Time filter

Source Type

Wang D.,Communication University of China | Fan J.,Communication University of China | Li Y.,China Xian Satellite Control Center
Journal of Convergence Information Technology | Year: 2012

LFM signals are widely used in the fields of radar and communication etc., which make signals detection and parameters estimation a very important technology in multicomponent LFM signals. To solve the problems of error detection caused by the cross-terms in WVD-Hough methods and other modified WVD distribution methods, and low parameter estimation precision due to poor timefrequency concentration in S-Hough transform, this paper proposed a detection and parameter estimation algorithm of multicomponent LFM signals based on reassigned generalized S-transform and Hough transform. Firstly calculate the time-frequency distribution of multicomponent LFM signals by generalized S-transform. Secondly reassign the S-transform time-frequency distribution to improve the time-frequency concentration property. Finally implement signal detection and parameter estimation by Hough transform to the reassigned S-transform TFD. The simulation results show that this algorithm has good performance in detecting multicomponent LFM signals and estimating the parameters in low SNR case.

Wang D.,Communication University of China | Fan J.,Communication University of China | Li Y.,China Xian Satellite Control Center
International Journal of Digital Content Technology and its Applications | Year: 2012

The Nonlinear Frequency Modulation (NLFM) signals have been gradually used in new radar systems, however its instantaneous frequency (IF) estimation is still a difficult problem. This paper introduces the generalized S-transform to NLFM signals processing fields and proposes a new IF estimation algorithm of NLFM signals in low SNR based on generalized S-transform. Firstly, the timefrequency distribution (TFD) of NLFM signals in low SNR is got by generalized S-transform. Secondly, a time-frequency (TF) filtering processing is executed to the TFD of NLFM signals and the noise is restrained. Finally the TFD spectrum ridges are extracted as IF curves estimation from the filtered TFD of NLFM signals. Simulation results demonstrate that the IF estimation algorithm proposed in this paper has better performances in IF estimating of NLFM signal in low SNR than other existing algorithms.

Cao L.,China Xian Satellite Control Center | Li H.,China Xian Satellite Control Center
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2016

For the attitude estimation problem, the quaternion is preferred to describe the rotation of spacecraft, which obeys a unit-norm constraint. However, this constraint is not considered in the most of the traditional estimation algorithms. This work will develop a new estimator named norm-constrained predictive filter to solve this problem based on the predictive filter frame. The optimization theory of Lagrange multiplier is adopted by minimizing a constrained cost function to improve the traditional predictive filter. In addition, the obtained estimator is further analyzed and applied to the spacecraft attitude estimation problem by numerical simulations. © Institution of Mechanical Engineers.

Cao L.,China Xian Satellite Control Center | Li H.,China Xian Satellite Control Center
Acta Astronautica | Year: 2016

For the satellite attitude estimation problem, the serious model errors always exist and hider the estimation performance of the Attitude Determination and Control System (ACDS), especially for a small satellite with low precision sensors. To deal with this problem, a new algorithm for the attitude estimation, referred to as the unscented predictive variable structure filter (UPVSF) is presented. This strategy is proposed based on the variable structure control concept and unscented transform (UT) sampling method. It can be implemented in real time with an ability to estimate the model errors on-line, in order to improve the state estimation precision. In addition, the model errors in this filter are not restricted only to the Gaussian noises; therefore, it has the advantages to deal with the various kinds of model errors or noises. It is anticipated that the UT sampling strategy can further enhance the robustness and accuracy of the novel UPVSF. Numerical simulations show that the proposed UPVSF is more effective and robustness in dealing with the model errors and low precision sensors compared with the traditional unscented Kalman filter (UKF). © 2016 IAA

Cao L.,China Xian Satellite Control Center | Chen X.,National University of Defense Technology
Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering | Year: 2015

Under the existence of system uncertainties and external disturbances, complete synchronization of chaotic systems is achieved by introducing a novel input-output linearization minimum sliding mode error feedback control with high control precision, which is based on the input-output linearization method and sliding mode control. In the literature, the magnitudes of bounded nonlinear dynamics of synchronous error system were required in the designed sliding mode controller. In this study, this article proposed a new approach to estimate the various uncertainties and disturbances on the basis of chaotic system. To facilitate the analysis, the concept of equivalent control error is introduced, which is the key to the utilization of input-output linearization minimum sliding mode error feedback control. A cost function is formulated on the basis of the principle of minimum sliding mode covariance constraint; then, the equivalent control error is estimated and fed back to the conventional sliding mode. It is shown that the sliding mode after the input-output linearization minimum sliding mode error feedback control will approximate to the ideal sliding mode, resulting in improved control performance and quality. Finally, the chaotic gyro system and chaotic FitzHugh-Nagumo neurons system have been employed to verify the proposed controller. Sufficient conditions to guarantee stable synchronization are given and the numerical simulations of complete synchronization of the two chaotic systems are performed to verify the effectiveness of the presented schemes. © 2015 Institution of Mechanical Engineers.

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