本論文主要探討多輸入多輸出之正交分頻多工(Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing, MIMO-OFDM)系統的通道估測。對多輸入多輸出系統的接收端而言，通道估測對系統效能有關鍵的影響。在本論文中，我們採用空頻區塊碼之正交分頻多工(Space-Frequency Block Codes - Orthogonal Frequency Division Multiplexing, SFBC-OFDM)的系統架構，同時採用疊加序列(Superimposed Training)的方法來提高頻寬使用效率。我們除了利用資料訊號的一階統計特性來降低未知訊號對疊加序列的干擾，更結合改良型最小平方(Modified Least Square, MLS)估測和決策回饋(Decision Feedback)來改善通道估測的準確度。在此，有別於傳統的決策回饋通道估測法的干擾消除，我們利用空頻區塊碼本身的特性進行決策回饋通道估測。我們更進一步在考慮解調錯誤的情況下，分析決策回饋對通道估測效能的影響。由分析結果得知，藉由空頻區塊碼本身特性進行決策回饋通道估測時並不會增加其運算複雜度，且其效能更優於常見的干擾消除方式。

In this thesis, channel estimation technique in Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems is investigated. Channel estimation plays an important role in the receiver performance of the MIMO-OFDM systems. In this thesis, the Space-Frequency Block Codes - Orthogonal Frequency Division Multiplexing (SFBC-OFDM) structure with the superimposed training scheme are adopted to increase bandwidth efficiency. In addition to using the first-order statistics of the received signal to reduce the interference induced by the unknown signals, the modified least square (MLS) estimator and the decision-feedback scheme are combined together to improve the channel estimation. In contrast to the conventional interference cancellation scheme for channel estimations adopting the decision feedback mechanism, the structure of the SFBC is utilized to decrease the interference. Furthermore, the effects of the decision-feedback scheme with erroneous decisions upon channel estimation are also examined. Analytical results show that the proposed method has better performance and computation complexity is not increased.

第一章　導論................................................................................................................1
1.0引言..........................................................................................................1
1.1研究動機..........................................................................................................2
1.2論文架構..........................................................................................................2
第二章 多輸入多輸出之正交分頻多工系統............................................................3
2.0引言.......................................................................................................3
2.1 正交分頻多工系統簡介..................................................................3
2.2利用離散傅立葉轉換的正交分頻多工系統..............................................5
2.3利用循環字首維持正交性的OFDM系統................................................7
2.4 BLAST架構與解調(空間分工).....................................................8
2.5 STBC架構(時間分集).....................................................10
2.6 SFBC架構(空間分集).....................................................12
第三章 傳統OFDM系統中通道估測方法之簡介........ .............................14
3.0引言................................................................................................................14
3.1同調偵測與差分偵測....................................................................................14
3.2常見內插法...................................................................................................17
3.3常用通道估測器............................................................................................19
第四章 多輸入多輸出系統之通道估測.................................................................21
4.0引言................................................................................................................21 4.1系統模型................................................................21
4.2改良型最小平方估測器與決策回饋...........................................................24
4.3 SFBC-OFDM之通道估測與解調..............................................26
4.4 SFBC-OFDM之傳統決策回饋..............................................29
4.5 SFBC-OFDM之空頻區塊碼決策回饋.....................................31
4.6複雜度比較......................................................................34
第五章 系統模擬與分析.........................................................................................36
5.0引言..........................................................................36
5.1改良型最小平方估測器與決策回饋........................................36
5.2空頻區塊編碼與決策回饋........................................38
第六章 結論..............................................................................................................45參考文獻.....................................................................................................................46

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