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Soft Decision Decoding with Channel State Information in OFDM systems

Soft Decision Decoding with Channel State Information in OFDM systems. Advisor : Yung-An Kao Student : Chi-Ting Wu 2004.10.06. Outline. Introduction C hannel S tate I nformation generation Viterbi decoder using CSI Some simulation result Conclusion. Frequency selective fading.

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Soft Decision Decoding with Channel State Information in OFDM systems

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  1. Soft Decision Decoding with Channel State Information in OFDM systems Advisor : Yung-An Kao Student : Chi-Ting Wu 2004.10.06 Wireless Communication Lab. CGU

  2. Outline • Introduction • Channel State Information generation • Viterbi decoder using CSI • Some simulation result • Conclusion Wireless Communication Lab. CGU

  3. Frequency selective fading Spectrum efficiency Introduction • Single carrier system ?? • Multi carrier system ?? • OFDM ! Wireless Communication Lab. CGU

  4. Channel State Information • Often defined as SNR in a carrier position • Different reliability depends on different subcarriers • Used as the input of soft decision decoder Wireless Communication Lab. CGU

  5. CSI generation ~ conv. • In conventional Channel estimation part of equalizer Signal power Signal power (SNR) Noise power Pilot carrier positions Noise power Wireless Communication Lab. CGU

  6. : the reference value of pilot at position carrier k : the channel response of k : noise component CSI generation ~ MSE(1/2) FFT output as follows Block diagram of OFDM receiver Wireless Communication Lab. CGU

  7. CSI generation ~ MSE(2/2) estimated equalized output of the kth pilot carrier position ~ where is the estimated value of the channel response The MSE of is estimated as follows If , equation above becomes ~ inverse SNR !! Wireless Communication Lab. CGU

  8. Viterbi decoder using CSI • In conventional, all branch metrics are calculated by the equal weighting • Here, we added the CSI into the BMC block as the different weighting of different subcarriers • Therefore Block diagram of Viterbi decoder Wireless Communication Lab. CGU

  9. Demapping reliability example 16-QAM constellation mappings and the corresponding bit patterns Metric of the certainty of each decision. 16-QAM, a) 1st or 2nd bit, b)3rd or 4th bit Wireless Communication Lab. CGU

  10. Simulations Wireless Communication Lab. CGU

  11. Simulations Wireless Communication Lab. CGU

  12. Conclusion • The CSI of each subcarriers will be obtained by using interpolation between the pilots • CSI is often defined as SNR • Use the MSE to obtained the inverse SNR • More quantization bit earns better performance Wireless Communication Lab. CGU

  13. Reference • [1]W.C. Lee, et al, “A Demapping Method Using the Pilots in COFDM System”, IEEE 1998 ICCE, pp.476-477, June 2-, LA, USA • [2]W.C. Lee, H.M. Park, et al,” Performance Analysis of Viterbi Decoder Using Channel State Information in COFDM System”, IEEE Trans. On Broadcasting, Vol.44, No.4, Dec. 1998 • [3]W.C. Lee, H.M. Park, et al,” Viterbi Decoding Method Using Channel State Information in COFDM System”, ICCE, IEEE Transactions on ,Vol. 45,Issue: 3 ,Aug. 1999 • [4]M. Rahnema, Y. Antia, et al,” Optimum Soft Decision Decoding with Channel State Information in the Presence of Fading”, IEEE Comm. Magazine July 1997 • [5]M.H. Hsieh, C.H. Wei,” Channel Estimation for OFDM Systems Based On Comb-Type Pilot Arrangement in Frequency Selective Fading Channels”, ICCE, IEEE Transactions on,Volume: 44 ,Issue: 1 ,Feb. 1998 • [6]Y. Wang, J.H. Ge, et al, “A Soft Decision Decoding Scheme for Wireless COFDM with Application to DVB-T”, ICCE, Transactions on, Vol. 50, No. 1, Feb. 2004 Wireless Communication Lab. CGU

  14. Thank you ~ Wireless Communication Lab. CGU

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