1. Improved Channel Estimation Based on Parametric Channel Approximation Modeling for OFDM Systems IEEE 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 , vol. 2 , pp
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 , Mar