Journal of Professor & SPaC member

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Last Updated : 03/2016
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  • Polynomials-based integral inequality for stability analysis of linear systems with time-varying delays

    Seok Young Lee, Won Il Lee, PooGyeon Park

    Journal of the Franklin Institute


  • New stability analysis for discrete time-delay systems via auxiliary-function-based summation inequalities

    PooGyeon Park, Seok Young Lee, Won Il Lee

    Journal of the Franklin Institute

    AbstractFor the stability analysis of discrete time-delay systems, Jensen inequality has been widely used as the method supporting inequalities for summation quadratic functions. It not only requires a smaller number of decision variables than other approaches but also achieves identical or comparable performance behavior. Based on the analysis for the conservatism of Jensen inequality, however, this paper suggests a new summation inequality say an auxiliary-function-based summation inequality. It is verified that the proposed inequality is a generalized form of the novel summation inequality reported recently. Also, an application to stability analysis for discrete time-delay systems is provided.

  • Improved H∞ state-feedback control for continuous-time Markovian jump fuzzy systems with incomplete knowledge of transition probabilities

    Nam Kyu Kwon, Bum Yong Park, PooGyeon Park, In Seok Park

    Journal of the Franklin Institute

    AbstractThis paper proposes the improved H∞ state-feedback control for Markovian jump fuzzy systems (MJFSs) with incomplete knowledge of transition probabilities. From the fundamental first-order properties of the transition rates, two second-order properties are introduced without information on the lower and upper bounds of the transition rates, differently from other approaches in the literature. Based on these properties, this paper uses all possible slack variables into the relaxation process which contributes to reduce the conservatism. Finally, two numerical examples are provided to illustrate the effectiveness of the proposed method.

  • A Variable Step-Size Normalized Subband Adaptive Filter with a Step-Size Scaler against Impulsive Measurement Noise

    Junwoong Hur, Insun Song, PooGyeon Park

    IEEE Transactions on Circuits and Systems II: Express Briefs

    AbstractThis letter introduces a variable step-size (VSS) normalized subband adaptive filter (NSAF) using a step-size scaler to improve the robustness against impulsive measurement noise. When impulsive measurement noise appears, the step size of the proposed VSS NSAF is scaled down by the step-size scaler, which is suitable for application in the NSAF. This removes a possibility of updating weight estimates based on defective information of the subband output errors due to impulsive measurement noise. In the proposed VSS NSAF, the equations for updating the step size are constructed by interpreting the behavior of the mean square deviation (MSD) of the conventional NSAF and applying the step-size scaler. The step-size scaler utilizes the sum of the subband output errors, which can be influenced by impulsive measurement noise. Simulations using the proposed VSS NSAF show an excellent transient and steady-state behavior with colored input in impulsive-noise environments.

  • A combined first-and second-order reciprocal convexity approach for stability analysis of systems with interval time-varying delays

    Won Il Lee, Seok Young Lee, PooGyeon Park

    Journal of the Franklin Institute

    AbstractFor the interval time-varying delay systems, Jensen inequality lemma yields some terms with the inverse of convex and squared convex parameters, which often makes it difficult to find their bounds. Recently, reciprocal and second-order reciprocal convexity approaches have been proposed to handle the difficulties with a set of convex parameters and a set of squared convex parameters, respectively, but these approaches do not investigate the relation between the two sets. This paper offers much tighter bounds of those terms utilizing the relations among the two sets with the lower bound lemma. Based on the new approach and Lyapunov theory, less conservative stability criteria for time delay systems are developed. To show the effectiveness of the new approach, two numerical examples are given.

  • Auxiliary function-based integral/summation inequalities: Application to continuous/discrete time-delay systems

    PooGyeon Park, Won Il Lee, Seok Young Lee

    International Journal of Control, Automation and Systems

    AbstractIn the field of stability analysis for time-delay systems, finding precise bounds of integral/summation forms of quadratic functions plays a key role in reducing the conservatism. Consequently, there have been many attempts to develop inequalities yielding much tighter bounds. This paper develops novel inequalities using intermediate terms called auxiliary functions, which includes the existing inequalities as special cases. The stability conditions for continuous/discrete time-delay systems are derived in terms of linear matrix inequalities (LMIs) by using the proposed inequalities with simple numerical examples.

  • Special issue on time-delay systems and their applications

    Ju H Park, PooGyeon Park

    International Journal of Control, Automation and Systems

  • Stability analysis of discrete‐time systems with time‐varying delays: generalized zero equalities approach

    Seok Young Lee, Won Il Lee, PooGyeon Park

    International Journal of Robust and Nonlinear Control

    AbstractThis paper suggests a generalized zero equality lemma for summations, which leads to making a new Lyapunov–Krasovskii functional with more state terms in the summands and thus applying various zero equalities for deriving stability criteria of discrete-time systems with interval time-varying delays. Also, using a discrete-time counter part of Wirtinger-based integral inequality, Jensen inequality, and a lower bound lemma for reciprocal convexity, the forward difference of the Lyapunov–Krasovskii functional is bounded by the combinations of various state terms including not only summation terms but also their interval-normalized versions, which contributes to making the criteria less conservative. Numerical examples show the improved performance of the criteria in terms of maximum delay bounds.

  • A robust affine projection sign algorithm against the high power of measurement noises

    JinWoo Yoo, JaeWook Shin, Insun Song, P Park

    International Journal of Communication Systems

    AbstractThis paper proposes a novel robust affine projection sign algorithm (R-APSA) through a modified criterion that consists of the Euclidean norm of the sum of the difference between the present weight vector and the previous weight vectors. Because the filter update equation of the proposed R-APSA is obtained from the modified criterion, it has robustness against the high power of measurement noises. Moreover, due to the characteristic inherent in the original APSA, the proposed R-APSA performs well even though impulsive noises occur. Simulation results verify that the proposed R-APSA attains smaller steady-state errors than the existing released algorithms.

  • A variable step-size diffusion normalized least-mean-square algorithm with a combination method based on mean-square deviation

    Sang Mok Jung, Ji-Hye Seo, PooGyeon Park

    Circuits, Systems, and Signal Processing

    A novel diffusion normalized least-mean-square algorithm is proposed for distributed network. For the adaptation step, the upper bound of the mean-square deviation (MSD) is derived instead of the exact MSD value, and then, the variable step size is obtained by minimizing it to achieve fast convergence rate and small steady-state error. For the diffusion step, the individual estimate at each node is constructed via the weighted sum of the intermediate estimates at its neighbor nodes, where the weights are designed by using a proposed combination method based on the MSD at each node. The proposed MSD-based combination method provides effective weights by using the MSD at each node as a reliability indicator. Simulations in a system identification context show that the proposed algorithm outperforms other algorithms in the literatures.