- 學位論文
應用極化多工技術於混合式類比/數位通訊傳輸與光分碼多重擷取技術於自由空間光通訊之研究
Performance Analysis of Hybrid Analog/Digital Signal Transport and SAC-OCDMA with Polarization Multiplexing Scheme for Free Space Optics
摘要
本論文藉由整合光分碼多重擷取系統、極化多工系統技術及自由空間光通訊傳輸架構來達成同時傳輸類比及數位訊號的功能，此系統具備高傳輸速率、資料安全性以及低傳輸成本的好處。在此系統中，我們使用Walsh Hadamard codes(WHC)來做為基地站(Base Station, BS)的字碼(Codeword)，並且藉由每組WHC之間擁有固定互相關性質的特性，在接收端利用平衡檢測的方式來有效消除基地站之間的干擾。 在模擬軟體方面，本論文主要採用商業光通訊軟體Opitsysytem，並且透過Matlab採集數據及模擬。我們把光源做編碼，利用極化分光棱镜把光分為垂直光與水平光，透過馬赫曾德爾調變器(Mach-Zehnder Modulator, MZM)把數位訊號及類比訊號分別調變在垂直光與水平光上，極化合成之後把光利用自由空間光通訊(Free Space Optics, FSO)的方式傳出去。接收端的部分把光分成垂直光與水平光個別作解碼，之後利用光檢測器(Photo-detector, PD)做平衡檢測來消除多重使用者干擾(Multiple Access Interference, MAI)並且把數位訊號與類比訊號還原。 利用模擬軟體在單一使用者的探討背景時，當傳輸端的光源功率為7.5dBm，採用所提出的自由光通訊傳輸架構的方式，傳輸數位與類比訊號通道500公尺時，其錯誤率(Bit Error Rate, BER)小於3*10^-5。最後對於多基地站分析部分，我們使用數學理論推導的方式分別探討位元錯誤率與多使用基地站台間的關係以及位元錯誤率與有效接收功率等影響，於推導過程可知當使用OFDM技術傳輸，傳輸速率為2.5G時，有效接收功率(Psr)於-28dBm時，BER小於1*10^-5；當傳輸數位訊號，傳輸速率為2.5G時，有效接收功率於-20dBm時，其BER小於1*10^-10。OFDM訊號在40個BS時，BER為2.8*10^-9 ；數位訊號在10個BS時，其BER為1*10^-8。
並列摘要
With the development of the Internet, how to provide a high-speed and high-security comprehensive network has become urgent issue. In this thesis, we propose hybrid analog/digital transmission format scheme which integrated optical code-division multiple-access (OCDMA) and polarization multiplexing technique in free space optics (FSO) transmission. Orthogonal frequency division multiplexing (OFDM) transmits as the analog format and (on-off keying) OOK transmits as digital format in the study, respectively. In the proposed hybrid OCDMA system, it has high-speed transmission, signal security and low cost…etc. we adopt quasi-orthogonal Walsh-Hadamard codes (WHC) that with fixed cross correlation value as the codeword for each base station. With the property, the multiple access interference (MAI) can be efficiently eliminated by using the balanced detection scheme at the receive end. The simulation results of different source power and transmission distance are presented by commercial optical simulation software of Optisystem version 10, and data collection and simulation via Matlab. When the transmission side of the light power is 10dBm, the proposed FSO-OCDMA scheme can transmit digital and analog signals almost 300 meters when the bit-error-rate (BER) was less than 3*10^-5. Finally, the multiple base stations scenario, we use mathematical approach to theoretical analysis such as BER versus base station and BER versus effective received power. As the result, when using OFDM technology transfer, the bit rate at 2.5G, effective power from single source (Psr) at-28dBm, BER less than 1*10^-5; When the digital signal transmission, the transmission rate of 2.5G, the Psr at-20dBm, BER of less than 1*10^-10. OFDM signals in the 40 BSs, BER is 2.8*10^-9; digital signals in the 10 BSs, BER is 1*10^-8.