Research On Probabilistic Shaping And Other Key Techniques For High Order Modulation Optical Communication System Based On Ldpc Code

With the proposal and development of"Internet plus"and"digital China"strategy,the internet traffic will continue to increase sharply in the context of 5G internet of everything and 5G network to be commercialized on a large scale.On the other hand,elastic optical networks are able to optimize network resource allocation well due to their dynamic bandwidth adjustment ability,and they need to achieve a flexible compromise among spectral efficiency,accessible distance and information rate at the physical layer.High order modulation is one of the effective measures to improve communication capacity.In the communication system with limited actual power,it is of great significance to study how to further improve the receiver error performance and reduce its OSNR tolerance requirements in the high-order modulation format.At the same time,how to achieve efficient and reliable elastic transmission of fine particles also has very important research value.In recent years,probabilistic shaping technology has become one of the research hotspots in the field of ultra-high-speed flexible coherent optical transmission due to its advantages in improving the OSNR tolerance and supporting the elastic transmission of fine particles.In this paper,the key issues such as super-100G LDPC-BICM coded modulation technology,probabilistic shaping scheme in high-order QAM system and rate adaptive method of fine particle size are studied and designed.The main research work and results are as follows.1.The structure of the BICM system based on LDPC code was studied,the PM-16QAM-LDPC-BICM system simulation platform and offline experiment platform are established,the performance analysis of the system under different mappings was completed.The simulation results under the condition of 16G Baud PM-16QAM show that the BICM combined with LDPC system using gray mapping has a gain of about 0.6dB compared with the system using natural mapping at the BER level of 1E-5 and the overhead of 20%.At the same time,the net coding gain of about 8.1dB and 7.7dB for the two systems using the mapping is obtained respectively.2.This paper presents a LDPC-based k symbol combination probabilistic shaping scheme(called k-shaped probabilistic shaping).This scheme can not only obtain certain shaping gain,but also realize the flexible tradeoff between redundancy and SNR tolerance performance by combining shaping of different symbols.Simulation results show that in 64QAM modulation format,at the BER level of IE-4,with the cost of sacrificing a certain spectral efficiency.When k=1,the scheme has about 1.73dB tolerance improvement.When k=2,the tolerance of about 0.93dB is increased.When k=3,there is a tolerance increase of up to 0.8dB,and the proposed scheme at this time has a shaping gain of about 0.2dB compared with the pure LDPC coded modulation scheme with the same total over-head.3.A fineness rate adaptive scheme based on probabilistic shaping for high order MQAM modulation was designed.Based on probabilistic shaping,this scheme is able to achieve a fineness flexible compromise of spectral efficiency,information rate and reachable distances in the high-order MQAM modulation format.With the PM-64QAM modulation format,the symbol rate is 28G Baud,this scheme is able to achieve the flexible change of spectral efficiency from 4bit/symbol/pol to 6bit/symbol/pol with a granularity of less than 0.5bit/symbol/pol,and the flexible change of information rate from 224Gbps to 336Gbps with a granularity of less than 28Gbps.Compared with the method of directly changing the modulation format,such as from PM-16QAM to PM-32QAM to PM-64QAM,the rate adaptive scheme based on probabilistic shaping can achieve finer granularity adjustment.4.The PS-PM-MQAM and unshaped PM-MQAM high-speed coherent optical transmission simulation system was built to verify the flexibility of fine-particle adjustment of rate adaptive scheme based on probabilistic shaping.At the same time,the OSNR tolerance performance of the scheme was verified and compared.The results showed that at the BER level of 3.8E-3,at the cost of adding 9.1%redundancy,the PS-PM-64QAM scheme achieved about 3.3dB OSNR tolerance improvement compared with the PM-64QAM scheme.Compared with the PM-256QAM scheme,the PS-PM-256QAM scheme achieved an OSNR tolerance improvement of about 4.1dB at the cost of adding 6.6%redundancy.Compared with PM-16QAM and PM-64QAM schemes with the same spectral efficiency,PS-PM-64QAM and PS-PM-256QAM schemes respectively obtained about 1dB and 1.1 dB OSNR tolerance improvement.