Application Of Low-density Parity-check Code In Phase-estimated Optical Coherent Receiver

Recently, high speed optical communication develops rapidly with the increase of Internetapplication and the popularization of broadband access network. However the transmissionperformance of optical fiber reduces obviously due to various impairments in channel when in highbaud speed. Thus, advanced technologies in detection, coding and signal processing should beexploited to overcome the impairments introduced by the optical channel.Firstly, we study the optical coherent detection technology and analysis the model of coherentreceiver with two different phase estimation algorithms: M-th Power phase estimation and DecisionAided-Maximum Likelihood (DA-ML) phase estimation. The performance of two phase estimationschemes is compared, and the conclusion is that the BER performance of DA-ML schemeoutperforms that of M-th Power slightly when Forward Error Coding (FEC) is not added. This isdue to the fact that M-th Power requires nonlinear operations and it induced phase ambiguous.Secondly, this thesis studies FEC technology and discusses the application of Low-DensityParity-Check Codes (LDPC) in optical communication system. Moreover, we analysis the formationof LDPC code that adapts to optical communication system with high speed and high efficiency andwe further discuss the algorithm of LDPC decoding. To achieve the soft input and soft outputdecoding in decoder, we study the soft iterative decoding algorithm which is based on softdemodulation and it obtains0.3dB gain compared to that without soft demodulation.Finally, the performance of LDPC decoding in the presence of laser phase noise is analyzed.The demodulation scheme which combines the M-th Power phase estimation algorithm and the softiterative decoding algorithm is also proposed. Simulations are conducted to analysis our proposedscheme and the conditional scheme such as M-th Power and DA-ML scheme. We finally draw theconclusion that our new demodulation scheme can achieve both higher accuracy in phase estimationand lower complexity in decoding. Thus this scheme can achieve high decoding performance tooptimize performance of the receiver reflecting its high practical value.