IMPROVEMENT OF BER IN LED BASED INDOOR COMMUNICATION

696 views

Published on

IMPROVEMENT OF BER IN LED BASED INDOOR COMMUNICATION

Published in: Engineering, Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
696
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
25
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

IMPROVEMENT OF BER IN LED BASED INDOOR COMMUNICATION

  1. 1. IMPROVEMENT OF BER IN LED BASED INDOOR COMMUNICATION USING OPP MODULATION AND LDPC CODING 1
  2. 2. INTRODUCTION INDOOR OPTICALWIRELESS SYSTEM LDPC ENCODING MODULATIONTECHNIQUES LDPC DECODING BIT ERROR RATE STUDY APPLICATION CONCLUSION 2
  3. 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. 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
  5. 5. 5
  6. 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. 7  VLC is used for  Vehicle to vehicle communication  Networking in indoor environments VISIBLE LIGHT COMMUNICATION(VLC)
  8. 8. 8 An illustration of the VLC concept
  9. 9. INDOOR OPTICAL SYSTEM 9
  10. 10. MODELS
  11. 11. WORKING TECHNOLOGY 11
  12. 12. DATA OPPM MODULATION LDPC ENCODING INDOOR CHANNEL LDPC DECODING PHOTODIODEOPPM DEMODULATION BER CALCULATION LED 12
  13. 13. 13 Required in communication system.  Extra parity bits are added to the message. Receiver can retrieve original data that is corrupted. Error control coding
  14. 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. 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. 15
  16. 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. 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. 17
  18. 18. INDOOR CHANNEL LDPC DECODING PHOTODIODEOPPM DEMODULATION ORIGINAL DATA 18 RECEIVER SIDE BER CALCULATION
  19. 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 19
  20. 20. 20 C0=V1,V3,V4,V7. C1=V0,V1,V2,V5. C2=V2,V5,V6,V7. C3=V0,V3,V4,V6.
  21. 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 21
  22. 22. Assume that an error free received codeword is V=[10010101]. Since VHT=[0000] this is a valid codeword. For the matrix 22
  23. 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] 23
  24. 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] 24
  25. 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. 25
  26. 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. 27. BIT ERROR RATE STUDY OOK MODULATION OPPM MODULATION WITH LDPC CODING27
  28. 28. Can provide network access at  Home  Office  Shopping Center  Mining Areas  Vehicle traffic communication APPLICATIONS 28
  29. 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. 29
  30. 30. REFERENCES 30 [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.
  31. 31. 31

×