Wavefront Distortion Simulation And Correcting Methods Of Oblique Atmospheric Laser Communication

The geometric growth of information puts forward high requirements on the channel capacity,transmission rate and coverage of communication.Atmospheric laser communication has large channel capacity,fast transmission rate,small communication limitation,high reliability and good confidentiality.And there is no need for frequency licensing when communication.These advantages make the atmospheric laser communication develope rapidly.However,when the laser beam is transmitted in the atmospheric channel,the atmosphere will have a series of effects on it,including atmospheric attenuation,multipath effects caused by multiple scattering,and wavefront distortion of the laser beam caused by atmospheric turbulence.These factors will lead to the signal-to-noise ratio reduces and the bit error rate increases at the receiving end,which restricts the development of atmospheric laser communication.This paper mainly studies the wavefront distortion and distortion correction caused by atmospheric turbulence during laser communication.The specific research contents are as follows:1.For the application of oblique atmospheric laser communication is more extensive,this paper studies,the wavefront distortion of laser beam caused by atmospheric turbulence during the oblique transmitting process is studied.The simulating model of oblique transmitting wavefront distortion is established.The phase screen suitable for simulating slant wave optical transmission is obtained.The Rytov exponential interval layered model is used to stratify the atmospheric turbulence phasescreen simulation interval,and the beam extension is used to calculate the phase screen size corresponding to different heights.Finally,the wavefront distortion of the laser along the entire oblique path is obtained.Comapred with the previous simulation method,the phase difference of the low frequency part is reach to ?/ 2.2.Based on the mutual information theory,the mode method of sensor wavefront correction system is improved.By calculating the mutual information of different modes and wavefront distortion,the mode with large mutual information is preferentially used for wavefront correction,thus to reduce the dimensionality of the reconstruction matrix and improve the wavefront correcting speed without affecting the wavefront correction performance.When the same reconstruction accuracy is achieved,the number of reconstructed modes is reduced to 27.7% of traditional mode method.3.The paper improves the particle swarm optimization algorithm of sensorless wavefront correction system.The metropolis criterion is used to judge whether the current correction state is accepted during the wavefront correction process,so that the particle swarm optimization algorithm has a certain probability to jump out of a local optimum in the correction process.Thus to avoid the premature convergence problem of the particle swarm optimization algorithm in the correction process,and the Strel Ratio convergence value of the improved algorithm in the correction process is increased by32.4%.4.The fractal characteristics of the distorted wavefront in atmospheric laser communication are analyzed,and the fractal characteristics of the laser beam distortion wavefront corresponding to different receiving ends of the atmospheric laser communication system at multiple receiving ends are derived.Based on fractal Brownian motion,the wavefront correction method of atmospheric laser communication system with multiple receiving ends is improved.Without influencing the performance of reception diversity atmospheric laser communication systems,the improved method reduces the correction time by 80%,speeds up the wavefront correction,reduces the use of wavefront detectors,and improves the performance of atmospheric laser communication systems at multiple receiving ends.