Research On Demultiplexing Technology Based On Lattice Reduction For MDL-injured Mode Division Multiplexing System

In recent years,with the rapid development of the communications industry,5G technology,the Internet of Things,cloud computing,big data and other bandwidth-consuming informational services have continuously emerged,and global network bandwidth demand has grown rapidly.However,due to the inherent non-linear effect of single-mode fiber(SMF),its transmission capacity has approached the Shannon limit.The mode division multiplexing(MDM)system based on the few-mode fiber(FMF)uses multiple orthogonal modes as the carrier of the signal to realize the simultaneous transmission of multiple signals,thereby increasing the capacity of the communication system multiply.However,compared with SMF,FMF has unique damages such as mode-dependent loss(MDL),mode coupling(MC),and differential mode group delay(DMGD).These damages will destroy the orthogonality between modes,resulting in the channel crosstalk and intersymbol interference of signals during transmission.which affects the communication quality of the MDM system.For the effects of impairments such as DMGD and MC on the signal,we can use the signal equalization algorithm in the MIMO system to effectively compensate them.However,as the transmission distance increases,the MDL will continue to accumulate.When the MDL accumulate to a certain degree,the orthogonality of the channel transmission matrix of the MDM system will be severely damaged,which will cause the performance of the traditional equalization algorithm drops sharply,even does not work.Therefore,it is the focus of this paper to study a demultiplexing method for a MDL-injured MDM system.The specific work of this paper is as follows:First,the basic concept and structure of the FMF are introduced in detail.The mode characteristics of the FMF are analyzed mathematically,and the orthogonality between the spatial modes is verified.This paper systematically studies the causes of the three types of damages,such as MDL,MC,and DMGD,and their damage mechanism in the FMF transmission link.Based on that,and combined with the matrix transmission model,a mathematical model of a FMF transmission link is established.Secondly,the demultiplexing performance of linear detection,interference cancellation detection,sphere decoding detection,maximum likelihood detection,andimproved reduce search-maximum likelihood detection for MDM systems are studied.The demultiplexing performance of the above algorithms are simulated in the construction of a 6 × 6 MDM simulation system,and combined with the calculation complexity,the feasibility of their application in the actual MDM system is analyzed.Finally,the paper creatively proposes to use the lattice reduction technique for the demultiplexing of the MDL-injured MDM system.The principles of lattice reduction and the demultiplexing algorithm based on lattice reduction are discussed in detail.The 6 × 6 MDM simulation system is used to verify the demultiplexing performance of the algorithm.The condition number of the channel matrix before and after the Lattice reduction is compared,and it is proved that the Lattice reduction technology can effectively improve the orthogonality of the channel matrix under strong coupling conditions.In the case of different MDL,the performance of the demultiplexing algorithm based on lattice reduction is studied,and it is verified that the algorithm can successfully achieve the demultiplexing of the MDL-injured MDM system and the computational complexity is moderate.So it is of great significance for the realization of long-distance,large-capacity optical fiber communication transmission.