The Applications Of Ldpc Encoding And Decoding In High-Speed Optical Communications System

As the communications network is more and more integrated into the life, the high transmission rate has become the inevitable trend of communication system. And as the transmission rate surge, the ignored interference factors of the optical communication system before will not be ignored, the two important factors are the polarization mode dispersion (PMD) and nonlinear effects in the optical fiber.Forward error correction (FEC) technology can not only ensure quality of the transmission signal, and if combined with other technologies, it can also reduce the interference caused by the polarization mode dispersion and nonlinear effects. Because of the strong error correcting ability, low error layer etc advantages of low density parity check code (LDPC), it has become the representative of the new generation of FEC.In this paper, by joining the given bits (such as the initial value is set to "0", called as the watermarking bits) not only can estimate the channel information, but also can make use of the acquired channel information to optimized the initial information of the LDPC decoding algorithm.After the study of the optical communication system and the basic concept of LDPC codes, core work of this paper is as follows:1. Build and test the100Gb/s PDM-DQPSK simulation platform that contains the watermark insertion and extraction module. LDPC codes through the watermark insertion module, and are equally spaced added watermark. At received side, the received signals through watermark extraction module to estimate the channel information. Through the simulation test, simulation platform is available.2. Study the two important parameters of the channel estimation formula. Channel estimation formula can be optimized decoding algorithm of initial information, but the selection of two parameters in the formula is important. Through the simulation test, for a fixed length LDPC code word, it is concluded that the best watermark bit number should join the best values and the corresponding correction factors.3. Using the LDPC codes that inserted by watermark bits to improve the performance of the system. The improvement of the system can be studyed by the following several aspects:3.1From the bit error rate (BER) performance, the improved LDPC codes not only is better than the traditional LDPC code in BER performance, but also has better decoding efficiency.3.2Research the PMD and nonlinear anti-interference ability of the improved LDPC codes, the result shows that the improved LDPC codes have better ability to resist the PMD and nonlinear disturbance than the traditional LDPC codes.