中文摘要：

分析了一种光码分多址（OCDMA）环网中码字消除结构,使用马尔科夫链模型和状态转移概率矩阵得出了环中各用户的误码率（BER）的表达式,计算表明,该码字消除结构虽然能够有效地把码字从环网中消除掉,避免码字在环网中循环产生干扰累加,但是会明显恶化经过码字消除结构的其它用户的BER性能;讨论了环网中用户的BER性能与码长、判决阈值的关系;针对码字消除对OCDMA环网的重要性,提出了一种基于BER监测及反馈的方法来降低码字消除结构造成的BER恶化,仿真结果表明,该方法能有效改善用户的BER性能。

英文摘要：

Code drop unit in OCDMA ring networks is analyzed. Expressions of BER performance of every users are obtained by using Markov Chain model and state transition probability matrix. The results show that even though code drop unit removes the code effectively from the ring network, it can also deteriorate the BER performance of other users who pass through it. The relation between BER performance and code length and code weight is analyzed in detail. Mter that,we propose a OCDMA ring network access control method which can improve the network＇s BER performance by BER monitoring and feedhack,with chip time control and codes random selection. Simulation result shows that the method can improve effidently the BER performance of users in the OCDMA ring network.