正交分頻多工系統(OFDM system)適用於許多無線通訊並保有傳輸速度快的特性。當區塊式的訊號在通道中傳輸時，這些訊號會因通道的影響而遭受符碼間干擾(inter-symbol interference)和區塊間干擾(inter-block interference)。而正交分頻多工系統則是採用了冗餘碼(或保護區間)來隔開區塊式的訊號，使訊號避免受到區塊間干擾。而傳統的兩種作法是使用循環前置碼(cyclic prefix)和補零冗餘碼(zero padding)來當作冗餘碼來應用。
本篇論文提出一種新的虛擬隨機循環後置碼(PRCP)做為冗餘碼且使用一種名為MERRY演算法[18]的盲蔽式通道縮減演算法來避免在冗餘碼長度小於通道階數時產生的區塊間干擾，並採用正交分頻多工調變配合多天線傳輸(MIMO)系統來增加通道容量和傳輸速度。虛擬隨機循環後置碼的主要用途為利用一組已知的循環碼來做通道估測，並且可使用同一組冗餘碼來消除區塊間干擾。跟循環前置碼來做比較，虛擬隨機循環後置碼解決了通道零點(channel null)的問題。而對於補零冗餘碼正交分頻多工系統來說，虛擬隨機循環後置碼正交分頻多工系統利用了補零冗餘碼那段額外的資訊去估測通道。更重要的是，虛擬隨機循環後置碼正交分頻多工系統避免了在虛擬隨機後置碼正交分頻多工系統中，進行通道估測時所遭遇的來自訊號的干擾。因此，隨著信號雜訊比(SNR)的提升，我們的方法可以有較好的表現。此外，由於多天線系統可以提供更高的傳輸率和維度增益(diversity gain)，所以我們將虛擬隨機循環後置碼正交分頻多工系統結合時空區塊碼(space-time block code)延伸至多天線傳收的情況下藉著參考文獻[9]，[12]和[13]的幫助。最後，我們可以由電腦模擬的結果來驗證我們所提出的方法。

The Orthogonal frequency division multiplexing (OFDM) modulator with redundancy has been adopted in many wireless communication systems for higher data rate transmissions .The block transmission of signal-blocks through the channel will suffer from the inter-block interference (IBI) and inter-symbol interference (ISI). In the traditional transmitter of the OFDM systems, redundancy (or guard interval), such cyclic prefix (CP) or zero padding (ZP), with sufficient length, is inserted in the transmitted block to avoid the IBI. In this thesis, we propose a novel pseudo random cyclic postfix (PRCP-) OFDM system configuration and joint a blind channel shortening algorithm which named MERRY algorithm [18], which adopts the PRCP as redundancy and combines with multiple antennas. In fact, the multiple input and multiple output (MIMO) system, which exploits the spatial diversity, it can be used to further enhance the channel capacity and achieve high data-rate, and we extend the PRCP-OFDM to the MIMO case with space-time block coding. In redundancy insufficient case, the blind channel shortening algorithm be adopted for suppressing the IBI. The main property of PRCP-OFDM modulation is that it exploits the cyclic-postfix sequences to estimate channel information with a low complexity method. For CP-OFDM, it overcomes the channel null problem. Compared with ZP-OFDM, it uses the additional information to estimate channel which is replaced by zero samples in ZP-OFDM. Moreover, PRCP-OFDM avoids the interference of signals to the desired postfix when we estimate channel impulse response (CIR) and which is different from pseudo random postfix (PRP-) OFDM [8]. Thus, when SNR grows, PRCP-OFDM can have better performance than PRP-OFDM. With the help of [9], [12] and [13]. Via computer simulation, we verify that the performance is improved.

Acknowledgements .i

Abstract .ii

Contents iii

List of Figures and Tables v

Chapter 1 Introduction 1

Chapter 2 Pseudo Random Postfix OFDM Modulator in Multiple Antenna Systems 4

2.1 Introduction 4
2.2 MIMO PRP-OFDM System 5
2.21 MIMO PRP-OFDM Modulator and Demodulator 5
2.2.2 Order-One Channel Estimation 9
2.3 The MSSNR TEQ 12
Chapter 3 Space-Time Block Coded OFDM Systems and channel shortening with Pseudo Random Cyclic Postfix 14

3.1 Introduction 14
3.2 System Model of Space-Time Block Coded PRCP-OFDM 15
3.3 The blind channel shortening algorithm 22
3.4 Order-One MIMO Channel Estimation 24
3.5 Equalization of STBC PRCP-OFDM 29
Chapter 4 Computer Simulation 33

4.1 Introduction 33
4.2 Channel Estimation for STBC PRCP-OFDM System 34
4.2.1 Orthogonal Cyclic Postfix Sequences Case 34
4.2.2 Non-orthogonal Cyclic Postfix Sequences Case 38
4.3 Symbol Error Rate Performance of STBC PRCP-OFDM System 39
4.2.1 Orthogonal Cyclic Postfix Sequences Case 39
4.2.2 Non-orthogonal Cyclic Postfix Sequences Case 40
4.4 Blind Channel Shortening of STBC PRCP-OFDM System 41
Chapter 5 Conclusions 45

References 47

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