在現代的長距離通訊時，勢必得採用光通訊網路以應付大數據、影音等資料交換。近年來，光通訊網路中較常被探究的為光分波多工(Wavelength-Division Multiplexing, WDM)、跳頻/展時(Wavelength Hopping/Time Spreading, WH/TS)及光分碼多重截取(Optical Code-Division Multiple-Access, OCDMA)，這三者皆被視為是區域網路的最佳選擇，其中，後者優點更包括：可非同步傳輸、保密性高、網路設計較有彈性等等。

然而當分碼多重截取的概念應用在網路架構時，各個使用者間的多重截取干擾(Multiple Access Interference, MAI)便會大幅影響系統效能。因此我們提出兩種解決方案，具備MAI消除機制的跳頻/展時光網路架構與結合光分波概念的同心圓光分碼多重截取網路。

在跳頻/展時光網路中，我們設計兩種碼型為基底並以完全互補碼為基礎，即便設計出的完全質數位移碼(Complete/Prime/Shifted code, CPS)使得編解碼概念更加複雜，但整體系統的最大使用者數目也大幅提升，且多重截取干擾得以完全消除。而對應設計的編解碼器在硬體也更加以簡化；而在第二種光分波/分碼多重截取網路中，我們使用分波段的概念及同心圓規劃將整體使用者數量切割，以此降低網路硬體的負擔。我們也針對同心圓網路去設計不同群組間的溝通方式，且更有效的控制彼此傳輸時間。而所設計的延申最大碼長序列(Extended M-Sequence code, EMS)則具備了靈活度高、低交相關性、自循環等等特性，在簡化硬體設計上有很大的幫助。

另外我們也探討其它方式來降低在光/無線通訊的錯誤率，商業實務上，包括WiFi 802.11n/ac或WiMAX等皆已經導入低密度位元檢查碼(Low-Density Parity-Check code, LDPC)來達成目標，然而地板效應(error floor)會限制住低密度位元檢查碼的效能，因此，我們去設計一種骨架矩陣(skeleton matrix)來改善查核矩陣(parity-check matrix)的結構。動機在於藉由這種骨架矩陣去降低查核矩陣中可能最小週長(girth)數目。骨架矩陣不僅有效且系統地分散了查核矩陣的組合，且保持了原先的最小週長。由模擬結果得知，我們提出的方式可有效改善現有文獻中的低密度位元檢查碼的效能。

In long-distance transmission networks, one effective solution to handle big data and information transmission is utilizing optical fiber communication systems. Recently, Wavelength-Division Multiplexing (WDM), Wavelength-Hopping/Time-Spreading (WH/TS) and Optical Code-Division Multiple Access (OCDMA) are getting more attractive over local area network. Especially of the OCDMA systems, having some advantages, suck like asynchronous transmission, security in transmission, flexibility in network design.

However, the multiple access interference (MAI) caused from each user become a major issue, since it generally decreases the performance of CDM network. Therefore we propose two solutions, an optical WH/TS network with MAI cancelation and a concentric WDM/OCDMA network.

In optical WH/TS network, we propose a completely prime shifted code (CPS) composed of three different sequence families. It enlarges the cardinality of proposed WH/TS system and eliminates the MAI. In additional, the hardware designs of encoder/decoder are also reduced. In second solutions, a WDM/OCDMA utilizes concentric-circles topology to divide optical network units (ONUs) into different groups. It not only give that the optical line terminal (OLT) can preserve a well round-trip transmission time, but also lower the hardware loading of each group. A proposed extended M-sequence code (EMS) is also designed with several properties, such as high flexibility, low cross-correlation and cyclic shifted.

In additional, we also seek another solution on improving the bit error rate (BER) over optical/wireless communication. The low-density parity-check (LDPC) codes have been selected to be a standard of 802.11n/ac and WiMax. Since an error floor limits the performance of regular quasi-cyclic (QC) LPDC codes, we propose a so-called "skeleton matrix" to modify the structure of the parity-check matrix. A motivation is to reduce the possible short-cycles in regular parity-check matrix. The skeleton matrix not only systematically disrupts positions of parity-check matrix, but also maintains previous girth of codes. Simulation results show that proposed QC-LDPC codes improved can overcome the previous error floor performance.

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