Spatial/Spectral OCDMA System Using Partial Modified Prime Code and Error Correcting Code

分碼多工技術在現今的通訊領域裡面佔有很重要的地位。在無線通訊領域裡面，它擁有許多優點，包含多工接取、抗干擾、高安全性、非同步傳輸、抗多重路徑、支援多速率傳輸等，所以有很好的發展；在光通訊領域裡面，許多應用分碼多工技術的光分碼多工系統也逐一被研究，漸漸受到重視。 早期提出的光分碼多工網路主要是針對經過編碼後的非同調光波來設計，所使用的光正交碼的互相關函數很大，可選擇的正交碼種類不多，正交碼的數目也不多。最近，許多新的利用頻譜振幅編碼的光分碼多工系統相繼被提出。這些在頻譜編碼的設計免除了在同調系統需要的高速電子處理元件的複雜度。當我們使用具有固定大小的同相互相關函數的序列來編碼時，多重使用者的干擾可以被消除，可是在這些頻譜編碼光分碼多工系統中，由於使用寬頻光源，它發出的光波強度震盪會造成相位引發強度雜訊，這雜訊對系統效能的影響非常嚴重。 除此之外，為了增加使用者的數量，許多二維編碼的設計也頗受注意。在這些二維編碼的系統中，有一種是在空間及頻譜上編碼的光分碼多工系統，它除了擁有上述頻譜編碼系統的優點，也可以增加在特定效能的要求下可允許的使用者數目。由於目前光纖的價格較為便宜，因此這種利用多光纖來架構的空間及頻譜編碼的系統確實是可以實現的架構。 在此篇論文中，我們提出了一個新的空間/頻譜二維編碼的光分碼多工系統架構，在此架構中並結合了錯誤更正碼的技術。這個系統中使用了部份變異質數碼，根據此碼的互相關函數特性，可以避免多重使用者的干擾，所以進一步減少了相位引發強度雜訊。除此之外，因為在頻譜使用了錯誤更正碼的編碼，使的效能可以更加提升；比起前人設計的系統，我們雖然使用了錯誤更正碼，但是並沒有額外增加頻寬的需求。最後的分析結果顯示，我們的系統在資料傳輸率達10Gbps時，位元錯誤率可以降到 以下。比起其他的二維光分碼多工系統，我們提出的系統在高速環境下比較可行，而且結構複雜度低。Code division multiple access (CDMA) plays an important role in communications technologies nowadays. In mobile communications, it has been well developed due to its advantage of multiple access, anti-jamming, high-level security, asynchronous transmission, multi-path resistance, and multi-rate transmission. In all-optical communications, many optical CDMA (OCDAM) systems are proposed and getting more and more attention. The early OCDMA network proposals were based on coded sequences of noncoherent pulses. The used optical orthogonal codes (OOCs) generally have poorer correlation properties and limited code size. Recently, several alternative OCDMA schemes based on spectral amplitude coding (SAC) have been proposed. These proposals do not require the complexity of coherent system. SAC OCDMA systems can cancel the multiuser interference (MUI) by employing the code sequences with fixed in-phase cross correlation. However, the phase-induced intensity noise (PIIN) due to the intensity fluctuation of the broadband light source (BLS) still severely affects the system performance. Another issue is to support a large number of simultaneous users, thus two-dimensional (2-D) coding schemes attract a lot of attention. Among those schemes, spatial/spectral coding OCDMA has the advantage of SAC coding scheme while the maximum number of users under a specific performance can be increased. Because fibers are inexpensive nowadays, spatial/spectral coding scheme is a realizable solution. In this thesis, we propose a new system architecture of spatial/spectral coding 2-D OCDMA systems combining with error correcting codes (ECC). The scheme of using partial modified prime (PMP) codes can completely eliminate the MUI due to its zero cross-correlation property. And the PIIN can be suppressed. Further more, the system performance is improved by employing ECC on spectral domain while no additional wavelength is needed comparing to the conventional 2-D OCDMA system using PMP codes. The results show that data bit error rate can be as low as at data rate of 10Gbps. Compared with other 2-D OCDMA systems, our proposed system is much simpler and has better performance without any extra wavelength.摘要..............................................................................................................................i List of Tables................................................................................................................v List of Figures............................................................................................................vii Abstract……………………………………………………………………………...xi Chapter 1 Introduction..............................................................................................1 1.1 Motivation…………………………………………………………………..1 1.2 Outline of The Thesis……………………………………………………….2 Chapter 2 Overview of Some Optical CDMA Systems...........................................3 2.1 Multiple Access Techniques in Optical Fiber Networks……………………3 2.2 One-Dimensional Spectral-Amplitude Coding OCDMA Systems…………5 2.3 Two-Dimensional Spatial/Spectral Coding OCDMA Systems……………..9 Chapter 3 The Proposed System..............................................................................17 3.1 Partial Modified Prime Codes…………………………….………………..17 3.2 Error Correcting Code ……..…………………………….……………….. 20 3.3 System Architecture………………………………………………………. 22 Chapter 4 Performance Analysis and Numerical Results.....................................29 4.1 Assumptions………………………...………………….…………………..29 4.2 Formulation of Photocurrent Variance……...………….…………………..29 4.3 Bounds of Error Correcting Code……………...……….………………….35 4.4 Parameters and Numerical Results ..........……….…………………………37 Chapter 5 Discussion.................................................................................................45 5.1 Performance of Different Thresholds……………....………………………45 5.2 Comparison of Using APDs and PINs...........................................................49 5.2 Bit Rate Limitation…………………………………………………………53 Chapter 6 Conclusions..............................................................................................55 Appendix....................................................................................................................57 References..................................................................................................................6