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研究生:林建宏
研究生(外文):Cheing-Hong Lin
論文名稱:具有非同調光源之光分碼多工系統之設計與分析
論文名稱(外文):Design and Analysis of Optical CDMA System with Non-Coherent Light Source
指導教授:吳靜雄
指導教授(外文):Jingshown Wu
學位類別:博士
校院名稱:國立臺灣大學
系所名稱:電信工程學研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2005
畢業學年度:93
語文別:英文
論文頁數:123
中文關鍵詞:多使用者干擾光分碼多工系統非同調光源相位引發強度雜訊
外文關鍵詞:multi-user interferenceOCDMAnon-coherent light sourcephase-induced intensity noise
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光分碼多工系統的研究從開始至今已經約有二十年的時間,此種系統的優點主要在於其可容許不同的使用者同時使用相同的頻帶,並且在傳送資料時可提供高度的資訊安全。光分碼多工系統的效能主要是受到多使用者干擾(multi-user interference, MUI)的影響,對於使用時域編碼之非同步光分碼多工系統(time-spreading asynchronous OCDMA)而言,多使用者干擾不但無法避免,而且會嚴重的影響系統整體之效能。近年來,由於具有非同調光源(non-coherent light source)之光分碼多工系統,可藉由編碼的方式來消除多使用者干擾,是以引發許多相關的研究。然而,由於非同調光源會產生相位引發強度雜訊(phase-induced intensity noise, PIIN),使得具有非同調光源之光分碼多工系統的效能受到嚴重影響。
傳統上具有非同調光源之光分碼多工系統主要分有三類,分別是同調多工系統(coherent multiplexing system)、頻譜振幅編碼系統(spectral-amplitude-coding system, i.e. SAC system)及二維頻譜/空間編碼系統(two-dimensional spectral/spatial coding system),為了提高具有非同調光源之光分碼多工系統的效能,本篇論文分別提出了三個新的系統架構以抑制由相位所引發之強度雜訊。就同調多工系統而論,我們所提出之系統係使用一脈衝寬頻光源(pulsed broadband light source)來取代傳統同調多工系統所使用之具有連續波之寬頻光源(continuous wave broadband light source),以降低各個使用者之信號碰撞的機率,並藉此抑制由相位引發之強度雜訊,以提昇系統之整體效能。
就頻譜振幅編碼系統而論,我們係提出了部分變異質數碼(partial modified prime codes)及對應之頻譜振幅編碼系統。其中,該部分變異質數碼係依據變異質數碼而推導出來的,是以其交叉相關係數(cross correlation)係小於或等於一。由於部分變異質數碼之交叉相關係數在大部分情況下是等於零,是以與其他頻譜振幅編碼系統相比,我們所提出之頻譜振幅編碼系統係具有較低之信號撞擊機率,故可進一步降低相位引發之強度雜訊所造成的影響。此外,藉由使用馬赫-曾德爾干涉儀(Mach-Zehnder interferometers),我們所提出之頻譜振幅編碼系統亦可完全消除多使用者干擾。
最後,為了改進二維頻譜/空間編碼系統的效能,我們提出二維完美相差碼(two-dimensional perfect difference codes)及其對應之二維頻譜/空間編碼系統。其中,該二維完美相差碼係依據一維完美相差碼而推導出來的,該一維完美相差碼原本係用於時域編碼同步光分碼多工系統(time-spreading synchronous OCDMA)之中。由於二維完美相差碼係具有一多使用者干擾相消特性(MUI cancellation property),並且其交叉相關係數係遠小於傳統之二維頻譜/空間碼,如最大面積矩陣碼(maximal-area matrices codes, i.e. M-matrices codes),是以我們所提出之二維頻譜/空間編碼系統可以同時除去多使用者干擾並抑制由相位引發之強度雜訊。此外,我們所提出之二維頻譜/空間編碼系統可容納之使用者個數,可隨著二維完美相差碼之空域碼長度增長而呈線性增加,目前傳統之二維頻譜/空間編碼系統仍無法達到此種效能。
依據數學分析及數值結果,本篇論文所提出之三種系統架構皆可有效的抑制由相位引發之強度雜訊並增加同時使用同一頻帶之使用者的數目。此外,我們亦使用一具有高度公信力的軟體工具”VPItransmissionMaker”,來驗證我們所提出之頻譜振幅編碼系統及二維頻譜/空間編碼系統的效能。
Optical code division multiple access (OCDMA) systems have been investigated for about two decades. They have the advantage of providing multiple users to simultaneously access the same bandwidth with high-level security. In general, the performance of OCDMA systems is primarily affected by multi-user interference (MUI), which is unavoidable for asynchronous time-spreading OCDMA systems. In recent years, OCDMA systems with non-coherent light sources attract a lot of attention because MUI can be completely eliminated by coding. However, in these systems, due to the nature of non-coherent light sources, a phase-induced intensity noise (PIIN) is caused and the system performance is hence degraded severely.
Conventionally, there are three categories of OCDMA systems with non-coherent light sources, i.e. coherence multiplexing system, spectral-amplitude-coding (SAC) system and two-dimensional (2-D) spectral/spatial coding system. This thesis aims to improve the performance of these systems. Regarding the coherence multiplexing system, a novel system structure is proposed in this thesis to suppress PIIN and improve the system performance thereby. In the proposed system, we simply substitute the continuous wave broadband light source of the conventional coherence multiplexing system with a pulsed broadband light source to reduce the probability of beating from other users. In this way, the PIIN caused by other users is suppressed.
As for the SAC system, we propose a family of newly constructed codes, named partial modified prime (PMP) codes, and a corresponding system structure. The PMP codes are a divided version of modified prime codes and thus have in-phase cross-correlation not larger than one. Because most of the in-phase cross-correlation between the PMP codes is zero, compared with the conventional SAC system, the beating probability of the proposed system is decreased considerably and thus the PIIN is further suppressed. Moreover, for elimination of MUI, Mach-Zehnder interferometers are employed in the proposed system.
Lastly, for performance improvement of the 2-D spectral/spatial coding system, we propose 2-D perfect difference codes and its corresponding system. The 2-D perfect difference codes are derived in view of perfect different codes that originally used in a synchronous time-spreading OCDMA system. Since the 2-D perfect difference codes have a MUI cancellation property and cross-correlation much lower than that of conventional 2-D spectral/spatial codes, such as Maximal-area matrices (M-matrices) codes, the proposed system can completely eliminate the MUI and effectively suppress the PIIN. Moreover, the number of simultaneous users that can be accommodated in the proposed system can be increased almost linearly in proportion to the spatial code length of the 2-D perfect difference codes. It is unreachable for present 2-D spectral/spatial coding systems.
In accordance with analysis and numerical results, all of the three proposed systems have better performance and can accommodate more simultaneous users than the conventional systems. In addition, the numerical results of the proposed systems using PMP codes and 2-D perfect difference codes are verified by using a well-known and highly recognized software tool, “VPItransmissionMaker.”
Table of Contents i
List of Tables iii
List of Figures v
Table of Abbreviations ix
Abstract xi

1. Introduction 1

1.1 Coherence Multiplexing System……………………………………………2
1.2 Spectral-Amplitude-Coding System…………………………………………7
1.3 Two-Dimensional Spatial/Frequency Coding System………………………14

2. Coherent Multiplexing System with a Pulsed Non-coherent Light Source 21

2.1 Synchronous System with Pulsed Non-coherent Light Source……………..22
2.2 Asynchronous System with Pulsed Non-coherent Light Source……………28
2.3 System Employing On-Off Keying Scheme………………………………...32
2.4 Summary…………………………………………………………………….38


3. Spectral-Amplitude-Coding Optical CDMA System Using Mach-Zehnder Interferometers 39

3.1 Partial Modified Prime Codes……………………………………………….40
3.2 SAC Optical CDMA System Using PMP Codes……………………………46
3.3 Performance Analysis……………………………………………………….49
3.4 Numerical and Simulation Results………………………………………….62
3.5 Summary…………………………………………………………………….70

4. Non-coherent Spatial/Spectral Optical CDMA System with 2-Dimensional Perfect Difference Codes 71

4.1 2-D Perfect Difference Codes………………………………………………72
4.2 Optical CDMA System using 2-D Perfect Difference Codes………………79
4.3 Performance Analysis……………………………………………………….85
4.4 Numerical and Simulation Results………………………………………….96
4.5 Discussions of Parameter Setting………………………………………….105
4.6 Summary…………………………………………………………………...108

5. Conclusion 111

6. References 117
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