IMPROVEMENT OF BER IN LED BASED INDOOR COMMUNICATION

1. IMPROVEMENT OF BER IN LED
BASED INDOOR COMMUNICATION
USING OPP MODULATION AND
LDPC CODING
1

2. INTRODUCTION
INDOOR OPTICALWIRELESS SYSTEM
LDPC ENCODING
MODULATIONTECHNIQUES
LDPC DECODING
BIT ERROR RATE STUDY
APPLICATION
CONCLUSION
2

3. 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.
3

4. Property 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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6.  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.

7. 7
 VLC is used for
 Vehicle to vehicle communication
 Networking in indoor environments
VISIBLE LIGHT COMMUNICATION(VLC)

8. 8
An illustration of the VLC concept

9. INDOOR OPTICAL SYSTEM
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10. MODELS

11. WORKING TECHNOLOGY
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12. DATA
OPPM
MODULATION
LDPC
ENCODING
INDOOR
CHANNEL
LDPC
DECODING
PHOTODIODEOPPM
DEMODULATION
BER
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

14. 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

15. 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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16. 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
16

17. Overlapping pulse position modulation
Type of pulse position modulation with overlapping.
Message of duration Tsym divided into symbols
Each 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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18. INDOOR
CHANNEL
LDPC
DECODING
PHOTODIODEOPPM
DEMODULATION
ORIGINAL
DATA
18
RECEIVER SIDE
BER
CALCULATION

19. 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.

21. LDPC DECODING
 Bit-Flipping Algorithm
 Bits are continually flipped .
 Step 1: For each received variable nodes vi , calculate the
check node cj . Terminate the algorithm if all cj =0
 Step 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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22. 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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23. 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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24. Flip vk associated with
c1=[v0v1v2v5] since c1=1
SinceSince c2=0 convert the
associated nodes of c2 back
to original mode.
vk=[v2,v5,v6,v7] =[0101]
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25. 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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26. 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
26

27. BIT ERROR RATE STUDY
OOK MODULATION
OPPM MODULATION
WITH LDPC CODING27

28. Can provide network access at
 Home
 Office
 Shopping Center
 Mining Areas
 Vehicle traffic communication
APPLICATIONS
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29. CONCLUSION
Cost 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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30. 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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