指導老師 : 王瑞騰 老師 學 生 : 李裕銘

1. Improved Channel Estimation Based on Parametric Channel Approximation Modeling for OFDM SystemsIEEE TRANSATIONS ON BROADCASTING , VOL. 54 NO. 2 JUNE 2008 指導老師 : 王瑞騰 老師學 生 : 李裕銘

2. OUTLINE • Introduction • System model • Fraction Taps Channel Approximation Estimations (FTCA) • Simulations and analyses • Conclusions • Rererence

3. INTRODUCTION • In this paper, improved channel estimation methods based on the parametric channel approximation model using pilot tones are proposed for the OFDM system . • The full-rank MMSE estimator has large computational complexity , and in parametric channel estimator can only be adopted in sparse multi-path fading channels. In order to solve these problems lying in with the channel models , a parametric model is proposed . This model is called “fraction taps channel approximation(FTCA)” channel model .

4. Channel Model • Channel impulse response of the multi-path fading channel the complex gain of the i-th propagation path the delay of the i-th propagation path • Frequency response

5. Orthogonal frequency division multiplexing(OFDM) system model Discrete-time baseband equivalent model of OFDM system

6. OFDM channel frequency response , k=0, 1, … , N-1 N : number of the subcarriers k : subcarrier index T : sampling interval hi : the complex gain of the i-th propagation • The observed channel

7. Time domain signal , n = 0 , 1, … , N-1 Ng : the number of samples in the guard interval which satisfies Ng x T≧ τmax

8. The received baseband signal , n = 0 , 1 , … , N-1 : additive white Gaussian noise (AWGN) : circular convolution , k = 0 ,1, … ,N-1

9. Fraction Taps Channel Approximation (FTCA) Estimations • The FTCA channel model : fraction factor selected from (0,1] : complex gain of the l-th approximation M : number of approximation taps

10. In matrix notation , the channel frequency response vector and then , , k=0~N-1 and l=1~M , k=0~N-1 and i=1~L

11. Based on the Least Square(LS) criterion g = (FHF)-1FHH = (FHF)-1FHWNh He : commonly very small and can be negligible when Ka is properly selected .

12. The pilot subcarriers arrangement

13. In OFDM system , the S pilot subcarriers are assumed to be evenly inserted into the N transmission subcarriers • Let P denote the set that contains the position indexes of the S pilot tones

14. The FTCA Estimators where , m=0,…,S-1 and l=1,…,M

15. The FTCA-MMSE Estimator(Minimu mean-square error) where

16. The Average Channel Energy Approximation Error (ACEAE) Be • For the channel frequency response is achieve by

17. The FTCA-LS Estimator For the channel frequency response is achieve by

18. Flowchart M

19. Simulations and analyses In the OFDM system Multi-path slow fading channel Carrier frequency : 1GHz Signal bandwidth (BS) : 2.5MHz Number of subcarriers (N) : 1024 Number of samples in the guard interval (Ng) : 32 Sampling interval (T) : 0.4 us

20. Τmax=0.64us

21. Τmax=0.64us , L=10

22. Τmax=0.64us , L=10 , Ka=0.72

23. Τmax,A=1.6us , Τmax,E=6.4us , L=10 , Ka,E=0.72 , Ka,A=0.51

24. Conclusions • As compared to the observed channel model , its dimension reduced, where the full-rank estimators using pilots tones can be adopted, and consequently, improves the channel estimation performance . • It eliminates the problem of multi-path delay estimation and can be adopted in a channel not restricted to a sparse mlti-path fading.

25. REFERENCES • J.-J. van de Beek , O. Edfors , and M. Sandell , “On channel estimation in OFDM systems,” in Proc. IEEE Vehicular Technology Conf. , Jul. 1995 , vol. 2 , pp. 815-819 • B. Yang , K. B. Letaief , R. S. Cheng , and Z. Cao , “Channel estimation for OFDM transmission in multipath fading channeds based on parametric channel modeling,” IEEE Trans. Commun. , vol. 49 , pp.467-479 , Mar. 2001.