Analysis Of Bit Error Performance In Optical Fiber Communication System Based On Concatenated Coding Modulation

The society has entered the information age, optical fiber communication system is the main tool for conveying information society.With the rapid development of the video business, cloud computing services and mobile broadband services, the demands of people for bandwidth are increasing, and it is need to improve the bandwidth and capacity of optical fiber communication systems.Bandwidth and capacity of optical fiber communication system is mainly affected by factors related to the limitations of attenuation, dispersion, nonlinear effect, etc., which can be soved by modulation technology, FEC technology, RAMAN amplification technology and other means.Based on the research of encoding modulation theory and realization method in optical fiber communication system, this paper focuses on studying the encoding modulation scheme combined with trellis-coded modulation (TCM) technology and low-density parity check code (LDPC)technology, and the Raman amplification technology with optimized gain spectrum.The main innovatative research efforts are summzrized as follows:(1) The technology of trellis coded modulation (TCM) is researche d. The scheme of constellation mapping, subset segmentation modul e, decoding module and overall viterbi decoding module is proposed.The encoding method of 16QAM, 32QAM and TCM-32QAM encod er is designed, the encoding gain and performance are analyzed in simulation.(2) The principle of LDPC coding and decoding is researched, we also simulate the modulation format performance of LDPC-BPSK (with different coding rate) and LDPC-16QAM. Based on the research,we proposed the optimal encoding scheme.(3) Research on the concatenated coded modulation (LDPC-TC M) performance in the optical fiber communication system, the affect of ASE noise, dispersion and polarization mode dispersion to the pe rforamnce of LDPC-TCM scheme in optical fiber communication ar e simulatedly researched. The simulation results shows that the concat enated coded modulation format (LDPC-TCM-32QAM) has superior p erformance.(4) Using a differential gain spectrum optimization algorithm, we proposed a method for optimizing the spectrum of fiber Raman am plifier. The simulation results show that the gain spectrum fluctuatio n of the fiber Raman amplifier is 1.6 dB, and the optimized fiber Raman amplifier can obviously improve the performance of the cas caded trellis coded modulation system.