Performance Analysis of Synchronous and Asynchronous Wavelength-Time Spreading Codes for Optical CDMA Systems

• Main Authors: Hsiao-Wei Hu, 胡曉偉
• Other Authors: Guu-Chang Yang
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/53739207365167970798

碩士 === 國立中興大學 === 電機工程學系所 === 94 === In this thesis, we propose a “synchronous” wavelength-time optical code-division multiple access (OCDMA) scheme using two-dimensional (2-D) Walsh-based bipolar–bipolar code, in which Walsh code sequences are used for time spreading, in place of Barker sequences used in our previously proposed “asynchronous” bipolar– bipolar code. The new synchronous coding scheme supports larger cardinality and better performance than the asynchronous scheme because Walsh code has larger cardinality than Barker sequences and a zero cross-correlation property, in the expense of requiring system synchronization. One potential application is future CDMA-based passive optical networks (PONs), in which synchronous downstream traffic uses the Walsh- based bipolar-bipolar code and asynchronous upstream traffic uses the Barker-based counterpart. Since the new code is modified from the original code, the same hardware can be used for both directions of traffic. Besides, we also compare the bipolar-bipolar code with the bipolar-unipolar code with and without hard-limiting.