Research On The Scheme Of Ldpc Encoding And Decoding In Ultra-High Speed Optical Communication System

The development of high-bandwidth technology, such as cloud computing, big data and so on, has made an explosive growth requests to the rate of Ethernet. As an important part of modern communication networks, ultra-high speed optical communication system entered a stage of development. In order to adapt to the rapid development of channel capacity in optical communication, a variety of high order modulation formats and various multiplexing technology have been widely used to improve the rate-to-bandwidth ratio of the system. However, with the increasing complexity of optical communication system, the increased OSNR requirements, reduced NCG and the crosstalk between codewords all will become apparent which affected the development of ultra-high speed optical communication system seriously. In order to improve the reliability of transmission signal and reduce the tolerance of receiver OSNR, all kinds of advanced optical communication technology including advanced modulation, detection technology, error correction coding technology and so on were proposed in succession. Inside which FEC and coherent reception technology have been widely used, and have proved to have outstanding performance.As an important FEC technology, several scheme of LDPC code used in high speed optical system have been widely studied in recent years. But all of the algorithms proposed LDPC algorithm do not consider the crosstalk among adjacency codewords involving by the knowledge of channel. This paper mainly devoted to the study of LDPC encoding and decoding in ultra-high speed optical system. Simulation result shows that the scheme can extract the channel knowledge by involving priori characteristic bits in the original LDPC can improve the system performance to a great extent.This paper discusses the main contents and the results are as follows:(1) We built the100Gb/s DQPSK modulation and direct detection optical communication system and100Gb/s ultra-high speed QPSK/16QAMmodulationand coherent detection optical system with Matlab. We also simulate the system performance of pre-FEC BER and post-FEC separately on the system above.(2) We study the decoding performance of low-density parity-check (LDPC) code based on Watermark scheme over100Gb/s DQPSK high speed direct detection optical communication system. We simulate the decoding performance of several group Watermark scheme under different water-mark bits number, and find the optimum percentage of water-mark bits for the Watermark scheme. The simulation shows that when BER performance drops to10"9, comparing with the traditional LLR-BPA, the optimum Watermark scheme gains a NCG improvement of0.5dB. The average number of decoding iteration number also decreases.(3) We deduce the LLR-BP decoding algorithm of LDPC over16QAM optical communication system in detail. We also propose the Watermark symbol auxiliary LDPC scheme and study the performance of the scheme in high-speed coherent optical communication system. The simulation shows that the modified Watermark scheme applies to16QAM coherent optical system also.(4) In summary, the main work of this paper focused on the study of Watermark scheme over ultra-high speed optical communication system. The scheme is a modify algorithm of LDPC code which is fit to the optical communication system of both DQPSK direct detection and the16QAM coherent reception which has an important significance to the future optical communication system.