分碼多工光纖網路使用錯誤更正碼之最佳化設計;Optimum Design of Optical CDMA Networks with Error Control Codes

[[abstract]]本計畫研究一使用錯誤更正碼(Error Control Codes,ECC)的同步分碼多工(Code Division Multiple Access,CDMA)光纖通信網路之最佳化設計。系統性能是以通道容量(Channel Capacity),及在某個誤碼率 (Bit Error Rate,BER) 下同時傳輸的用戶數目來加以評估。在相同的頻寬 (bandwidth expansion)下,我們研究隨機碼(pseudo random codes,PN codes)和錯誤更正碼的最佳組合方式。首先我們推導同步光纖CDMA網路使用Reed Solomon (RS) Codes之BER。其次在相同的頻寬下,我們分析最佳化的組合方式,並以Closed Form形式推導出最佳之編碼率(Optimum Code Rate),此最佳之編碼率可以表示成頻寬,用戶數和編碼長度(Block Length)的函數。這種採用最佳化設計的同步光纖CDMA網路,用戶數目會較多,通道容量更顯著的提升。我們評估用戶數目和通道容量提升的情形,也會分析隨機碼和RS Codes的最佳組合方式。 本計劃主要結果顯示最佳之編碼率介於0.45至0.53之間,此編碼率會隨著用戶數目增加而提高,並隨著頻寬增加而減少。但大體而言,其值約在0.5附近。;In this project, the optimum design of synchronous fiber-optic CDMA network with error control codes (ECC) is analyzed. The performance of the system is evaluated in terms of channel capacity and number of active users for a given bit error rate (BER). With the same bandwidth expansion factor, we analyze the optimum combination between pseudo random (PN) codes and error control codes. At first, we derive the BER of synchronous optical CDMA networks with RS Codes. Then the optimum code rate is derived in terms of length of PN codes, bandwidth expansion factor, and block length. In comparison with the results in the literature, the channel capacity of our system can be improved significantly, and the number of active users can also be increased greatly. Special emphasis is placed on the selection of code rates which leads to the optimal performance.[[note]]計畫編號:NSC88-2213-E146-002;研究期間:8708~8807;研究經費:282 千