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International Journal of Electronics, Communication & Instrumentation Engineering Research and Development (IJECIERD) ISSN 2249-684X Vol. 2 Issue 4 Dec 2012 81-88 Š TJPRC Pvt. Ltd.,

DATA TRANSMISSION THROUGH VISIBLE LIGHT 1 1 2

RASTE MADHURA M, 2GHADIGAONKAR AMIT H & 2THARA RAFAT A

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

B.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. That’s 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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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

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

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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Data Transmission through Visible Light

SCIPPM

Sub-Carrier PPM Figure 4

b)

Frequency {shift keying}: In frequency shift keying (FSK) data is represented by varying frequencies of the

carrier 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 bitsubstreams 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 bitsubstream, 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 and ML (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 of MH, and the third bit-substream is mapped by modulating the subcarriers belonging to the minority subset according to the constellation size of ML. Fig. illustrates an example on SIM using two different modulation instead of OOK modulation.


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

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 NonReturn 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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Data Transmission through Visible Light

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 Benefits 1.

Enormousamount of unregulated bandwidth

2.

No licensingrequirements,

3.

low-cost front end devices, and

4.

Nointerference with the operation of sensitive electronic systems.

5.

No electromagnetic interference (EMI) with radio systems, no e-smog

6.

Unregulated spectrum (optical frequencies) with worldwide availability

7.

Simple shielding by opaque surfaces (improved privacy)

8.

Omnipresence of LEDs in displays, signalling and illumination

9.

LEDs, as semiconductor components offer a significant potential for high-speed modulation

10. Data transfer piggybacked on illumination (or signalling) to create broadcasting hot-spots 11. Add-ons without additional infrastructural components 12. Applications that do personal area communication

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

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 flashlight’s 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 equipmentfriendly 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 on Personal, Indoor and Mobile Radio Communications (PIMRC), Tokyo, Japan, Sep. 13–16, 2009.

2.

http://www.era.lib.ed.ac.uk/bitstream/1842/4632/1/Abu-Alhiga2010.pdf

3.

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-light

6.

http://soe.northumbria.ac.uk/ocr/

7.

Novel Feedback and Signalling Mechanismsfor Interference Management and Efficient Modulation

8.

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

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