IMPROVEMENT OF BER IN LED BASED INDOOR

COMMUNICATION USING OPP MODULATION AND LDPC

CODING

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OutlineINTRODUCTION

INDOOR OPTICAL WIRELESS SYSTEM

LDPC ENCODING

MODULATION TECHNIQUES

LDPC DECODING

BIT ERROR RATE STUDY

APPLICATION

CONCLUSION

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INTRODUCTION Wireless communication technology developing fast.

We require high data rate.

Visible light optical communication more attractive compared to conventional RF band.

Free space optical communication suffers challenges.

New modulation schemes are introduced.

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VLC vs. RF CharacteristicsProperty VLC RF

Bandwidth Unlimited, 400nm-700nm

Regulatory, BW Limited

EMI or RFI  No High

Harmless for human body

NO YES

Power Consumption

Relative low Medium

Coverage Distance

Security

Short

More secure

Medium

Not secure

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WHY ONLY VLC ???

Gamma rays ,X-rays ,Ultraviolet light dangerous for the human body.Infrared, due to eye safety regulation, can only be used with low power.

HENCE WE USE THE VISIBLE - LIGHT SPECTRUM.

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VLC is used for Vehicle to vehicle communication Networking in indoor environments

VISIBLE LIGHT COMMUNICATION(VLC)

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An illustration of the VLC concept

INDOOR OPTICAL SYSTEM

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GIGA SHOWER

GIGA MIMO

MODELS

WORKING TECHNOLOGY

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DATA OPPM

MODULATIONLDPC

ENCODING

INDOOR CHANNEL

LDPC DECODING

PHOTODIODEOPPM DEMODULATIONBER

CALCULATION

LED

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Required in communication system.

Extra parity bits are added to the message.

Receiver can retrieve original data that is corrupted.

Error control coding

Low Density Parity Check Codes

LDPC codes were developed by Robert Gallager.Class of linear block code. LDPC codes are decoded iteratively. Error correcting code.Perform close to Shannon theory.Characterised by a sparse parity check matrix which

contains only few ‘1’s in comparison to ‘0’s. LDPC codes are regular LDPC codes if H has

uniform number of 1’s in columns and rows.14

LDPC ENCODING

Given some sparse parity check matrix H.If unsystematic we can use row and column

operations to set H′ = [PT |In−k].Find the generator matrix G.Since G = [Ik |P] Codeword vector ,c = xG.

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MODULATION TECHNIQUES

Amplitude shift keying.Conventional technique used in optical communication.Generation of optical pulse by ON/OFF of LED.Data rate less.

OOK MODULATION

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Overlapping pulse position modulationType of pulse position modulation with overlapping.Message of duration Tsym divided into symbolsEach pulse covers N time slots.In normal case we can have Q alphabets.On overlapping we can transmit J symbols.J=N(Q-1)+1 symbols.Bandwidth and throughput efficient.High data rate.

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INDOOR CHANNEL

LDPC DECODING

PHOTODIODEOPPM DEMODULATIONORIGINAL

DATA

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RECEIVER SIDE

BER CALCULATION

Geometric approach to LDPC codes

Tanner Graph has two classes of nodes:

Variable nodes (v): correspond to bit/symbol nodes to

columns of H.For (n−k)×n matrix H, we have n v nodes.

Check nodes (c): correspond to parity check equations to the rows of H

We have (n−k )c nodes

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C0=V1,V3,V4,V7.C1=V0,V1,V2,V5.C2=V2,V5,V6,V7.C3=V0,V3,V4,V6.

LDPC DECODING

Bit-Flipping AlgorithmBits are continually flipped .Step 1: For each received variable nodes vi , calculate the

check node cj . Terminate the algorithm if all cj =0Step 2: For each check node cj , j = 1,2, . . . consecutively,

we flip the bits of the connected variables nodes {vk} in order if cj = 1 and converts back to received bits if cj = 0

Step 3: Go back to Step 1

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Assume that an error free received codeword is V=[10010101].Since VHT=[0000] this is a valid codeword.

For the matrix

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Received code word V=10010101 with no error.VHT=[0000]

If received codeword V=11010101 is with 1 error.VHT=[1100] .Flip vk associated with c0=[v1v3v4v7]

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Flip vk associated with c1=[v0v1v2v5] since c1=1

Since Since c2=0 convert the associated nodes of c2 back to original mode.vk=[v2,v5,v6,v7] =[0101]

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Since c3=0 convert the associated nodes of c3 back to original mode.vk=[v0,v3,v4,v6] =[1100]

Going back to step 1 we have c0,c1,c2,c3=0 and algorithm terminates.We got code word c=10010101 which is the original error free code word.

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Ratio of number of wrong bits to number of total bits.Probability of error is the theoretically predicted expected BER.The more the signal is affected, the more bits are incorrect.When photon count increases BER decreases.It is a major indicator of the health of the system.

BIT ERROR RATE

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BIT ERROR RATE STUDY

OOK MODULATION OPPM MODULATION WITH LDPC CODING 27

Can provide network access at Home Office Shopping Center Mining Areas Vehicle traffic communication

APPLICATIONS

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CONCLUSIONCost reduced. No interference on RF signals.High data rate with less error is achieved. Safe for health .Large amount of energy can be saved. Attractive alternative for mobile computers and communication.

If this technology put into practical use , every bulb act like hotspots to transmit wireless data.

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REFERENCES

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[1] E. Cho, J. H. Choi, C. Park, M. Kang, M. Shin, Z. Ghassem looy, and C.G. Lee, “NRZ-OOK signaling with LED dimming for visible light communication link,” in Proc. NOC, pp. 32–35,IEEE-2011.[2] J. Grubor, S. Lee, K. Langer, T. Koonen, and J. Walewski, “Wireless High-Speed Data Transmission with Phosphorescent White-Light LEDs,” in Eur. Conf. Optical Communication, Berlin, Germany, 2007.[3] J. Vucic, C. Kottke , S. Nerreter , A. Buttner, K. D. Langer, and J.W.Walewski, “White light wireless transmission at 200+ Mb/s net data rate by use of discrete-multitone modulation,” IEEE Photon. Technol.Lett. 21, 1511–1513 ,2009.[4] S. Iwasaki, C. Premachandra, T. Endo, T. Fujii, M. Tnimoto, Y.Kimura, “Visible Light Road-to-Vehicle Communication Using High-Speed Camera,” Proc. IEEE Intelligent Vehicle Symposium, pp. 13-18,2008[5] H. M. H. Shalaby, “Capacity and cutoff rate for optical overlapping pulse-position modulation channels,” IEEE Trans. Commun. 43, 1284–1288 ,1995.

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