An Enhanced LDPC Based Differential Iteration Decoding Scheme For Coherent Optical Communication Systems

At present,with the rapid development of high-definition video,interactive multimedia and other data services,people make more demands on the signal transmission rate of the system.In optical communication,coherent detection has become a research hotspot because of its higher speed and better performance compared to direct detection.In the coherent optical communication system,the application of digital signal processing to dispersion,nonlinear compensation,and control,to a large extent,improves the spectral efficiency of the system.In addition,the polarization division multiplexing technology is introduced into the system of coherent detection,which improves the transmission capacity of the system.In coherent optical communication,the amplitude and phase of the optical signal can be modulated.The use of the high order amplitude and phase modulation format can greatly improve the spectral efficiency of the system,thus high rate optical fiber communication system is achievable.The main work of this paper is as follows:1.In order to suppress the noise and nonlinear impairments of the optical fiber channel,a method based on DFT-spread technology for reducing the PAPR of OFDM signal is studied.The simulation is carried out in the cohere nt optical communication system with the transmission rate higher than 100Gbit/s.The modulation format of the signal transmitted in the system is M-QAM along with OFDM.This method improves the accuracy of channel estimation based on training sequence by combining it with intra-symbol frequency domain averaging(ISFA)algorithm.It successfully improves the bit error ratio(BER)performance of the system after fiber transmission.2.An enhanced LDPC differential iterative decoding technique is proposed and simulated in single carrier polarization division multiplexing(SC-PDM)coherent optical communication system.Using the high order QAM.The BER performance of the LDPC differential iteration decoding is improved by using the external information.The relationship between ber and the optical signal to noise ratio of the corresponding system is studied by simulation.The simulation results show that the proposed method can effectively overcome the loss caused by the phase ambiguity and improve the BER performance.