Optimum Threshold Detection with a Pilot Wavelength in Optical Code-Division Multiple-Access Network

• Main Authors: Yi-Hsien Wang, 王譯賢
• Other Authors: Jen-Fa Huang
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/43885912595450865872

碩士 === 國立成功大學 === 電腦與通信工程研究所 === 95 === Optical code-division multiple-access (OCDMA) techniques not only provide a flexible and secure transmission but also allow multiple users access the network asynchronously and simultaneously. Therefore, they are the most suitable solution in local area network (LAN). In early one-dimensional (1-D) coding systems, the code length should be increased rapidly in order to accommodate large active users. Hence, the nonlinear effect will come into existence and the systems are hard to realize. Two-dimensional (2-D) coding systems have been introduced to improve the defect and they also maintain good correlation properties. In this thesis, we propose a new 2-D code family for OCDMA system called folded optical orthogonal codes (FOOCs). We fold the original 1-D optical orthogonal codes (OOCs) into the matrix form to produce FOOCs. FOOCs use two dimensions, i.e. time and wavelength, for transmission. According to our analysis, FOOCs have good correlation properties and can supply large number of codes. In the OCDMA system using FOOCs, we propose a novel and simple method to detect the active users. A special wavelength called pilot wavelength is added into the original transmission patterns of every user. At the receiver, therefore, we can acquire the number of the active users from the power of the pilot wavelength. Consequently, if we adjust the threshold value to the optimum threshold value according to the active users, we can decrease the bit error rate (BER) and improve the system performance.