中文摘要：

以16-相正交幅度调制（16QAM）为例,分析比较了伽罗华（GF（2^m））域上m=1,2,4时,3种低密度奇偶校验（LDPC）码在16QAM光传输系统中的性能.分析表明,无论在纠错性能还是译码效率方面,4进制LDPC码比16进制LDPC码具有更大优势.为进一步改善高阶调制光传输系统中非二进制低密度奇偶校验（NB-LDPC）码的性能,在16QAM系统下的4进制LDPC码中引入水印位符号.与传统的非二进制LDPC译码方案相比,水印位方案的平均迭代次数显著下降,即引入水印位可以极大地提高NB-LDPC码的译码效率.当误码率BER=10-5时水印位方案可以改善0.1dB的净编码增益.

英文摘要：

Taken 16 Quadrature Amplitude Modulation（16QAM）as an example,the performance of three kinds of LDPC codes over Galois fields（GF（2^m））for m=1,2,4in 16 QAM systems was analyzed.The simulation results show that 4-ary LDPC code,rather than 16-ary LDPC,shows significant advantages in both error correction performance and decoding efficiency.Then in order to further improve the performance of NB-LDPC codes in high-order modulation systems,the watermark symbols are introducted into 4-ary LDPC codes in 16 QAM systems.Compared with traditional non-binary LDPC decoding,the average iteration number of watermark scheme presents a quite obvious decrease,it means that the decoding efficiency can be greatly improved by using watermark scheme.Moreover a further Net Code Gain（NCG）improvement of about 0.1dB can be attained when bit error ratio BER=10-5.