Study On The Spot Locating And Tracking Algorithm Of Beacon In Satellite Laser Communications

Compared with microwave communications,satellite laser communications has a lot of advantages,which is the popular research orientation currently.In the communication process,the aiming,capturing,and tracking of laser beams are the focus and difficulty of research.During the establishment of the laser communication link,first thing needs to do is to use the beacon light to aim at the receiving terminal and determine the direction of the beacon light.The key to determining the direction is to accurately locate the center of the imaging spot on the receiving terminal.Due to the influence of atmospheric turbulence during the optical transmission of free optical communication,the wavefront distortion of the beam will cause the imaging spot light intensity distribution at the receiving terminal to be uneven or even broken,which brings difficulties to compute the spot center precisely.This paper analyzes how to determine the azimuth angle of the beacon light through the center of the spot firstly,and then analyzes the basic theory of atmospheric turbulence.The atmospheric phase screen is produced by Zernike polynomial,and is applied to imitate numerically the spot when it is affected by atmospheric turbulence of different intensities.The numerical simulation shows that because of meteoric turbulence,the laser wavefront is distorted,so the beacon spot collected at the receiving terminal will have uneven graycale intensity distribution,drift and dispersion,and fragmentation.Secondly,in addition to atmospheric turbulence,the noise of the spot image will also affect the positioning accuracy of the spot center.Therefore,this paper analyzes the main noise sources in the process of spot imaging.This paper ameliorates a denoising algorithm based on wavelet to remove the spot noise.The simulations verify that by contrast with the traditional algorithm,the ameliorated algorithm performs better.And then the centroid method is used to determine the center of the spot based on the low-frequency wavelet coefficients.Compared with the direct use of the spot image to determine the center of the spot,the accuracy of the spot based on the low-frequency wavelet coefficient is higher.Finally,in order to improve the alignment speed,it is necessary to track and predict the beacon light.This paper comes up with a new prediction algorithm to predict the position of the beacon.Compared with the traditional least squares method,the new predict method is obviously better than the least square method when used to predict the mid-to-high frequency vibration.