Ick-Ho Whang

Recursive Weighted Robust Least Squares Filter for Frequency Estimation

A novel weighted robust least squares estimation approach to the design of recursive frequency estimator for single tone sinusoid is presented. The frequency estimation problem is reformulated as the identification of slowly varying parameters subject to a linear time-varying system which contains the stochastic parametric uncertainties in the measurement matrix. By employing the statistical compensation scheme, the proposed robust frequency estimator successfully eliminates the scale-factor error of nominal weighted least squares frequency estimator. The algorithm shows accurate frequency estimation performance and wide range of robustness in the presence of severe sensor measurement noises. By incorporating the forgetting factor to the estimator, the algorithm can achieve fast convergency and adaptability. Moreover, since it requires small amount of computations compared to the existing estimators, it is attractive for real-time implementation. Theoretical basis and performance evaluation results of this technique are described

Time-to-go estimator for missiles guided by BPNG

Biased proportional navigation guidance (BPNG) law is widely used for missiles to home on the target with the required incidence angle. Nowadays the BPNG law has received great interest for sea skimming anti-ship missile (ASM) littoral operation applications. In this paper, we propose a new time-to-go estimator for sea skimming ASMs guided by the horizontal BPNG law. A BPNG problem is formulated in a simple linearized homing geometry and the solution trajectory is introduced. The length of the BPNG trajectory is approximated based on the solution. The time-to-go estimator is derived by applying the Kalman filter theory to the approximated length. Simulation results show that the proposed estimator can estimate the time-to-go very effectively with small computational load.

An Effective Target Selection Algorithm for ASM(Anti-ship Missile)

In search phase of long-range ASM(anti-ship missile) guidance, a scheme using the selectivity point is used to acquire the correct target ship. The idea is that the ship closest to the selectivity point is chosen as the target. However, since there exist uncertainties in the position of the target ship, the optimal choice of the selectivity point becomes difficult when there are many ships around the target. In this paper, we formulate the optimal selectivity determination problem in the framework of the probability theory. And a target selection algorithm with small computational burden is proposed. Some examples are demonstrated to show its effectiveness

Aerodynamic Derivatives Identification Using a Non-Conservative Robust Kalman Filter

A non-conservative robust Kalman filter (NCRKF) is applied to flight data to identify the aerodynamic derivatives of an unmanned autonomous vehicle (UAV). The NCRKF is formulated using UAV lateral motion data and then compared with results from the conventional Kalman filter (KF) and the recursive least square (RLS) method. A superior performance for the NCRKF is demonstrated by simulation and real flight data. The NCRKF is especially effective in large uncertainties in vehicle modeling and in measuring flight data. Thus, it is expected to be useful in missile and aircraft parameter identification.

Minimum Energy Bang-Bang Control for Vertical Launching Missiles

In order to pass over large uncertainties as quickly as possible in initial launching phase of vertical launching missile systems, bang-bang control strategy is widely used to produce high pitch over maneuver. Once fast pitch down is achieved, conventional PID compensator can be used for fine pitch regulation. The new controller combining open loop control and closed loop control is designed through two steps. Firstly, PI attitude controller combining with conventional rate compensation is designed. Secondly, the optimal switching time of bang-bang control is determined in the sense of minimum energy. Linear and nonlinear 3-DOF simulation results show that the proposed controller is very effective for fast pitch down of vertical launching missiles

Robust Kalman Filtering based on Multiple Hypothesis Techniques

In this paper, a new robust state estimator for linear systems with parametric uncertainties is proposed. The uncertainties affecting the system are regarded as unknown sequences of quantized parametric uncertainties. And then the exact robust estimator is derived by handling the uncertainty parameter sequence hypotheses by means of multiple hypotheses testing (MHT) techniques. However, since the exact filter has to treat ever expanding hypotheses, a suboptimal estimator based on zero scan back concept is proposed. A benchmark example for robust Kalman filtering is demonstrated to compare the performance of the proposed filter with those of an existing robust Kalman filter

A robust horizontal LOS rate estimator for 2-axes gimballed seeker

In this paper, a robust horizontal LOS (line-of-sight) rate estimator for sea skimming anti-ship missile is proposed. A exact LOS rate dynamics model for two-axes gimballed seeker is derived in homing geometry. A new LOS rate estimator is designed by applying a robust Kalman filter to the LOS rate dynamics model. The proposed filter takes into account roll motions and detection gain uncertainties. Simulation results show that the proposed filter performs very well and guarantees the robustness against parameter uncertainties.

Guidance law for formation flight via desired position

A formation flight control scheme under the leader-follower concept is proposed. Desired positions for followers are derived using only the leaders position information. The well-known PNG law is selected to guide the follower to the desired position, and a velocity command is added. We propose the minimum maneuver radius for the leader to prevent deformation by the leaders excessive maneuver. The performance is evaluated via three-dimensional simulations.

Time-to-go estimation filter for anti-ship missile application

In this paper, we propose a new time-to-go estimator for conventional PN guided sea-skimming missiles is proposed. In contrast to the conventional method, our method does not only consider the length of the curved homing trajectory caused by the initial heading error, but also tried to mitigate the influence of the seeker measurement noises. In addition, by adopting a new coordinate system moving together with the target in the estimator design, the effect of target movement on the homing trajectory is efficiently took into account. Simulation results show that the proposed filter can estimate the time-to-go very accurately with small computational load.

Linear recursive target state and time-to-collision estimator for automotive collision warning system

This paper proposes a new linear recursive target state and time-to-collision estimator for the development of the automotive collision warning system. The addressed problem can be cast into the representative nonlinear state estimation under cluttered environment. To prevent the tracking performance degradation due to the inherent nonlinearity between the polar coordinates measurements of the automotive radar and the target state, a practical linear filter design scheme employing the estimated line-of-sight (LOS) Cartesian coordinate system (ELCCS) is proposed. ELCCS is redefined by using a priori LOS estimates in every update period in order to ensure the unbiasedness of the proposed linear tracking filter. Moreover, in order to effectively cope with the cluttered environment and to enhance the target tracking performance, a modified probabilistic data association filter (MPDAF) is newly proposed. Finally, using the most probable closing velocity and range measurements within the validation region, a quasi-optimal linear robust time-to-collision (TTC) estimator is designed. For its linear recursive filter structure, the proposed method is more suitable for the development of the performed and reliable collision warning system. The performance of the proposed scheme is demonstrated by computer simulations.