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研究生:李啟碩
研究生(外文):Chi-ShuoLi
論文名稱:OFDM系統使用引導信號之頻域與時域通道估測
論文名稱(外文):Frequency-Domain and Time-Domain Pilots-Aided Channel Estimation for OFDM Systems
指導教授:張名先
指導教授(外文):Ming-Xian Chang
學位類別:碩士
校院名稱:國立成功大學
系所名稱:電腦與通信工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2010
畢業學年度:98
語文別:英文
論文頁數:53
中文關鍵詞:正交分頻多工通道估測通道響應等化器
外文關鍵詞:OFDMchannel estimationchannel impulse responseequalizer
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在無線通訊中,接收端需要得到通道資訊來等化通道的效應,以減輕多路徑的干擾在頻域上使得訊號的失真。而在決定等化器參數時,需要得到通道的頻率響應,在此篇論文中,我們在正交分頻多工系統下之時域或頻域上放入一組接收器已知的引導訊號,來估測時域和頻域通道響應。 論文中將通道估測方法分為頻域和時域兩種方法。時域估測法在時域上將資料區塊之前傳送一個接收器已知振福的脈衝,接收端能藉此獲得完整的通道響應資訊以及多路徑的數量。頻域估測法在部分的子頻帶上放入已知訊號,在其他非已知訊號上的通道頻域資訊則再藉由最小平方法和線性最小均方誤差法…等方法來估得。之後再將時域和頻域通道估測方法拓展至二維,以一次估測多個時間的通道響應來達成更好且低複雜度的估測,以兩種不相同的架構來完成二維的估測及比較其好壞。最後也在當通道延遲不在取樣時間點上發生的情況上探討其效應,並且使用超取樣來補償產生的失真。
In wireless communications, receiver needs the information of the fading channel to equalize or mitigate the distortion of the received signal. We need frequency response of the channel (CFR) to determine coefficients of the equalizer. In this thesis we estimate the channel response of OFDM systems by inserting among data symbols some pilot signals that is known to the receiver. We consider both the pilot signals in time and frequency domains.
We use time-domain (TD) and frequency-domain (FD) estimations. For the TD estimation approach, we directly transmit one pulse whose amplitude is known to the receiver in time domain before every data block, and we can easily obtain the whole instant CIR and decide the path number at the receiver. For the FD estimation approaches, we insert pilots in some subcarriers (pilot subcarriers). The CFR at other sub-channels are obtained by linear interpolation. Then we propose a two-dimension method by allowing channel estimation processed after receiving several OFDM blocks, and estimate the channels jointly to obtain better performance. Finally, we study the effect of the channel delays that are not on sampling instant exactly, and use the oversampling to compensate the distortions.
Chinese Abstract...I
English abstract...II
Acknowledgement...IV
List of Tables ...VIII
List of Figures ...IX
Chapter 1. ...1
Introduction...1
1.1 Motivation ... 1
1.2 Organization of this thesis....2
Chapter 2. ...4
System and Channel Model ...4
2.1 Orthogonal Frequency Division Multiplexing (OFDM)...4
2.2 Channel Model ...6
2.2.1. Jake’s Rayleigh Fading Model ...6
2.2.2. Multipath Model...7
Chapter 3. ...9
One-Dimension Channel Estimation ...9
3.1 Frequency-Domain Approach for Channel Estimation...10
3.1.1. Linear Minimum Mean-Squares Error (LMMSE) ... 12
3.1.2. Least-Squares Fitting Approach (LSF) ...14
3.1.3. Least-Square Fitting – Channel Impulse Response (LSF-CIR)...16
3.1.4 Modified Least-Square Fitting – Channel Impulse Response(MLSF-CIR) ...19
3.2 Time-Domain Approach for Channel Estimation...20
3.2.1 Zero Forcing(ZF) ...22
3.2.2 TD Linear Minimum Mean-Squares Error (TD-LMMSE)...23
3.3 Simulation of One-Dimension Approaches... 25
3.3.1 Parameter Adjustment...25
3.3.2 Simulation result ...28
3.4 LSF-CIR Approach With Unknown Channel Length.... 30
3.4.1. Power Selection Method...31
Chapter 4. ...35
Two-Dimension Channel Estimation...35
4.1 2D Frequency-Domain Approach for Channel Estimation...36
4.1.1 2D Linear Minimum Mean Square Error (2D LMMSE)...37
4.1.2 2×1-D Linear Minimum Mean Square Error ( 2×1-D LMMSE)... 39
4.1.3 2×1-D Least-Square fitting – Channel Impulse Response +
Polynomial ( 2×1-D LSF – CIR + poly.) ...40
4.2 2D Time-Domain Approach for Channel Estimation ...42
4.3 Simulation result of two-dimension approaches...43
Chapter 5. ...46
The study of the influence on channel which is not on sampling
instant for LSF-CIR approach ...46
Chapter 6. ...51
Conclusion ...51
Bibliography...53
[1]Y. Li, and X. Huang, “The Simulation of Independent Rayleigh Faders, IEEE Trans. Commun., vol. 50, NO. 9, pp. 1503-1514, Sept. 2002.
[2]M. X. Chang and Y. T. Su, “2-D regression channel estimation for equalizing OFDM signals, Proc IEEE 51th Vehicular Technology Conference, Tokyo, pp. 240-244, May 2000.
[3]M. X. Chang and Y. T. Su, “Model-based channel estimation for equalizing OFDM signal, IEEE Trans. Commun., vol. 50, pp. 240-544, Apr. 2002.
[4]M. X. Chang and Y. T. Su, “Performance Analysis of Equalized OFDM System in Rayleigh Fading, IEEE Trans. Commun., vol. 1, NO. 4, October 2002.
[5]M. X. Chang, “A new derivation of of Least-Square-Fitting principle for OFDM channel estimation, IEEE Trans. Wireless Commun. , VOL. 5, NO. 4, APRIL 2006.
[6]P. Hoeher, S. Kaiser, and P. Robertson, “Two-Dimensional Pilot-Symbol- Aided Channel Estimation, ISIT 1997, Ulm. Germany, June 29 - July 4
[7]P Hoeher, “TCM on Frequency-Selective Land-Mobile Fading Channels, et al. – 1991
[8]K. C. Hung and D. W. Lin, “Pilot-Based LMMSE Channel Estimation for OFDM Systems With Power–Delay Profile Approximation, IEEE Veh. Technol. Mag., VOL. 59, NO. 1, JANUARY 2010
[9]D. Hu, L. He, and L. Yang, “Joint Pilot Tone and Channel Estimator Design for OFDM Systems, IEEE Commun. Letters, VOL. 10, NO. 10, OCTOBER 2006

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