Research On Optical Communication Adaptive Digital Equalization Based On LMS Algorithm

Wireless optical communication technology is at the leading edge of communication research,of which equalization technology is one of the most important technologies to improve the error performance of optical communication links.The laser beam transmitted in the near-surface atmospheric turbulence channel is impacted by the multi-path effect,and the signal received by the probe present mutual interference between the symbols before and after,which affect the quality of communication.The channel equalization technology can effectively inhibit the influence of crosstalk between codes to improve the communication quality of laser communication.This thesis studies the application of adaptive digital equalization based on the least mean square error(LMS)algorithm in the near-Earth atmospheric channel.The main contents could be summarized as following:Firstly,the influence of the atmospheric channel on the laser signal is studied in the thesis,including the effects of scattering and turbulence.Secondly,by the MATLAB simulation platform,this thesis mainly analyzes two algorithms based on the least mean square error algorithm which are LMS algorithm and BP(back propagation)neural network algorithm to correct the error performance of the system.Besides,it finds that the LMS algorithm equalizer is superior to the neural network algorithm equalizer in convergence speed and convergence error rate under the condition of decision feedback.Therefore,the LMS algorithm is selected as the hardware implementation algorithm in this study.In addition,the design and study of blind equalization algorithm hardware module based on FPGA(Field-Programmable Gate Array)are fulfilled.The functional simulation is developed through Modelsim which verifies the feasibility and realizability of the program.The thesis establishes the experimental link of atmospheric laser communication to test the BER performance by using equalizer or not in the near-Earth atmosphere channel.The aim of optimizing link error performance is fulfilled through experiment based on adaptive digital equalization technology of LMS algorithm.