Research On Modulation Format Identification Technology Base On Clustering Algorithm In Optical Fiber Communication System

The development of new technologies such as 5G mobile communication technology,artificial intelligence,and autonomous driving,various emerging Internet applications(E.g HD video,large data centers,and the Internet of Things,etc.)are also developing rapidly.As the infrastructure of global communication network,modern optical fiber communication system is facing unprecedented opportunities and challenges.To provide real-time and flexible services for different users,the next-generation optical network is bound to develop towards elastic,heterogeneous,low-cost,and reconfigurable elastic optical network(EON),which requires continuous upgrading of network support.Simultaneously,as new high-speed services,the normal operation of traditional services is guaranteed.Through intelligent transceivers,EON can flexibly control parameters such as modulation formats and baud rate,thereby maximizing bandwidth resource utilization.In the complex next-generation optical network,how to effectively manage the network’s available resources is a huge challenge.To ensure the quality of communication links and signals,a reliable real-time optical communication parameter monitoring system is essential.In this system,the optical performance monitoring(OPM)module obtains the optical communication physical link information reflecting the quality and performance of the optical signal in real-time,perceives the communication damage or locates the fault,and then realizes the effective management of resources.To increase the capacity of optical communication systems,higherorder modulation techniques are more and more widely used in current high-speed optical communication systems.This enables a variety of modulation formats to coexist in optical communication networks.To ensure that the receiving end can flexibly adapt to this situation,how to realize automatic identification of the modulation formats used in the communication system is a new problem raised in the new generation optical network.The solution to this problem is the key to realizing automatic regulation of the receiving end in the optical network.In addition,the flexible network environment in the new cognitive optical network(CON)makes this problem more obvious.On the one hand,the transmitting end needs to determine the signal modulation format according to the quality of the optical fiber transmission link and user transmission requirements,and flexibly configure the bandwidth resources,which is a necessary condition to ensure the stable operation of the OPM.On the other hand,some signal damage compensation algorithm in digital signal processing(DSP)needs to determine the signal modulation formats to accurately recover and decode the received signal.In summary,the research on Modulation Format Identification(MFI)technology in optical fiber communication system is a critical technology research to realize the signal demodulation and decoding scheme of the intelligent receiving end,and it is also an important guarantee for the reliable transmission of the next-generation high-speed optical fiber communication backbone network.Aiming at the problem of modulation format identification in optical fiber communication systems,this paper studies different modulation format identification schemes and algorithms and channel impairment equalization algorithms.A key-block-based adaptive modulation format identification scheme is presented,and a related algorithm is given.The main research contents of this paper are as follows:(1)In the 28 Gbaud polarization domain multiplexing(PDM)optical fiber communication system,study the transmission signals of 4 common modulation formats(4QAM,16QAM,32QAM,and 64QAM)under the action of various system impairments.The representation and distribution characteristics of the graph space.(2)Contrary to the fact that the signal is easily affected by channel damage after transmission through the optical fiber,this paper use modulation format independent phase noise and frequency offset precompensation scheme and constructs the key blocks of different modulation format signals as the MFI features.The identification accuracy of MFI and the tolerance to physical damages such as ASE and residual chromatic dispersion are improved,and the complexity of the system is reduced.(3)Research the improvement scheme of the expected number of clusters and the selection strategy of the initial cluster center of the clustering algorithm,and design a clustering evaluation function based on the Silhouette coefficient of the clustering effectiveness index.The result of MFI can reach the global optimum and have strong interpretability.(4)The performance of the proposed MFI scheme based on clustering adaptation is verified by 10,400 numerical simulations in the 28 Gbaud PDM communication system.The results show that when the OSNR values of PDM-4QAM,PDM-16QAM,PDM-32QAM,and PDM-64QAM signals are respectively lower than the 7%FEC threshold of the corresponding format,the MFI scheme can achieve 100%identification accuracy.In addition,the data show that this scheme has high residual dispersion tolerance and low complexity.(5)To further verify the reliability and applicability of our MFI scheme,a 20 Gbaud PDM long-distance optical fiber communication experimental system was built,and the PDM-4QAM,PDM-16QAM,and PDM-64QAM signals were transmitted over long distances of 2000km,1000km,and 400km respectively.After the test,the results show that proposed MFI scheme has a high identify accuracy,and has a good tolerance for nonlinear damage,which is suitable for real optical fiber communication systems.