高速光纖系統應用波長編碼之研究

Abstract

錯誤更正碼在高速光纖通訊系統中尚未被廣泛使用, 其原因如下: 1) 編 碼通常會改變系統的傳輸速率, 2) 編碼所需的訊號處理過程在高速光纖 通訊系統上很難完成。3) 編碼所得的效益在光通訊系統``功率-限制''模 式下很低。在本篇論文中, 我們提出一種應用光通訊波長領域,並列式,頻 道間的錯誤更正碼系統 -- 波長編碼系統。此種方法不同於傳統串列式編 碼系統而可提供許多優點。首先，資料完全未被編碼過程改變，使得波長 編碼系統極適用於實際的光纖通訊系統。其次，波長編碼系統的編碼方式 較串列式編碼系統簡單。與串列式編碼系統比較之,波長編碼系統 可以大 量地減少編碼器及解碼器的數量。再者，波長編碼系統在光 纖通訊系統 ``波散-限制'' 操作模式下可以提供無限大的編碼增益。最後, 波長編碼 系統可以更正發生在一個頻道上的成串錯誤。 然而, 波長編碼系統受限 於資料編碼數目而無法於少量資料頻道的環境中有效使用。我們於第三章 提出另一種改良式的波長編碼系統。改良式波長編碼系統保有絕大部份波 長編碼系統的優點,並可將同位元檢查頻道的數目由原波長編碼系統的 r 個降低到一個,因而大大地提高了同位元檢查頻道的效率。另外, 改良式 波長編碼系統亦提供更彈性化的編碼方式而能滿足使用者的需求。 FEC are rarely used in practical lightwave systems because: 1) coding in general changes system bit rate, 2) the required signal processing in encoding/decoding processes is difficult in high-speed lightwave systems, and 3) coding gain is small in power-limited lightwave systems. Nevertheless, some practical applications of forward error correction (FEC) code at the rate of DS-3 and STS-1 are presented by Grover and Moore. They intelligently put the parity-check bits in the unused stuffed bits and unassigned overhead fields in DS-3 and STS-1 in order not to alter the system bit rate. However their approaches demand accurate timing control and complicated coding processes, therefore they can only be implemented at the STS-1 level. We propose an interchannel parallel coding scheme in the wavelength domain--the WDM coding system. The system differs from usual serial coding systems and provides many advantages. First, data channels are completely unaltered in the coding Secondly, parallel encoding/decoding are simpler than those of coding systems.Thirdly, comparing to serial coding, WDM coding is able to reduce heavily the number of encoding/decoding pairs. Finally, WDM coding systems could correct single channel burst We have evaluated the system performance and analyzed the system limitation imposed by bit-skew among wavelength channels. To reach an efficient and flexible WDM coding system, we further propose a modified WDM coding system with single parity-check channel in Chapter 3. The system provides most of the advantages of original WDM coding systems and can much increase the of the parity-check channel. We have evaluated the system and analyzed the performance of frame synchronization needed for modified WDM coding system.