Compared to the mainstream microwave communication methods, laser communication offers advantages such as high data rate, large capacity, compact size, low power consumption, and strong confidentiality. As satellite laser communication becomes increasingly practical, laser communication networking has emerged as a crucial research direction and foundational technology for future space-based communication. However, the narrow beam divergence of laser limits them to point-to-point communication, making them unsuitable for the wide coverage typically achieved with radio frequency communication. Achieving multi-beam, high-precision control under complex space conditions is one of the key challenges in inter-satellite laser communication networking. Currently, most laser communication tracking servo systems utilize the proportional-integral-derivative (PID) control algorithm. While there have been improvements to traditional control algorithms and applications of modern control methods, issues such as low control accuracy and application difficulty remain. In this study, we propose an improved active disturbance rejection control (ADRC) algorithm designed to improve control accuracy in laser communication networking.

The control strategy for a one-to-many laser communication terminal is studied. The structure and control system of a one-to-many coarse tracking optical antenna are analyzed. Based on ARDC principles, a model-assisted extended state observer combined with a Kalman filter is developed to improve disturbance estimation. The controller is designed using the desired frequency response method. Simulations are conducted, followed by experiments on an indoor platform.

In linear ADRC, the system is treated as a simple integrator chain when designing the control law. By incorporating known model information into the design of the extended state observer, we overcome the performance limitations of traditional observers. Thermal noise and ambient light can affect the positioning accuracy of the four-quadrant detector. While code division multiple access (CDMA) techniques can reduce background light interference, they cannot fully eliminate it. Therefore, a Kalman filter is introduced before the extended state observer to reduce overall measurement error, with its output serving as input for the observer. The controller is designed using the desired frequency correction method, which is known for stable performance and ease of implementation. Modeling errors and external disturbances are compensated for by the improved extended state observer, bringing the actual system model closer to the ideal model. Simulation results indicate that the Kalman filter effectively suppresses high-frequency noise. Under traditional PID control, the peak tracking residual is 1.71°, with a root mean square (RMS) of 0.95°. For linear ADRC control, the peak is 1.21° and the RMS is 0.75°. With the improved linear ADRC, the peak tracking residual is reduced to 0.92°, with an RMS of 0.38°, significantly outperforming both PID and linear ADRC controls. In the experiments, the error peak for the primary mirror under PID control is 171.2 μrad, with an RMS of 69.66 μrad. With the improved ADRC, the error peak is reduced to 134.1 μrad, with an RMS of 45.50 μrad. For the slave mirror linkage control, the error peak under PID control is 33.81 μrad, with an RMS of 11.49 μrad, while the improved ADRC reduces these values to 20.22 and 6.81 μrad, respectively. These results show that the control accuracy for the primary mirror improved by 34.6% compared to PID control, and for the slave mirror, by 40%. The consistency between the simulation and experimental results verifies the effectiveness of the proposed control algorithm.

To enhance disturbance estimation, known model information is incorporated into the extended state observer. To mitigate the effect of noise from the four-quadrant detector, a Kalman filter is applied before the observer’s input. In addition, loop bandwidth compensations are integrated into the controller design. Experimental results demonstrate that the tracking accuracy for the dual spot is better than 50 μrad, with a 34% improvement over traditional algorithms. This confirms the feasibility of applying the improved ADRC to multi-beacon tracking scenarios, highlighting its advantages over traditional control methods and its potential to support laser communication applications in inter-satellite networking.