Research On Fine Tracking Control System For Mobile Platform Wireless Laser Communication

In recent years space optical communication (Free space called communication, FSO) showed extensive and far-reaching influence both in the field of military, science and technology and civilian. Mobile platform optical communication is mainly focus on the mobile platform space optical communication technology, including the vehicles, ships, aircraft and so on, and it is one of the main means for people to explore outer space, collect vast amounts of real-time information, dealing with sudden disasters and other emergencies effectively. However, the high precision acquisition, pointing and tracking (Acquisition, pointing and tracking, APT) is the first step for FSO. Because mobile platform space optical communication terminals moving fast, attitude change quickly and affected by their vibration, it is more difficult for achieving high precision pointing and tracking than others. Therefore, it is important to research on mobile platform space optical communication. As a project supported by the national defense, the mobile platform space optical communication research mainly solve the problem of the high precision tracking technology of optical communication terminal. In this paper, we mainly focus on the theoretical research and system development of high precision beam control and tracking technology for mobile platform space optical communication.First, this paper introduced the basic concept of space optical communication and mobile platform space optical communication and its characteristics and key technologies. And its development trends both at home and abroad were introduced in detail. Focus on the main research achievements in space optical communication of WuHan university laser communication lab. Summarized the APT technology of fine tracking in space optical communication. It's includes the position detector, precision beam deflection mechanism, fine tracking spot positioning technology and precision tracking servo control technology of beacon light, etc.Second, the characteristics of the mobile terminal platform atmospheric signal channel is analized in this paper. Introduced the basic theory of atmospheric turbulence, analized the effects of flashing, drift, arrival Angle fluctuation and the receiving light power ups and downs, influenced by the turbulence atmospheric channel. Mainly analyzed the arrival Angle fluctuation and the receiving optical power ups and downs of receiving power of the mobile platform space optical communication.Again, based on the parameters of least squares hierarchical method the tracking system transfer function was identified and The identification precision of model is high. The experimental results show that amplitude-frequency response accuracy within 800 rad/s is less than 0.3 dB and phase-frequency accuracy is less than 2.1°. Beacon light characteristics are analyzed in detail, and discovered the fine tracking beacon light spot gray level distribution law in a small area, puts forward a kind of adaptive threshold segmentation method for mobile platform of space optical communication, and the method better solved the problem of the real-time and the huge amount of data processing. A feedforward control algorithm and fuzzy adaptive control algorithm based on kalman filter were designed for mobile platform system. All the control algorithm were optimized in the control effect and the system resource usage, improve the overall system performance.Then, according to the requirement of the system, a miniaturization, high stability precision tracking control system. A miniaturized, high stability precision tracking control system was designed based on igh frame frequency CMOS camera for mobile platform optical communication system. Analyzed the advantage of CMOS camera used as location detector for fine tracki ng system, completed the design and manufacture of software and hardware. System can realize frame frequency of 8800 hz image acquisition, transmission and real-time image processing, spot centroid calculation and servo control, etc. Analyzed the impact of CMOS camera noise, frame rate and light spot centroid algorithm on the tracking accuracy of fine tracking system, when camera frame rate increased from 2200 Hz to 8800 Hz tracking standard deviation reduced from 1.8 to 0.5 pixels; field spot centroid algorithm deviation is bigger than Gaussian-distributed beam spot 8.34-0.71 pixels.Finally, set up a experiment platform for mobile platform space optical communication APT system, carried out indoor and outdoor 3.4 km performance verification experiment. Two experiments were carried out respectively, one is the test of CMOS camera tracking accuracy, the other is the tracking bandwidth for fine tracking system. Outdoor field experiment of 3.4km turbulenc channel was carried out and the simulation tracking experiment and platform vibration suppression experiment to varify the availability of the system. All the experiments show that the fine tracking system has strong rejection effect on airborne platform vibration, the tracking accuracy is about 3? rad. The receiving signal power can be improved 4-5.9 dB in simulated aircraft to ground communication experiment. The fine tracking system has the characteristics of flexibility and high accuracy. Verification experiments made us fully understood the principle of the the atmospheric channel and terminal vibration characteristics and had made important preparation for future aircraft test.