由於具有對多路徑傳輸的強韌性和高頻譜效率，使得正交分頻多工系統成為現代無線通訊的理想候選者。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)。為了避免信號受到區塊間干擾的影響，正交分頻多工系統採用冗餘碼(或保護區間)來保護我們的傳輸信號，常見的有循環前置碼(cyclic prefix)和補零冗餘碼(zero padding)兩種。
這篇論文提出一種新的虛擬隨機循環後置碼做為冗餘碼並且採用正交分頻多工調變配合多天線傳輸系統。虛擬隨機循環後置碼的主要特點為利用一組已知的循環碼去做通道估測，並且同時消除區塊間干擾。跟具循環前置碼正交分頻多工系統比較，虛擬隨機循環後置碼正交分頻多工系統克服了通道零點(channel null)的問題。此外，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，驗證我們所提出的方法。

Orthogonal frequency division multiplexing (OFDM) due to the robustness to the effect of multipath fading and having high spectral efficiency, it has become a good candidate of wireless communications systems. The block transmission of signal-blocks through the channel will suffer from the inter-block interference (IBI) and inter-symbol interference (ISI). Usually in the 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, which adopts the PRCP as redundancy and combines with multiple antennas. In fact, the multiple transmit antenna and multiple receive antenna, which exploits the spatial diversity, can be used to further enhance the channel capacity and achieve high data-rate. The main property of PRCP-OFDM modulation is that it exploits the cyclic-postfix sequences to estimate channel information with a low complexity method. Compared with CP-OFDM, it overcomes the channel null problem. For 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, as SNR grows, PRCP-OFDM can have better performance than PRP-OFDM. With the help of [9], [12] and [13], we extend the PRCP-OFDM to the MIMO case with space-time block coding. Via computer simulation, we verify that the performance is improved, in terms of the accuracy of channel estimation and symbol error rate (SER).

誌謝 i
中文摘要 ii
Abstract iii
Contents iv
List of Figures and Tables vi
Chapter 1 Introduction 1
Chapter 2 Pseudo Random Postfix OFDM Modulator in Multiple Antenna Systems 4
2.1 Introduction 4
2.2 ZP-OFDM System 5
2.3 MIMO PRP-OFDM System 11
2.3.1 MIMO PRP-OFDM Modulator and Demodulator 11
2.3.2 Order-One Channel Estimation 15
Chapter 3 Space-Time Block Coded OFDM Systems with Pseudo Random Cyclic Postfix 18
3.1 Introduction 18
3.2 System Model of Space-Time Block Coded PRCP-OFDM 19
3.3 Order-One MIMO Channel Estimation 27
3.4 Equalization of Space-Time Block Coded PRCP-OFDM 33
Chapter 4 Computer Simulation 37
4.1 Introduction 37
4.2 Channel Estimation for STBC PRCP-OFDM System 38
4.2.1 Complementary Cyclic Postfix Sequences Case 38
4.2.2 Orthogonal Cyclic Postfix Sequences Case 41
4.2.3 Non-Complementary Cyclic Postfix Sequences Case 44
4.3 Symbol Error Rate Performance of STBC PRCP-OFDM System 45
4.2.1 Complementary Cyclic Postfix Sequences Case 45
4.2.2 Orthogonal Cyclic Postfix Sequences Case 47
4.2.3 Non-Complementary Cyclic Postfix Sequences Case 48
Chapter 5 Conclusions 49
References 50

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