隨著近代科技日新月異的快速發展，隨身行動裝置與大量的線上多媒體服務已成為時代的潮流，而為了支援高品質的影音多媒體服務等需求，提高無線接取網路的資料傳輸量則為現代通訊技術的一大挑戰。提高訊號載波頻率以及訊號傳輸的頻譜效率是增加資料容量的兩大關鍵。高頻訊號能夠帶來提供更寬廣的訊號傳輸頻寬，例如在60 GHz頻帶許多國家皆有約7 GHz的免授權頻帶，然而，如此高頻的訊號無論在傳統電纜線及大氣中皆會遭受相當大的傳輸損耗，導致傳輸距離受限。本論文採用光載微波無線系統利用光纖作為中央控制台(Central Station, CS)與遠端基地台(Base Station, BS)之間的傳輸媒介來傳輸高頻的正交分頻多工訊號，除了使得單一通道之頻譜效益得以最大化，且能夠以低能量損耗傳輸高頻訊號，藉以增加訊號傳輸距離。
多天線輸入多天線輸出技術是另一個增加頻譜效益的關鍵技術。利用額外增加的發射與接收天線，並傳送各自獨立的訊號於各發射天線，無線訊號佔用的頻譜得以在同一時間被重複利用，從而增加資料容量。本團隊先前曾提出以強度調變與直接偵測 (Intensity Modulator with Direct Detection, IMDD)為基礎的光載微波無線系統，其架構雖然簡單，但受光纖色散導致的能量衰減使使得光纖傳輸距離只有500公尺，後來改以單極馬氏調變器(Single-drive Mach-Zehnder Modulator, SD-MZM)為基礎，藉由控制訊號和載波的頻率，可以減少光纖色散所帶來的影響，但為了避免拍擊干擾，使得可控制的頻率範圍選擇有限，光纖傳輸距離只能傳輸4公里。
本論文透過適當選擇訊號和載波頻率降低光纖色散導致的能量衰減程度，並利用拍擊干擾消除技術解決其對訊號品質之影響，成功使得光纖傳輸距離達到12公里。除此之外，多天線輸入多天線輸出技術搭配動態位元存取技術的使用也使得訊號能夠以最有效的能量分布在通道中傳輸，從而增加資料傳輸量，達到最大56 Gb/s。

With the explosive grow of modern technology, mobile devices along with high quality multi-media services have grown beyond imagination. In order to match the demand of high speed interactive multi-media mobile applications, improving wireless network capacity is considered great challenge to modern communication technology. The key points toward multi-gigabits communications are to increase bandwidth and spectral efficiency of communication system. Higher carrier frequency provides much more bandwidth. For instance, around 60-GHz band, 7 GHz bandwidth has been declared licensed-free by several countries. However, higher carrier frequency signal suffers high transmission loss in both conventional cable and air-link transmission and leads to a limitation on transmission distance. In this thesis, Radio-over-Fiber (RoF) system is used to distribute Orthogonal Frequency Division Multiplexing (OFDM) signal from central station (CS) to base station (BS). Taking advantage of the characteristic that subcarriers of OFDM signal are orthogonal to each other, the 7 GHz bandwidth can be used more efficiently. Moreover, high frequency signal can enjoy low transmission loss with utilizing fiber as transmission medium.
Multiple-Input Multiple-Output (MIMO) technology is another critical technique to improve spectral efficiency. By adding numbers of transmitter and receiver antennas and deliver independent signal through each transmitter antenna, data throughput can be increased because of the reuse of spectrum at the same time. Our group has successfully demonstrated simple RoF system using intensity-modulation direct detection scheme using electrical-absorption modulator (EAM). Although the architecture was simple, the fiber transmission distance is limited to 500 m by strong dispersion induced power fading. The single-drive mach-zehnder modulator (SD-MZM) is used to replace the EAM for being a more efficient modulator for the system. By adjusting the signal frequency and beating carrier frequency appropriately, the fiber transmission distance can be extended. However, in order to avoid signal-to-signal beat interference (SSBI), the extended distance is only 4 km. In this thesis, the frequency arrangement is selected appropriately to reduce dispersion induced power fading and the fiber transmission distance is successfully extended to 12 km. The integration with MIMO technology and the use of bit-loading algorithm further improve the spectral efficiency and achieved utmost data rate of 56 Gb/s at back-to-back transmission.

Acknowledgements i
中文摘要 i
Abstract iii
CONTENTS v
List of Figure viii
Chapter 1 Introduction 1

1.1 Background 1
1.2 Motivation 3
1.3 Object and Problem 4
Chapter 2 Literature Review 6

2.1 Preface 6
2.2 Optical Communication System 6
2.2.1 Optical Transmitter 6
2.2.2 Optical Modulator 7
2.2.3 Theoretical Derivation of SD-MZM 8
2.3 RoF System using External Modulator 14
2.3.1 Architecture of DSB RoF 14
2.3.2 Architecture of DSBCS RoF 15
2.4 Orthogonal Frequency Division Multiplexing 17
2.4.1 Why OFDM 17
2.4.2 Concept of OFDM 18
2.4.3 The Advantage of OFDM 20
2.4.4 The Disadvantage of OFDM 21
Chapter 3 Concept of Proposed System 23
3.1 Preface 23
3.2 Fiber Induced Fading and Signal-to-Signal Beat Interference 23
3.3 SSBI Mitigation algorithm 27
3.4 Training Symbol Design 28
3.5 MIMO Technology 29
Chapter 4 DSP Technique of Proposed System 33
4.1 Preface 33
4.2 MIMO-SSBI Mitigation Algorithm 33
4.3 I/Q imbalance Compensation 38
4.4 Bit-loading Algorithm 41
Chapter 5 Experimental Demonstration of Proposed System 45
5.1 Preface 45
5.2 Experimental Setup 45
5.3 Experimental Results for MIMO-OFDM QPSK 48
5.3.1 SNR Results versus Various CSPR 48
5.3.2 BER Results versus Various PD Received Power 51
5.4 Experimental Results for MIMO-8QAM QPSK 53
5.4.1 SNR Results versus Various CSPR 53
5.4.2 BER Results versus Various PD Received Power 54
5.5 SNR Results Within Signal Bandwidth 56
5.6 Experimental Results for MIMO-OFDM Bit-loading 58
Chapter 6 Conclusion 60
References 61

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