The Application Of Ldpc Code In Optical Fiber Communication System

Error control coding technology is the main method which is used to improve the quality and reliability of the optical fiber communication system. At present, what the most commonly used as FEC in optical fiber communication system are Hamming code, BCH code and RS code, they have become ITU-T standard, service in commercial optical fiber communication system. LDPC code is a kind of FEC code, its function is close to shannon limit, and has very low bit error rate flat layer. Thus LDPC code caused more and more communication scholars’attention. LDPC code mainly applies to the wireless communication system, has now become wireless protocols, such as Wimax standards in IEEE802.16e. LDPC code are applied in many fields, such as image coding, deep empty space, storage, coding, the multiple-input and multiple-output (MIMO) system, etc..In recent years, LDPC code has been widely used in optical fiber communication system.This paper mainly devoted to how to add the module of LDPC code on the DQPSK and8DPSK modulation, direct detection of the optical communication system. Then we will analysis how to improve the performance and the tolerance of the system with chromatic dispersion (CD) and the first-order polarization mode dispersion (PMD). Then an improved of LDPC code is created which based on the PEG algorithm. This paper is mainly used matlab simulation platform and ISE software which is used on the Xilinx to realize the encoder. This paper discusses the main contents and the results are as follows: Built the optical transmission system with matlab on the DQPSK and8DPSK modulation format. At the same time, review the mechanism and the method of numerical calculation of CD and first-order PMD.Introduces the basic concept of LDPC code, H matrix description and the method of coding and decoding.Calculate the initial likelihood of LDPC code which will be applied to DQPSK and8DPSK modulation format with directly detection of the optical fiber communication transmission system. Observe BER and coding gain of LDPC code. From the results, when the BER is10-6, DQPSK and8DPSK modulation format through the LDPC code could separately had7.8dB and8.8dB of OSNR gain.Apply several different types of LDPC code (SCG-LDPC、LDPC based on distance distribution、π-rotation LDPC、block-LDPC and LDPC based on PEG algorithm)in optical communication system, from The redundancy of SCG-LDPC and LDPC based on distance distribution are low, which are less than10%and have the very high effectiveness. However, they need higher OSNR, about15dB.The redundancy of π-rotation LDPC, block-LDPC and LDPC based on PEG algorithm are higher. But the OSNR they need are lower, less than11dB, when their redundancy is50%.Construct an irregular LDPC code based on PEG algorithm. Compared with the regular type at the same redundancy, it can achieve0.7dB OSNR penalty.Use LDPC code to improve the performance of optical fiber communication system which exist CD and first-order PMD. The simulation results show that with a low OSNR penalty, LDPC code would achieve good BER performance when CD less than210ps/nm, PMD within the25ps on the optical fiber communication system.Apply ISE software on Xilinx realize an encoder of QC-LDPC code. Construct the encoder of the QC-LDPC code with Verilog in the simulation environment. The results are consistent with the simulation of matlab.