Research Of Adaptive Equalization In Atmosphere Communication System

Atmosphere Laser Communication (ALC) refers to the technology of transmitting voice, data and graphics using laser bean. Because of its advantage of narrow transmission bean, small antenna size, broad information capability and high performance to price, it impressed many people in communication area. So it has good application foreground in resolve of "The Last Kilometer Problem" and emergence communicatioa The transmission of laser in atmosphere was affected by kinds of factors in atmosphere channel. It brought signal attenuation and inter-symbol interferences. It leaded the addition of bit error rate. This paper solved the problem through adaptive equalization technique.In the first part of thesis, atmosphere laser communication system was introduced in brief, and the research actuality in atmosphere laser communication about research institution in nation and abroad was analyzed. Then according to the characteristic of atmosphere laser communication, the scheme about research of adaptive equalization in atmosphere laser communication system was advanced.This paper studied the least mean square (LMS) algorithm, validated the contradiction between the convergence speed and the overmeasure mean square error (MSE). Thorough analysis and study about variable step size LMS algorithm were done to solve the contradiction being aroused by fixed step size of LMS algorithm. Variable step size LMS algorithm contained three types: 1, step size was based on error signal; 2, step size was based on estimation about cross correlation of error signal and filter input vector; 3, step size was based on estimation about auto correlation of error signal Analysis, simulation and comparison about representative algorithms in all types were done.The new variable step size LMS algorithms were advanced. New algorithm had more rapidly convergence speed, less steady state mean square error, and more rapidly track speed. This algorithm was prone to carry out real time signal processing because of simple operation. Study on the dual-mode blind equalization algorithm, combining the conventional blind equalization algorithm with the decision direction, aiming at the disadvantage of excessive overmeasure mean square error about blind equalization algorithm. The feasibility of the dual-mode blind equalization algorithm was validated through the simulation in the atmosphere laser channel.