Point ahead angle prediction based on Kalman filtering of optical axis pointing angle in satellite laser communication
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Point ahead angle prediction based on Kalman filtering of optical axis pointing angle in satellite laser communication Zhang Furui1 · Ruan Ping2 · Han Junfeng2 Received: 15 March 2020 / Accepted: 22 July 2020 © The Optical Society of Japan 2020
Abstract Point ahead angle (PAA) prediction is important in space laser communication, but the existing methods have low accuracy and complicated calculation processes. In this paper, a new PAA prediction method is proposed based on Kalman filtering of the optical axis pointing trajectory. The proposed method uses the high precision of fine tracking to improve the accuracy of predictive filtering. Taking ground-satellite laser communication as the research background, the beam transmission process in a typical acquisition, pointing, and tracking (APT) system is derived, then the Kalman filter model is established, and a simulation of the model is performed. The results show that the PAA can be predicted accurately and the error of the PAA can be reduced effectively the maximum prediction error is 3.8 μrad only, and the method does not need to take the complex satellite perturbations into consideration. The proposed approach improves the accuracy of PAA prediction and contributes to the design of space laser communication systems. Keywords Point ahead angle · APT system · Kalman predictive filtering · Space laser communication
1 Introduction Due to its advantages, including higher capacity communication rate, stronger anti-interference ability, cost-effectiveness, and longer link distance achieved with terminals that have lower size, weight, and power, satellite optical communication (SOC) has become a promising scheme and a technology complementary to radio frequency (RF) communication [1–4]. Therefore, the technique has been widely studied around the world. Because the communication laser beam width is very narrow (dozens of microradians), an acquisition, pointing, and tracking (APT) system, in which a composite of coarse tracking and fine tracking is adopted, is usually used to control the beam pointing direction to avoid losing target [5–7]. Additionally, because the link distance in SOC is very long (hundreds to tens of thousands of kilometers), it takes time for light to travel the path, and there will be an angle difference between the optical axes * Zhang Furui [email protected] 1
College of Optoelectronic Engineering, Xi’an Technological University, Xi’an 710021, China
Xi’an Institute of Optics and Precision Mechanics (XIOPM), Chinese Academy of Sciences (CAS), Xi’an 710119, China
2
of the two terminals due to relative angular motion, which is called the point ahead angle (PAA). The precision of the PAA can affect the link stability and communication bit error rate; therefore, it is necessary to improve the precision of the PAA. In the previous studies, many scientists have determined the PAA value range under different satellite orbit attitudes [8, 9]. In their models, the formula θp = 2·v/c [10] is always used to calculate the PAA, wher
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