無線傳輸因受到符碼間干擾(ISI)而影響通訊品質。而為了達到所要求的系統效能，在接收端必須消除符碼間干擾所造成的影響，等化器的目的便是用來抑制符碼間干擾在傳輸上所造成的影響。另外，為了因應高速傳輸速率，正交分頻多工(OFDM)之多載波調變技術今日已經應用於許多通訊系統上，而多載波調變技術(MCM)可歸類為區塊傳輸。區塊傳輸系統中，可以在傳送端利用有限長濾波器組引入冗長資料量(redundancy)以達到消除區塊間干擾的目的。然而，冗長資料量的長度會影響系統效能，而冗長資料量長度的要求應通道的脈衝響應有極大的關連性。處理符碼間干擾的方法相繼提出，其中，利用非正交投影之FIR迫零(zero-forcing)等化器提供了一個可以將符碼間干擾和區塊間干擾分開作處理的架構。
在本論文中，我們提出一個新的等化方法：結合非正交投影之FIR迫零等化器及貝氏決定迴授等化器。貝氏決定迴授等化器被認為是消除符碼間干擾最好的方法之一。當非正交投影之FIR迫零等化器消除區塊間干擾後，再以貝氏決定迴授等化器消除符碼間干擾。我們利用位元錯誤率來比較系統效能。並在冗長資料量不足的情況下，與最小方均誤差區塊間干擾迴授等化器(MMSE-IBI-DFE)作比較。

All digital communication channels are subject to inter-symbol interference (ISI). To achieve the desired system performance, at receiver end, the effect of ISI must be compensated and the task of the equalizer is to combat the degrading effects of ISI on the transmission. Due to the demand of high data transmission rate, the multicarrier modulation (MCM) technique implemented with the orthogonal frequency division multiplexing (OFDM) has been adopted in many modern communications systems for block transmission. In block transmission systems, transmitter-included redundancy using finite-impulse response (FIR) filterbanks can be utilized to suppress inter-block-interference (IBI). However, the length of redundancy will affect the system performance, which is highly dependent on the length of channel impulse response. To deal with the effect of ISI, many equalizing schemes have been proposed, among them the FIR zero-forcing (ZF) equalizer with the non-orthogonal projector provides a useful transceiver design structure for suppressing the IBI and ISI, simultaneously.
In this thesis, we propose a new equalizing scheme; it combines the FIR-ZF equalizer with non-orthogonal projector as well as the Bayesian decision feedback equalizer (DFE) for IBI and ISI suppression. The Bayesian DFE is known to be one of the best schemes to achieve the desired performance for eliminating ISI. It can be employed to achieve the full potential of symbol-by-symbol equalizer. That is, after removing the effect of IBI with the non-orthogonal projector, the Bayesian DFE is employed for eliminating the ISI, simultaneously. For comparison, the system performance, in term of bit error rate (BER) is investigated, and compared with the minimum mean square error (MMSE)-IBI-DFE. The advantage of the new proposed equalizing scheme is verified via computer simulation under condition of insufficient redundancy.

Abstract i
Contents ii
List of Figures iv
Chapter 1 Introduction 1
Chapter 2 Block Transmission System 3
2.1 Introduction 3
2.2 Block Transmission Model 3
2.3 Decision Feedback Equalizer 9
Chapter 3 Block-based Equalization Using Nonorthognal Projector with Bayesian Decision Feedback Equalizer for CP-OFDM Systems 14
3.1 Introduction 14
3.2 Linear Equalizer Using Nonorthogonal Projector 14
3.2.1 The Properties of Nonorthogonal Projection 14
3.2.2 Linear Equalization Using Nonorthogonal Projector 18
3.3 Bayesian Decision Feedback Equalizer 22
Chapter 4 Computer Simulation 25
4.1 Introduction 25
4.2 Perfect Reconstruction 25
4.3 Performance of Different Receivers ( ) 27
4.4 Performance of Different Receivers under Minimum Redundancy 29
Chapter 5 Conclusion 32
Conclusion 32
Reference 34
Appendix A 36
Appendix B 38

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