1. A Soft Decision Decoding Scheme for Wireless COFDM with Application to DVB-T Advisor : Yung-An Kao Student : Chi-Ting Wu 2005.03.01

2. Yong Wang, JianHua Ge, Bo Ai, Pei Liu, ShiYong Yang, “ A Soft Decision Decoding Scheme for Wireless COFDM with Application to DVB-T, ” Consumer Electronics, IEEE Transactions on, Volume: 50, Issue: 1, Feb 2004 Pages:84 - 88

3. Outline Introduction Soft decision decoding in DVB-T system Proposed CSI estimation method CCI detecting and erasing technique Simulation results Conclusion

4. Introduction Basic idea of OFDM is to split the data onto subcarriers to combat multipath channel Fading magnitude differs from subcarrier In DVB-T system, co-channel interference (CCI) causes signal distortion Analog signals

5. Soft decision decoding in DVB-T system (Tx) Convolution code RS code QPSK 16QAM 64QAM 1/32, 1/16, 1/8, 1/4 2k or 8k mode DVB-T signals will be transmitted in VHF/UHF channels with frequency spacing of 6~8 MHz VHF:30~300 MHz UHF:300~3000 MHz

6. Soft decision decoding in DVB-T system (Rx) CSI is often defined as Carrier-to-Noise Ratio (CNR) CCI can also be referred to as frequency selective interference The reliability could be treated as a priori information

7. Proposed CSI estimation method (1/4) Several methods of CSI generation Square of the channel frequency response it doesn ’ t take account of the effect of noise power Interpolating the MSE of the pilot subcarriers it assumes that the channel is varying slowly enough, not suitable for mobile channel Properly defined metric distance between the received data and hard decision constellation

8. Proposed CSI estimation method (2/4) if l : symbol index k : subcarrier index N : Gaussian noise with power Y : FFT output signal X : transmitted signal H : channel frequency response

9. Proposed CSI estimation method (3/4) In general, CNR for k-th subcarrier can be defined as compare to both equations where denotes time-averaging function over the OFDM symbol and

10. Proposed CSI estimation method (4/4) In fast time-varying channel, we should take account of the factor of Doppler shift. Channel correlation estimator is to detect the correlation of the H k,l in time direction and corresponding iterative factor The shorter the minimum coherence time, the greater the iterative factor should be. Therefore, we could obtain the data reliability metric Bit decision metric m k,l (i is equal to 2,4,6 for QPSK, 16QAM, 64QAM)

11. CCI detecting and erasing technique There ’ s no extra spectrum for DVB-T, so analog and digital signals have to co-exist Utilize the property of CCI to detect the distorted subcarrier positions and erased them We can detect according to the amplitude deviation of the estimated H k,l in time direction

12. Simulation results 2k mode DVB-T system ½ inner code rate 1/16 guard interval symbol interleaver only 4-bit quantization Trace back length = 80 Rayleigh fading channel 64 QAM BER comparison of CSI generation method under Rayleigh fading channel

13. Simulation results 2k mode DVB-T system ½ inner code rate 1/16 guard interval symbol interleaver only 4-bit quantization Trace back length = 80 Rayleigh fading channel QPSK Doppler shift = 100Hz BER comparison of different iterative factor under Rayleigh fading channel with f Dmax =100 Hz

14. Simulation results 2k mode DVB-T system ½ inner code rate 1/16 guard interval symbol interleaver only 4-bit quantization Trace back length = 80 Rayleigh fading channel 64 QAM Interference = 60/1705 = 3.51% CNR of signal = 40dB BER comparison of soft-decision decoder with and without CCI erasing under Rayleigh fading channel with PAL interference

15. Conclusion The size of soft-decision metric caries adaptively in accordance with CSI and CCI By selecting suitable iterative factor, the CSI could be used for mobile reception This method has been used in BDB-T(Terrestrial Broad-band Digital Broadcasting) and HDTV in China