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1 Implementation and Performance Evaluation of an OFDM Modem With Variations in Cyclic Prefix Length and Channel Coding for Different Channels Indira Rajagopal.

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Presentation on theme: "1 Implementation and Performance Evaluation of an OFDM Modem With Variations in Cyclic Prefix Length and Channel Coding for Different Channels Indira Rajagopal."— Presentation transcript:

1 1 Implementation and Performance Evaluation of an OFDM Modem With Variations in Cyclic Prefix Length and Channel Coding for Different Channels Indira Rajagopal Joydeep Acharya Madhavi V Ratnagiri Sumathi Gopal Course: Communication Theory (ECE 545); Rutgers University Professor: Dr. Predrag Spasojevic

2 04/23/2003 OFDM Performance 2 Topics  Introduction to OFDM  Description of OFDM system simulated  Channel Simulation  Results  Conclusions  References

3 04/23/2003 OFDM Performance 3 Introduction to OFDM  Orthogonal Frequency Division Multiplexing;  Part of xDSL, IEEE a standards  Improves Data rates, such as 56Mbps in IEEE a

4 04/23/2003 OFDM Performance 4 Introduction to OFDM  Resilience to frequency selective channels Courtesy : “Multicarrier Primer”

5 04/23/2003 OFDM Performance 5 OFDM Transmitter Channel Coding Inter Leaving S/P Modulation (M) IFFT S/P Cyclic Prefix Mapping from size N/2 to N Source Data To Channel Bits per OFDM symbol = (IFFT_Size/2) * log 2 (M)

6 04/23/2003 OFDM Performance 6 Channel Coding Channel Coding Inter Leaving S/P Modulation IFFT P/S Cyclic Prefix Mapping from size N/2 to N Source Data To Channel BCH Code n = 31; k=16; t = 3; Convolutional code; Rate = ½ ; K=7 Courtesy: a std.

7 04/23/2003 OFDM Performance 7 Interleaving b1 b2 b3 b5 b4 b8 b9 b10 b6 b7 b12 b11 Read out Fill in Channel Coding Inter Leaving S/P Modulation IFFT P/S Cyclic Prefix Mapping from size N/2 to N Source Data To Channel

8 04/23/2003 OFDM Performance 8 Interleaving b1 b2 b3 b5 b4 b8 b9 b10 b6 b7 b12 b11 Read out Fill in b1b4b7b2b10b5b11b8b9b3b6b12 Channel Coding Inter Leaving S/P Modulation IFFT P/S Cyclic Prefix Mapping from size N/2 to N Source Data To Channel

9 04/23/2003 OFDM Performance 9 Modulation Schemes Used  QPSK (4-QAM)  16-QAM  64-QAM Channel Coding Inter Leaving S/P Modulation IFFT P/S Cyclic Prefix Mapping from size N/2 to N Source Data To Channel

10 04/23/2003 OFDM Performance 10 N/2 to N Mapper and IFFT IFFT Block Real Valued samples N N/2 Mapper Re(X N/2 ) X1X1 X N/2-1 Im(X N/ 2 ) X * N/2-1 N X*1X*1 X1X1 X2X2 X N/2-1 X N/2 Channel Coding Inter Leaving S/P Modulation IFFT P/S Cyclic Prefix Source Data To Channel Mapping from size N/2 to N X* n-k = X k where k : 1,… n/2

11 04/23/2003 OFDM Performance 11 Adding cyclic prefix Channel Coding Inter Leaving S/P Modulation IFFT P/S Cyclic Prefix Source Data To Channel Mapping from size N/2 to N Cyclic prefix length Time Original N Samples Added Prefix x(n) * h(n) = X(k)H(k)

12 04/23/2003 OFDM Performance 12 Channel Models  AWGN: r = s + n  Rayleigh Flat fading: r = ρs + n where ρ is Rayleigh distributed  Rayleigh Frequency Selective: r = h*s + n where h is channel impulse response r = h*s + n where h is channel impulse response

13 04/23/2003 OFDM Performance 13 OFDM Receiver Channel De- Coding De- Inter Leaving Demod FFT P/S Remove Cyclic Prefix Mapping from size N to N/2 From Channel Received Bits Thres- holding S/P

14 04/23/2003 OFDM Performance 14 Thresholding Channel De- Coding De- Inter Leaving Demod FFT P/S Remove Cyclic Prefix Mapping from size N to N/2 From Channel Received Bits Thres- holding S/P

15 04/23/2003 OFDM Performance 15 Thresholding based on decision regions for 16-QAM

16 04/23/2003 OFDM Performance 16 De-Interleaving b1b2b3 Fill in Read out b1b2b3 Channel De- Coding De- Inter Leaving Demod FFT P/S Remove Cyclic Prefix Mapping from size N to N/2 From Channel Received Bits Thres- holding S/P b4b5b6 b7b8b9 b10b11b12 b4b5b6b7b8b9b10b11b12

17 04/23/2003 OFDM Performance 17 Topics  Introduction to OFDM  Description of OFDM system  Channel Models  Results  Conclusions  References

18 04/23/2003 OFDM Performance 18 Received Signal Constellation for 16-QAM in Presence of AWGN

19 04/23/2003 OFDM Performance 19 Bit Error Rate for AWGN for various IFFT sizes

20 04/23/2003 OFDM Performance 20 Bit Error Rate for AWGN for various Modulation Schemes

21 04/23/2003 OFDM Performance 21 Bit Error Rate for AWGN with and without Coding

22 04/23/2003 OFDM Performance 22 OFDM spectrum

23 04/23/2003 OFDM Performance 23 Coded and uncoded BER for flat fading Rayleigh channel

24 04/23/2003 OFDM Performance 24 Effect of varying cyclic prefix in a flat fading channel

25 04/23/2003 OFDM Performance 25 Conclusions We were able to demonstrate the performance of an OFDM system in AWGN channel and a Rayleigh channel with flat fading We were able to demonstrate the performance of an OFDM system in AWGN channel and a Rayleigh channel with flat fading

26 04/23/2003 OFDM Performance 26 Further work  Obtain BER plots of frequency selective channel with and without coding  Demonstrate change in BER with change in length of cyclic prefix, for a frequency selective channel  Analyze any tradeoffs between coding and length of cyclic prefix

27 04/23/2003 OFDM Performance 27 References  IEEE a standard  J. M. Cioffi, “A multicarrier primer,” ANSI T1E1.4 Committee Contribution, Nov   Rappaport, T.S., “Wireless Communications, Principles and Practice”, Second Edition Prentice Hall.   Sklar Bernard, “Digital Communications”, Pearson Education Asia, Second Edition, 2001.

28 04/23/2003 OFDM Performance 28 Acknowledgements  WINLAB students and faculty: Predrag, Leo, Praveen, Hithesh, Ahmed, Lang, Rueheng, Jassi, Amith, and many more.  Zoran Kostic at Thomson Inc. It was FUN! Thank You for your patience


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