Research On Long-distance Transmission Technology Based On Coded-modulation In PTN System

To meet the rapid evolution of smart-grid and the proposition of energy-Internet,the transmission capacity of power communication network should be promoted rapidly.The business properties of packet and all-IP require the transmission network(TN)to have a large ability of IP-carrying.The line capacity has been developed from 10GE to 40GE/100GE/200GE and should be adapted to the characteristics of long-distance transmission of ultra-high voltage line.The single span length of 10G optical system has been over 400 km.With the trend of business diversification,IP-based and intelligent,packet transmission network(PTN)technology will become the important technology in the backbone and convergence layers of the communication network.Forward error correction(FEC)and the coherent receiving technique based on high order modulation are the two keys to improve the speed and distance of PTN System.Low-density parity-check(LDPC)code is a kind of FEC code with excellent performance,and high order modulation technology can improve the system transmission rate.Based on LDPC code and high order modulation,this thesis studies the high-speed long-distance transmission technology of the PTN system.In addition,the construction of the quasi-cyclic LDPC codes and the realization of the high-order modulation have been investigated.The coherent optical system with LDPC-coded modulation is constructed based on the simulation flat.The main works are as follows.(1)A construction method of quasi-cyclic(QC)LDPC code based on finite field is proposed in this thesis and the detailed construction method of the check matrix is given.Compared with the LDPC code in 802.3a standard,the simulation results show that the proposed LDPC code has higher transmission efficiency and the better error-correction performance.Furthermore,the net code gain(NCG)is improved by around 0.26dB at the BER 10-5.At the same time,the proposed check matrix has the characteristic of QC,which is more convenient for the design and implementation of encoder and decoder.(2)Based on the study of binary QC-LDPC code and finite field,a construction method of non-binary(NB)QC-LDPC code is proposed.The simulation results show that the NCG of the constructed NB-LDPC code is 1.5dB more than that of LDPC code in IEEE802.16e standard at the BER10-4.Besides,NB-LDPC code has the better ability to combine with high order modulation.(3)The high-order modulation method of coherent optical communication(COC)system is studied.With the introduction of principles of QPSK and 16QAM modulation,the realization and simulation based on dual-drive Mach-Zehnder Modulator(DD-MZM)are presented in the Opti System simulation flat.Furthermore,16APSK modulation with circular constellation has a much greater minimum distance than 16QAM modulation with square constellation.In this thesis,the mapping relation between the input and output signals of DD-MZM and bit sequence is given and a method to realize the optimal 16APSK modulation signal with low complexity in COC system is proposed.(4)The constructed QC-LDPC code is applied to the COC system.Based on the Opti System environment,the 100G DP-QPSK COC system is built with FEC coded-modulation,which includes FEC encoder,DP-QPSK transmitter,transmission line,coherent receiver,DSP processing,detection and FEC decoder,etc.The principle of each module and the simulation results of the system are given.The simulation results show that the NCG of the proposed QC-LDPC code is 0.8dB more than that of RS(255,239)code at the BER 10-4.