Research On Multichannel Signal Equalization Algorithm Under Strong Filtering

With the constant development of the informationized society, the requirement for transmission link capacity of signals is increasing accordingly. To meet the increasing requirement of large-capacity transmission, and break the transmission bottleneck of single channel system link, more and more researches have been done in space division multiplexing (SDM) optical transmission system based on multichannel.With rich mode resources in the multimode fiber and multiple physical transmission channels in the multicore fiber, the combination of multimode optical fiber multiplexing and multicore optical fiber can realize the multiple input/output of the transmission channels, to increase the degree of freedom of the transmission system and breakthrough the capacity limit of the optical communication transmission link. In the multichannel transmission system based on multimode multicore SDM,the multimode optical fiber multiplexing technology can help realize transmission of multiple modes to expand the channel capacity of the link system. Compared with single mode optical fiber, multimode optical fiber has larger nonlinear tolerance and field area to bear information transmission of larger capacity. However, the difference in the transmission speed of different modes in the multimode optical fiber link will lead to mode coupling and dispersion among modes. During the transmission in the multicore optical fiber, signals will be affected by fiber core crosstalk, which leads to lower transmission performance.Therefore, to avoid the influence of system coupling effect on system transmission performance, we need to compensate the link mutilation through effective equalization.In this paper, a few-mode multicore SDM multichannel transmission system mode is established, based on the study of the multiplexing system theory and the coupling in the system transmission link, this paper focuses on the use of strong filtering compression to compress the spectrum of signal, FIR-CMA MIMO equalization Based on mode core combined balance and training sequence equalization based on matrix transformation. The main research works are as follows:(1) Based on the research of Nyquist strong filter signal generation, a strong filtering signal compression method for few-mode multi-core space-division-multiplexing optical transmission system is proposed.Through the strong filtering compression to the optical signal on the sending terminal to compress the spectrum of optical carrier signal, the spectrum bandwidth is close to the filter bandwidth limit. The simulation results show that the strong filtering method proposed in this paper is suitable for the few-mode multi-core multi-channel optical transmission system, which can effectively compress the bandwidth of the signal and improve the spectrum efficiency of the system.(2) Based on the study of random mode coupling, core coupling and dispersion effect in the few-mode multi-core multi-channel optical transmission system, a field coupling model with group delay and mode dispersion is designed, this paper propose the MIMO equalization method of FIR combined with CMA based on mode core combined balance.Compared with the traditional variable step CMA equalization method,this method can reduce the complexity of the channel transmission matrix and has better equalization performance.(3) Based on the analysis of the transmission features of each mode and the matrix transmission coupling model in the few-mode multi-core multi-channel optical transmission system, this paper establishes the optical transmission system which including inter-symbol crosstalk, mode coupling, fiber core crosstalk, and dispersion, and proposing a training sequence equalization method based on matrix transformation. The simulation results show that the equalization in this paper can perform effective compensation to the coupling factors in the optical fiber transmission link to improve the transmission performance of the system link.