Devices used for Visible Light Communication

Figure 3

Transmitters: Every kind of light source can theoretically be used as transmitting device forVLC or LI-FI. However,

some are better suited than others. For instance, incandescentlights quickly break down when switched on and off

frequently. These are thus not recommended as VLC transmitters. More promising alternatives are LEDs. VLC

transmitters are usually also used for providing illuminationof the rooms in which they are used. The simplest form of

LEDs is those which consist of a bluish to ultraviolet LEDsurrounded by phosphorus which is then stimulated by the actual

LED and emitswhite light. This leads to data rates up to 40 Mbit/s. RGB LEDs do not rely on phosphorus any more to

generate white light.

They come with three distinct LEDs (a red, a blue and a green one) which, when lightingup at the same time, emit

light that humans perceive as white, because there is no delay by stimulating phosphorus. Data rates of up to 100 MBits/s

can be achieved using RGB LEDs. In recent years the development of resonant cavity LEDs (RCLEDs) has

advancedconsiderably. These are similar to RGB LEDs in that they are comprised of threedistinct LEDs, but in addition

they are fitted with Bragg mirrors which enhancethe spectral clarity to such a degree that emitted light can be modulated at

very high frequencies. In early 2010, Siemens has shown that data transmission at a rate of 500MBit/s is possible with this

approach.

Receivers: The most common choice of receivers is photodiodes which turn light into electrical pulses. The signal

retrieved in this way can then be demodulated into actualdata. In more complex VLC-based scenarios, such as Image

Sensor Communicationeven CMOS or CCD sensors are used (which are usually built into digital cameras).

Modulation Techniques

In order to actually send out data via LEDs, such as pictures or audio, it is necessary to modulate these into a

carrier signal. In the context of visible lightcommunication, this carrier signal consists of light pulses sent out in short

intervals.How these are exactly interpreted depends on the chosen modulation scheme, twoof which are

1. Subcarrierpulse {position modulation} is presented which is already established as VLC-standard bythe VLCC.2. The second modulation scheme to be addressed is called frequency shiftkeying(FSK)a) Pulse-position modulation:Sub-Carrier Inverse PPM (SCIPPM), method whose structure is divided into two

parts, sub-carrier part and DC part. The DC part is only for lighting or indicating. If lighting or indicating is not needed,

SCPPM (Sub-Carrier PPM) is used for VLC as shown in Fig 4. to save energy.


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SCIPPM Sub-Carrier PPM

Figure 4

b) Frequency {shift keying}: In frequency shift keying (FSK) data is represented by varying frequencies of thecarrier wave. In order to transmit two distinct values (0 and 1), there need tobe two distinct frequencies. This is also the

simplest form of frequency {shift keying, called binary frequency shift keying (BFSK)}.

SIM-OFDM Technique

Figure 5

Above shown is the basic OFDM technique. Where wideband is divided in subcarrier to transmit data is a method

for dividing wideband channel into independent narrowband sub channels.

Then, the sub-channels (subcarriers) are used in parallel to form what so called multicarrier communication, see

Fig.5

Unlike traditional OFDM depicted in Fig.5 the SIM OFDM technique splits the serial bit-stream B into two bit-

substreams of the same length. From a generalization point of view, using OOK to map the first bit-substream can be

considered as a special case of using two different constellation sizes (i.e. high-order QAM and low-order QAM) for

modulation. In this generic case, the original bit-stream is divided into three portions: a first bit-substream, a second bit-

substream, and a third bit-substream as in Fig.5

Then, the subcarrier-index modulator encodes the first bit-substream by associating each indexed subcarrier with

the index of each bit in the first bit-substream. Afterwards, two subsets of bit-values (ones and zeros) are identified with

the first bit-substream. The next step is to select two different modulation alphabets MH andML (i.e. 4-QAM and BPSK)

to be assigned to the first and the second subsets of the first bit-substream. For spectrally-efficient implementation, the

majority subset of the first bit-substream is allocated the high-order modulation while the minority subset is allocated the

low-order modulation (e.g. BPSK). Finally, the second bit-substream is mapped by modulating the subcarriers belonging to

the majority subset according to the constellation size ofMH, and the third bit-substream is mapped by modulating the

subcarriers belonging to the minority subset according to the constellation size ofML. Fig. illustrates an example on SIM

using two different modulation instead of OOK modulation.


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CHALLENGES AND REMEDIES OF VLC

Increasing Data Rate

Perhaps the simplest way of mitigating the low bandwidthof the transmitter is to block the phosphor component at

thereceiver by using a blue filterIt is also possible to improve the response by transmitterand/or receiver equalization, or

the use of bandwidth-efficientmodulation schemes that take advantage of the high availablesignal to noise ratio. In

addition, for higher data rates it maybe possible to use parallel data transmission from a number ofLEDs. Methods used to

meet the challenge:

Transmitter Equalization

Analogue equalization techniques can be used tocompensate for the rapid fall-off in response of the whiteLEDs at

high frequencies. It is possible to use an array of LEDs, each driven using a resonant technique with aparticular peak

output frequency to achieve this. Carefulchoice of a number of different frequencies allows the overallresponse to be

tuned to that desired.16 LED arrayis modified to have a bandwidth of 25MHz offering a data-rate of 40Mb/s for Non-

Return to Zero (NRZ) On-Off Keying (OOK). More complexequalization can also be used for single devices, and data

rates of 80Mb/s (NRZ OOK) have been demonstrated.

Receiver Equalization

Transmitter equalization has the disadvantage that thedrive circuits for the LED (which often involve currents

ofseveral hundred milliamps) need modification, and in atypical coverage area there may be a number of sources, making

the modifications potentially costly. In addition someof the signal energy used is not converted into light, thus reducing the

energy efficiency of the emitter.Equalisation at the receiver allows complexity to be at the receiver only.

Complex Modulation

A high-SNR, low-bandwidth channel is typically suited tohigh bandwidth efficiency multilevel modulation

schemes.Work in shows that 100Mbit/s is possible using DiscreteMulti-Tone Modulation (DMT). At present there is little

workin this area, and further studies are required in order to assessthe relative benefits of analogue equalization with

relativelysimple modulation, or complex modulation and limited channel bandwidth.

Parallel Communication (Optical MIMO)

In most illumination applications many LEDs are used toprovide the necessary lighting intensity. This offers

theopportunity of transmitting different data on each device oron different groups of emitters. For this to be successful

adetector array is required at the receiver, and this creates aMulti-Input Multi-Output (MIMO) system. Radio-frequency


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MIMO techniques can be applied to such optical transmissionsystems to relax the necessary alignment between the array

ofdetectors and array of sources. Work in shows that sucha system can allow multi-channel data communication, without

the need to align a particular detector with a corresponding source.

Provision of an Uplink

VLC using illumination sources is naturally suited tobroadcast applications, and providing an uplink to

thedistributed transmitter structures can be problematic. Several approaches have been investigated. In an infra-red uplink

is used to a transmitter co-located with the VLC source, and in a retro-reflecting transceiver is proposed. In this case the

retro reflector returns a proportion of theincident light to the transmitter, and this returned beam ismodulated to provide a

data path from the terminal to theinfrastructure. This is potentially very attractive, although thedata-rates that can be

achieved using available modulators arelow. Co-operation between VLC and RF wireless standardswould also allow full

connectivity for a terminal. A VLCdownlink can be combined with an RF uplink, and this canalso reduce the load on

shared RF channel, including overall network performance.

Regulatory Challenges

In most cases VLC is subject to regulation by a non-communications standard. This can be an eye-safety standard,

illumination regulation, or an automotive standard in the caseof traffic signals or signal lights. A VLC standard must

therefore encompass both communications and associated illumination practices. This is distinct from most

othercommunication standards, and presents the challenge ofcoordination across regulatory bodies and

frameworks.Currently there are activities in several areas. Within JapanVLCC has developed several national standards,

andthe IEEE 802.15c Study Group on VLC is currently working on producing the necessary documents to become

aworking group. Interest in these activities continues to grow, but perhaps the major challenge for the VLC community is

todevelop links with other relevant regulatory bodies to ensure compatibility of any techniques.

Features and Benefits1. Enormousamount of unregulated bandwidth2. No licensingrequirements,3. low-cost front end devices, and4. Nointerference with the operation of sensitive electronic systems.5. No electromagnetic interference (EMI) with radio systems, no e-smog6. Unregulated spectrum (optical frequencies) with worldwide availability7. Simple shielding by opaque surfaces (improved privacy)8. Omnipresence of LEDs in displays, signalling and illumination9. LEDs, as semiconductor components offer a significant potential for high-speed modulation10. Data transfer piggybacked on illumination (or signalling) to create broadcasting hot-spots11. Add-ons without additional infrastructural components12. Applications that do personal area communicationAPPLICATIONS

Applications for the technology can cover a wide range of vertical markets:

Domestic: e.g. Home automation, Internet access.For indoor environments, the LED will provide high performance

mobile data access, an area where RF providers have struggled to penetrate and a primary medium where mobile


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consumers access the Internet. In addition to providing lighting and data access, LED based lighting systems offer

considerable advantages in energy savings and controllability as well as opportunities for advanced home/building

management and connection to smart grid applications.

Transport: Communications via street lighting, traffic lights, aircraft passenger lighting, aircraft navigation lights with

identification transmission, car head/tail lamp communications.

Hospitals: Equipment and staff communications with no RFI problems.

Industrial: Industrial and office lighting with inbuilt communications and localisation, intrinsically safe communications -

- e.g. in areas with flammable materials.

Public sector: providing local information -- e.g. localised information transmission in museums, communications for civil

contingencies.

Homeland Security and Defence:Light does not penetrate walls like radio signals does, and thus it is a more secure

means of data transfer additional secure communication means, ad-hoc communication.

Underwater Visible Light Communication: Radio waves do not propagate for a long distance under water. We were

able to demonstrate that the flashlight visible light transmitter was able to transmit signals for 30 meter distance. A diver

can communicate with a buddy diver using voice. LED flashlights light is intensity-modulated. A photo diode is attached

next to LEDs. Rise is planning to sell the product in 2011.

CONCLUSIONS

VLC appears to be an important potential component in expanding useable bandwidth, protecting sensitive

electrical equipment and data, creating more biologically friendly communications technology, and helping develop

seamless computing applications.

Properly developed VLC could also be used, in conjunction with other measures, to help create more equipment-

friendly and biologically-friendly electromagnetic environments helping to create truly sustainable communications

technology.

REFERENCES

1. R. Abu-alhiga and H. Haas, Subcarrier-Index Modulation OFDM, in Proc. of the International Symposium onPersonal, Indoor and Mobile Radio Communications (PIMRC), Tokyo, Japan, Sep. 1316, 2009.

2. http://www.era.lib.ed.ac.uk/bitstream/1842/4632/1/Abu-Alhiga2010.pdf3. http://www.transeem.org/Upload/files/TEEM/10%20JEEMT10-027(238-241).pdf(project)4. http://www.cn.kagawa-nct.ac.jp/~arai/PDFs/Proceedings/C_8.pdf(p2)5. http://www.see.ed.ac.uk/research/IDCOM/d-light6. http://soe.northumbria.ac.uk/ocr/7. Novel Feedback and Signalling Mechanismsfor Interference Management and Efficient Modulation8. Visible Light Communications: challenges and Possibilities Dominic C. O'Brien, Lubin Zeng1, Hoa Le-Minh,

Grahame Faulkner, Joachim W. Walewski, Sebastian Randel,University of Oxford (UK); Siemens AG, Corporate

Technology, Information and Communications, Munich (Germany)

9. Visible Light Communications Consortium,www.vlcc.net, 2008

Documents

DATA TRANSMISSION THROUGH VISIBLE LIGHT