分碼多重存取為多工技術一種，其中分碼多重存取在無線網路中有許多應用。由於光分碼多重存取系統擁有非同步存取以及高安全性的特性，所以光分碼多重存取在光通訊中是相當有吸引力的技術。

為了提昇光分碼多工系統的安全性，我們提出一個以陣列波導光柵為基礎的變換指配碼的架構以提昇整個系統安全性。變換指配碼概念為每位使用者分配不同數量的質數碼長複合碼，一次使用其中一組碼分別代表不同使用者。由於我們使用的質數碼長複合碼是由不同碼長的最大長度序列碼所建構出來的。所以其中的一些特性比如說循環特性或者是相關值都與最大長度序列碼有關。本論文也會根據碼的特性去設計適合的編解碼器。此外由中央控制中根據不同的網路狀況去控制變換指配碼的速率以提升安全性。

在本論文我們亦分析系統的安全性效能。藉由計算在光纖網路傳送碼型被竊聽的機率，我們可以量化傳送資料的私密性。由分析的結果可知，變換指配碼機制使得竊聽者能夠正確還原傳送的碼型的機會變的更加困難，因此資料的私密性因為變換指配機制而能夠有效提升。此外我們運用的質數碼長複合碼具有龐大指配碼的數量，能夠有效預防竊聽者對於所欲偵知的使用者進行暴力猜測法。

Optical code-division multiple access (OCDMA) is a multiplexing technique adapted from the successful implementation in wireless networks. Optical CDMA systems are getting more and more attractive in the field of all-optical communications as multiple users can access the network asynchronously and simultaneously with high level of security.

In order to enhance the security of OCDMA system, we propose array-waveguide grating (AWG) based scheme for confidentiality enhancement based on code reconfiguration mechanism. By exclusively assigning to each network user a set of pseudo-orthogonal composite M-signature codes and selecting one among them to represent each user’s signature. Because the composite M-signature code we use which is constructed by different code lengths maximum length sequence code. Some of the features such as cyclic shift properties or correlation are associated with the maximum length sequence code. This paper will base on code properties to design a suitable codec.

In this thesis, we also analyze the security performance of proposed system. Evaluating the probability of code word interception is quantified the degree of data confidentiality. The result shows that the probability of error-free code detection gets worse when we use the composite M-signature code and the eavesdropper processes code word detection more difficult, thus data confidentiality could be significantly increased. In addition, the proposed scheme using composite M-signature codes appears to be a promising coding type for generating OCDMA code space that are large enough to prevent successful brute force code search attacks.

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