Research On The Decoding Performance Of Non-binary LDPC Codes In Optical Communication Systems With High-order Modulation

In order to obtain a greater capacity of optical transmission,one of the effective methods is to use high order modulation formats and multiplexing techniques.However an increase in the demand of the system's optical signal to noise ratio(OSNR)is brought by the use of high-order modulation.In optical fiber transmission systems with high-order modulation using forward error correction(FEC)technology is considered as an effective way to improve the error correction performance,maintain the reliability of system communication.Researches have proved that NB-LDPC code has better error correction performance than the binary counterpart with the same bit length.But the decoding complexity of non-binary LDPC codes increases sharply with the increase of the order number.So the key point of the researches of FEC technology in high order modulation optical transmission systems is to find the trade-off between error correction performance and decoding complexity.In this paper,the application of non-binary low density parity check code in high-order modulation optical transmission systems is studied.The detail research contents and conclusions are as follows:(1)Firstly,the basic principle of binary LDPC codes and non-binary LDPC codes are studied,including the construction of the check matrix,the algorithms of encoding and decoding,and the error correction performance.The error correction performance of binary LDPC and 4-ary LDPC codes in QPSK system is compared with MATLAB simulations.The results show that the error correction performance of the 4-ary LDPC codes is better than that of binary codes.(2)A 128Gb/s optical transmission simulation system with 16QAM high order modulation is built,and the performance of binary,4-ary and 16-ary LDPC codes are compared in this system.Our results demonstrate that,in 16QAM optical systems 16-ary LDPC codes produce a BER performance degradation in NCG of about 0.5 dB relative to 4-ary LDPC codes.Moreover,the average iteration number of the 4-ary LDPC codes is the least.It is indicated that the 4-ary LDPC code is more suitable for the FEC scheme of 16QAM optical transmission system.(3)The performance of the non-binary LDPC scheme based on watermark symbols in optical systems with high-order modulation is studied.The error correcting performance and decoding efficiency of the non-binary watermark scheme and the traditional non binary scheme are compared.The results show that:compared with the traditional non binary LDPC scheme,the non-binary scheme based on watermark symbols can further reduce the average number of iterations,which makes the decoding efficiency effectively improved.Moreover,when the BER is 10'5,the watermark scheme can also attain a 0.1dB improvement of the net coding gain(NCG).In a word,our studies focus on the performance of non-binary LDPC codes in optical transmission systems with high-order modulation.The performance of different LDPC codes in 16QAM system is analyzed and compared.Then,we introduce the watermark symbols into the non-binary LDPC codes and explore the performance of the watermark scheme in the optical system with high-order modulation.The results show that the non-binary watermark scheme presents outstanding advantages both in improving the decoding efficiency and the error correction performance,which is significant for the researches of FEC technology in the optical transmission system with high-order modulation.