Research Of Optical Code Division Multiple Access Network Based On Ring Topology

Optical Code Division Multiple Access(OCDMA) has been one of the key research directions for future all-optical access for supporting random and asynchronous access, natural high security and confidentiality , efficient network management and so on. Traditional OCDMA network is based on star topology and can't achieve code reusability because of its working style of broadcasting. When the users accessing become more , multi-user interference(MUI) is serious, and the system performance of BER degrades obviously. So such a topology limits the number of users accessing to the network simultaneously and makes the detection more difficult because the signal energy is too scattered . Also such a topology has a natural defect because there is single-user transmission inevitably which can increase the probability of code interception. Aimed at these disadvantage , OCDMA network of ring topology ,another kind of topology, is studied. The main work in this thesis is as follows:1 .Construction and realization of OCDMA address code are introduced systematically. For MUI impacts the performance of OCDMA systems mostly , the effects of MUI on system performance of BER when using different codes are studied at first, which paves the way for following research of MUI characteristic of network traffic.2. A model of unidirectional two-fiber ring based on code routing is presented. The throughput performance under static traffic and the congestion performance under dynamic traffic based on this model are studied , and compared to wavelength division multiplexing(WDM) network of the same structure. The results indicate OCDMA ring network gives a better performance than WDM nework under the condition of same wavelength resources , and the performance is even better when a good address code is selected.3. A novel code conversion structure is presented . The application of code conversion in ring OCDMA network is researched through simulation . The results show introduction of sparse code conversion to the network improves the congestion performance.4. The security of OCDMA network of ring topology under static and dynamic traffic are studied and the results show that the security of ring network under static traffic depends on the network size, while on the nummber of address code available in the network under dynamic traffic.