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Chang Gung University 13/07/20061 Channel Analysis and Estimation for OFDM Systems with Doppler Effect Advisor : Yung-An Kao Student : Chien-Hsin Hsu

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Chang Gung University 13/07/20062 Outline Introduction Channel Analysis and Simulation Channel Estimation and Simulation Conclusion

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Chang Gung University 13/07/20063 Introduction (1/2) I propose the time-variant channel analysis which focuses on the same subcarrier in the different OFDM symbols. Time-variant channel analysis. a pilot-based estimation scheme (2-D linear interpolation).

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Chang Gung University 13/07/20064 Introduction (2/2) Mathematics model of Jakes’ Fading Channel and Line- of-Sight (LOS) component of the received signal. 7-path channel model, which includes the LOS. Specification of the 7-path channel model according to COST 207.

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Chang Gung University 13/07/20065 Channel Analysis (1/2) Fig. 1. The block diagram of an OFDM system. Do not consider “CFO”, “SFO” and “noise”. k : k-th subcarrier l : l-th OFDM symbol

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Chang Gung University 13/07/20066 Channel Analysis (2/2) HF k (e j ω ) is obtained by an ensemble average of 100 independent simulation runs. HF 6 (e j ω ). DFT l : time index (N : N points FFT)

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Chang Gung University 13/07/20067 Simulation Environment For DVB-T : Transmission mode : 2K Mode V=120km/hr. Modulation level chooses QPSK. f c =862MHz. Number of input OFDM symbol is 2 frame and there are 68 OFDM symbols in one frame. T s =7/64μs and 7/48μs are selected. GI=1/32 and 1/4.

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Chang Gung University 13/07/20068 Simulation Results Fig. 2. HF 6 (e jω ) versus normalized frequency for DVB-T (GI=1/32, T s =7/64μs). Fig. 3. HF 6 (e jω ) versus normalized frequency for DVB-T (GI=1/4, T s =7/48μs). HF 6 (e jω )

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Chang Gung University 13/07/20069 Channel Estimation (1/4) Channel estimation can be achieved by inserting pilots. 1-D linear interpolation is widely used in the industry (Channel frequency response and pilot). 2-D linear interpolation is proposed to solve the problem. Down-sampling and aliasing. Fig. 4.

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Chang Gung University 13/07/200610 Channel Estimation (2/4) Fig. 4. The pilot arrangement for DVB-T. symbol 66 symbol 1 symbol 2 symbol 0 symbol 3 symbol 67 k = 0 k = 1704 if 2K Mode k = 6816 if 8K Mode pilot data

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Chang Gung University 13/07/200611 Channel Estimation (3/4) Fig. 5. The diagram of 2-D linear interpolation. H 1,4 symbol 1 symbol 2 symbol 3 symbol 4 symbol 5 symbol 6 symbol 7 k = 1 k = 2 k = 3 k = 4 H 1,1 H 1,5 H 4,6 H 4,2 H 4,4 H 2,4 Step 1. The interpolation at the same subcarrier in the different OFDM symbols. Step 2. The interpolation at the different subcarriers in the same OFDM symbol.

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Chang Gung University 13/07/200612 Channel Estimation (4/4) The error (interpolated channel and H k [l]) is considered as noise. noise average power, or say, mean square error (MSE). Noise average power is obtained by an ensemble average of 100 independent simulation runs. “total” noise average power.

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Chang Gung University 13/07/200613 Simulation Environment For DVB-T : Transmission mode : 2K Mode V=20km/hr, 40km/hr, 60km/hr~120km/hr Modulation level chooses QPSK. f c =862MHz. Number of input OFDM symbol is 2 frame and there are 68 OFDM symbols in one frame. T s =7/64μs, 8/64μs and 7/48μs. GI=1/32 and 1/4.

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Chang Gung University 13/07/200614 Simulation Results Fig. 6. Total noise average power versus V for DVB-T (GI=1/4, T s =7/64μs, 8/64μs, 7/48μs). Fig. 7. Total noise average power versus V for DVB-T (GI=1/32, T s =7/64μs, 8/64μs, 7/48μs).

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Chang Gung University 13/07/200615 Conclusion It is clear the bandwidth of HF k (e jω ) increase with increasing the velocity. The performance of 2-D linear interpolation can be evaluated from the bandwidth of HF k (e j ω ). We can decide the largest interval of pilot at the same subcarrier in the different OFDM symbols from the bandwidth of HF k (e j ω ).

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Chang Gung University 13/07/200616 References [1] Chengshan Xiao, Yahong R. Zheng, and Norman C. Beaulieu, Fellow, IEEE “Second-order Statistical Properties of WSS Jakes’ Fading Channel Simulator,” IEEE Transactions on Communications, vol. 50, No. 6, June 2002. [2] Matthias Patzold, Mobile Fading Channels, John Wiley & Sons Ltd, 2002. [6] ETSI, “Digital video broad-casting (DVB); Framing structure, channel- coding and modulation for digital terrestrial television,” EN 300 744, v1.4.1,Jan. 2001. [3] Alan V. Oppenheim, Ronald W. Schafer with John R. Buck, Discrete-Time Signal Processing, Prentice Hall International, Inc., 2 nd ed, 1999. [4] Alan V. Oppenheim, Alan S. Willsky, with S. Hamid Nawab, Signals & Systems, Prentice Hall, 2 nd ed, 1996. [5] Theodore S, Rappaport, Wireless Communications-Principles and Practice, Prentice Hall PTR, 2 nd ed, 1996.

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Chang Gung University 13/07/200617 ~~~~ thanks for your attention ~~~~

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