Research On Blind Channel Equalization In High Bit-rate Wireless Optical Communication System

Atmospheric laser communication has the advantages of high bandwidth and strong anti-electromagnetic interference ability. Atmospheric laser communication is at the cutting edge of communication research.Atmospheric turbulance is one of the main factors which have influence on the performance of a laser communication system. During the transmission of laser, the phase and amplitude of laser will change by the reason of channel change. In this condition, channel equalization can be used to slow down and suppress the ISI caused by multipath effects and other factors. Thus communication performance can be improved by channel equalization.In this paper, based on atmospheric channel, a blind equalization is researched in the light intensity modulation condition with baseband bit rate 200Mbps.The main work contain:1. In this paper, the signal transmission model of atmospheric laser communication is analyzed and in this process the influence of atmospheric channel on laser transmission is analyzed emphatically. Then the mathematical model and realization method of equalization are obtained. At the same time, the design indexes of the equalization is gave in the analysis.2. Analyze and research the blind equalization algorithms. In this process focus on the Godard algorithm and the blind equalization algorithms based on higher order statistics. Then, according to the characteristics between different algorithms, the CMA+DD algorithm has selected in this paper. After the algorithm analysis, the solution to the algorithm is analyzed.3. The hardware of the selected blind equalization algorithm is completed by use of****'s **** FPGA chip. In the design process focus on the signal clock extraction and adaptive filter design. Finally, the CMA + DD algorithm is implemented in the FPGA chip.4. The performance of the blind equalization algorithm is tested in near-Earth atmospheric turbulence conditions. The signal diversity technique in atmospheric laser communication system is researched at the same time.