近年來隨著全球通訊與網際網路的發展，對於傳送訊號的傳輸速度、訊號品質以及資訊安全的要求也不斷的提升，這些一直以來都是大家廣泛討論的課題之一。因此利用光纖來當作傳輸的介質，不僅傳輸容量大，也因為傳輸環境單純使得訊號損耗較低且較不易受到電磁波干擾，另外由於訊號為點對點傳輸，大大的增加資料的保密性，因此光纖通訊被廣泛的使用在長距離傳輸以及都會骨幹網路等重要基礎建設。
在傳統的光纖通訊系統，由於當時DSP (digital signal processing)的技術還未成熟，故當時為了對傳輸通道做補償的方式大部分都是以光學的方式，但是缺點就是價格昂貴且架構複雜以及動態補償效果差，直到DSP技術成熟，大家轉而利用此較低成本的補償技術。
在本篇論文中，會先詳細介紹所使用的direct-detection OFDM系統，而產生訊號及解調訊號都是利用DSP，另外DDO-OFDM訊號在光場上傳送需要一根光載波，以利我們在接收端利用光檢測器將訊號由光場轉換成電場，但由於轉換到電訊號時會同時產生SSBI (Signal-Signal Beating Interference)而需要預留一個頻帶(gap)去避開此項干擾，也因為需要預留一個gap去避開這項雜訊，使得訊號傳送本身的頻寬效益會相對減少，故在此篇論文當中提出疊代演算法於接收端DSP中使用，利用這個演算法，我們可以有效的消除SSBI並且可以進一步的減少gap的使用，增加了頻寬效益且在減少gap的同時幫助我們消除SSBI的干擾影響來增加系統效能，在本篇論文中我們將疊代演算法實現於實作上，並以VPI模擬來幫助我們判斷改變系統參數的影響和探討。

With the growth of global communication and internet in recent years, the requirements for signal transmission speed, quality and information security are increasing; those above issues have been generally discussed for communication researchers. Therefore, by using fiber as the transmission medium, this not only increases transmission capacity but also reduces the signal loss and less susceptible to electromagnetic interference since the environment is simpler. In addition, information security can be upgraded because the signal transmit in the fiber is point to point. Thus, fiber communication is widely used in long-distance transmission and important infrastructure in the backbone of the network.
In the traditional optical fiber communication system, the transmission channel compensation methods are mostly via optical way since the DSP (digital signal processing) technology has not yet been mature. The disadvantage of traditional way is expensive, with complicated structure and poor dynamic compensation effect. We don’t turn to take advantage of this compensation technique with lower cost till DSP technology matures.
In this thesis, we will introduce our direct-detection OFDM system first and the OFDM signal will be generated by DSP. DDO-OFDM signal transmission in the optical field requires an optical carrier, which enable to convert the signal to electrical field via the photo detector at the receiver. However, when signal is converted to electrical field, the SSBI (Signal-Signal Beating Interference) will be generated simultaneously; we need to set aside one gap to avoid this interference. Because we need one gap between optical carrier, OFDM signal will decrease the signal spectrum efficiency. Therefore, in this thesis, we propose iteration algorithm which is used in DSP at the receiver. By using this algorithm, we are able to effectively eliminate SSBI and decrease the gap further; furthermore, to increase the signal spectrum efficiency and system performance. We implement iteration algorithm in the experiment and use VPI to discuss the impact of changing the system parameter.

摘要 ……………………………………………………………………………………Ⅰ
致謝 ……………………………………………………………………………………Ⅱ
目錄 ……………………………………………………………………………………Ⅲ
圖列表 …………………………………………………………………………………Ⅴ
表列表 …………………………………………………………………………………IX
第一章 正交分頻多工系統簡介 ………………………………………………………1
第二章 光學正交分頻多工系統 ………………………………………………………4
2-1 光學調變器原理 …………………………………………………………4
2-1-1 Mach-Zehnder Modulator ……………………………………….....4
2-1-2 IQ Optical Modulator ………………………………………............6
2-2 光學OFDM系統—直接檢測系統 ………………………………………7
2-3 Single-sided多頻帶直接偵測OFDM系統………………………………10
2-3-1多頻帶OFDM系統簡介…………………………………………..10
2-3-2多頻帶直接光學偵測OFDM系統 ………………………………11
2-3-3 Single-sided直接檢測光學OFDM系統傳送端與接收端介紹....12
第三章 數位訊號處理在正交分頻多工系統…………………………………………15
3-1 DSP實現OFDM訊號……………………………………………………15
3-2光纖色散與循環字首(Cyclic Prefix ,CP) ………………………………..18
3-3接收端同步(Synchronization) ……………………………………………20
3-4通道估測與通道補償 ……………………………………………………21
3-5 Decision-Directed Phase Noise Compensator (DD-PNC) …23
3-6 Error vector magnitude (EVM) …………………………………………...25
第四章 疊代技術演算法 ……………………………………………………………..27
4-1疊代演算法流程介紹 ……………………………………………………28
4-2多頻帶疊代演算法流程 …………………………………………………32
第五章 Single-sided band直接偵測OFDM系統模擬與實驗 ………………………35
5-1 One-band 系統 …………………………………………………………..35
5-1-1模擬環境與結果 ………………………………………………….35
5-1-2實驗流程與結果 ………………………………………………….39
5-1-3實驗與模擬結果比較 …………………………………………….46
5-2 Three-band 系統 ………………………………………………………...50
5-2-1模擬環境與結果 ………………………………………………….50
5-2-2實驗流程與結果 ………………………………………………….56
5-2-3實驗與模擬結果比較與結論 …………………………………….66
第六章 結論 …………………………………………………………………………..71
參考文獻 ………………………………………………………………………………..72

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