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

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

3. 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).

4. 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.

5. 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

6. 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)

7. 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.

8. 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 )

9. 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.

10. 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

11. 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.

12. 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.

13. 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.

14. 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).

15. 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 ).

16. 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.

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