Research On Line-of-sight Pointing Technology Of Spatial Optical Communication System

Due to the point-to-point communication mode,the spatial optical communication system needs to complete the three processes of pointing,acquiring and tracking(PAT)of the communication line-of-sight(LOS)before the communication starts.In the PAT system,the first step is the initial LOS pointing,so the accuracy of the initial LOS pointing directly determines whether the communication system can be acquired successfully.The pointing is completely an open-loop process,and the size of the pointing accuracy determines the size of the field of acquisition uncertainty.When assembling and operating the optical communication terminals,the position errors(longitude,latitude,elevation),attitude angles errors(pitch angle,yaw angle,roll angle),mounting angle alignment errors and dynamic lag errors between different coordinate systems are usually inevitable,which lead to the pointing errors.In general,the size of the field of uncertainty(FOU)for spaceborne optical communication system is 4?6 mrad,and that for airborne optical communication system is 10 mrad.Therefore,how to improve the LOS pointing accuracy and reduce the size of the FOU is one of the key technologies of the spatial optical communication system.This paper takes the LOS pointing system of the dynamic laser communication as the research background.Firstly,the working principles of the laser communication system and the PAT subsystem are introduced,and the LOS pointing principle of the communication system is introduced in detail.On the Basis of the real-time updated position and attitude information of the global positioning system(GPS)and inertial navigation system(INS),a coordinate transformation matrix is used to calculate the LOS pointing angle.Secondly,the factors affecting the LOS pointing accuracy error are analyzed and the two schemes are proposed to reduce the initial LOS pointing errors.One solution is a LOS calibration method to reduce the pointing errors of the system.The CCD camera is used to calibrate the pointing angles to correct the installation errors of the instruments and the measurement errors of the angles,thereby reducing the system errors.The other is to add the information processing methods and techniques such as the least squares,Bayesian estimation,Kalman filtering,and particle filtering into the initial LOS pointing system.This method deals with sensor errors and dynamic lag errors,thereby smoothing the data fluctuation and reducing the dynamic lag.The simulation and experimental results show that the position,attitude angle,and other data fluctuations output by the combined GPS/INS systems can be smoothed effectively by adding a classical Kalman filtering,particle filtering,and extended Kalman filtering information processing methods to the LOS pointing system.And the prediction function of the filter can reduce the influence of dynamic lag.The proposed approach improves the accuracy of the LOS pointing,reduces the size of the FOU,and provides reference and guidance for the design of space optical communication systems.