Hagbae Kim

A new intelligent digital redesign for T-S fuzzy systems: global approach

This paper proposes a novel and efficient global intelligent digital redesign technique for a Takagi-Sugeno (T-S) fuzzy system. The term of intelligent digital redesign involves converting an existing analog fuzzy-model-based controller into an equivalent digital counterpart in the sense of state-matching. The proposed method should be notably discriminated from the previous works in that it allows us to globally match the states of the overall closed-loop T-S fuzzy system with the predesigned analog fuzzy-model-based controller and those with the digitally redesigned fuzzy-model-based controller, and further to examine the stabilizability by the redesigned controller in the sense of Lyapunov. The key idea is that the global intelligent digital redesign problem is viewed as a convex minimization problem of the norm distance between nonlinearly interpolated linear operators to be matched. Sufficient conditions for the global state-matching and the stability of the digitally controlled system are formulated in terms of linear matrix inequalities (LMIs). A complex nonlinear system, Duffing-like chaotic oscillator is simulated and demonstrated to validate the feasibility and effectiveness of the proposed digital redesign technique, which implies the safe applicability to the digital control system.

Derivation and application of hard deadlines for real-time control systems

A method for calculating the hard deadlines in linear time-invariant control systems by considering system stability and the allowed state-space is presented. To derive necessary conditions for asymptotic system stability, the state difference equation is modified based on an assumed maximum delay and the probability distribution of delays whose magnitudes are less than, or equal to, the assumed maximum delay. The allowed state-space-which is derived from given input and state constraints-is used to calculate the hard deadline as a function of time and the system state. A one-shot delay model in which a single event causes a dynamic failure is considered. The knowledge of hard deadline is applied to the design of error recovery in a triple modular redundant controller computer. >

Performance Analysis of Location Estimation Algorithm in ZigBee Networks Using Received Signal Strength

This paper presents a maximum likelihood estimator (MLE) for the ZigBee networks. We propose a deployment of cluster-tree topology in the ZigBee networks and derive the MLE under the log-normal models for the Received Signal Strength (RSS) measurements. The ZiLA algorithm is also proposed to apply the MLE to ZigBee networks. To validate the RSS measurement model, we have conducted exhaustive experiments. Testbed experiments are also conducted to validate the effectiveness of ZiLA algorithm.

On the maximum feedback delay in a linear/nonlinear control system with input disturbances caused by controller-computer failures

Electromagnetic interferences or other environmental disturbances may cause transient failures to the controller computer of a real-time control system. Such a faulty controller either fails to update the control input for one or more sampling periods, or generates erroneous control inputs until the failure is handled properly or disappears. The goal of this paper is to derive the maximum duration of controllers faulty behavior, called the hard deadline, a real-time control system can tolerate without losing stability or leaving its allowed state space. For linear time-invariant control systems, one can derive hard deadlines by testing the stability of their state difference equations which account for the effects of stationary occurrences of disturbances to, as well as the random delays in, the control input. Similarly, one can derive deadlines for nonlinear time-invariant control systems by linearizing their nonlinear state equations and using the Lyapunovs first method. In addition to this stationary model, a one-shot event model is considered for linear/nonlinear time-invariant control systems by using their state trajectories and allowed state spaces. The hard deadline information that represents the knowledge of the controlled processs inertia and timing constraints is applied to the design and evaluation of controller computers. >

Color segmentation robust to brightness variations by using B-spline curve modeling

Color segmentation takes a great attention because color is an effective and robust visual cue for characterizing an object from the others. However, color segmentation suffers from color variations incurred by irregular illumination changes. We propose a reliable color modeling approach in hue-saturation-intensity (HSI) color space while considering intensity information by adopting the B-spline curve fitting to make a mathematical model for statistical characteristics of a color with respect to intensity. It is based on the fact that color distribution of a single-colored object is not invariant with respect to brightness variations even in the HS (hue-saturation) plane. The statistical characteristics contain the mean and standard deviation of hue and saturation with respect to intensity. They are mathematically expressed as four bar graphs. In order to fit the bar graphs to continuous curves, we use B-spline curve fitting procedure. From several experimental results, we verify that the proposed algorithm is successfully applied to color segmentation under various illumination conditions.

Effects of electromagnetic interference on controller-computer upsets and system stability

Electromagnetic interference (EMI) causes controller upsets manifested as errors in control-law computation on a controller computer, or as disturbances in data transmission between sensors/actuators and the controller computer, which may be critical to system stability. We compute the probability of these EMI-induced upsets in terms of the parameters governing EMI behaviors and the conditional probabilities of upsets in the presence of EMI, which is useful for the design and verification of the integrity of reliable controllers. The results are used to modify a system dynamic equation to examine asymptotic stability with probability one for the random sequences of the system states evolving according to the resultant dynamic equation, which are validated via a simple EMI experiment in a reverberation chamber.

Evaluation of fault tolerance latency from real-time application's perspectives

Information on Fault Tolerance Latency (FTL), which is defined as the total time required by all sequential steps taken to recover from an error, is important to the design and evaluation of fault-tolerant computers used in safety-critical real-time control systems with deadline information. In this paper, we evaluate FTL in terms of several random and deterministic variables accounting for fault behaviors and/or the capability and performance of error-handling mechanisms, while considering various fault tolerance mechanisms based on the trade-off between temporal and spatial redundancy, and use the evaluated FTL to check if an error-handling policy can meet the Control System Deadline (CSD) for a given real-time application.

ZigBee Based Location Estimation in Home Networking Environments

This paper presents a Maximum Likelihood Location Estimation (MLLE) algorithm for the home network environments. We propose a deployment of cluster-tree topology in the ZigBee networks and derive the MLE under the log-normal models for the Received Signal Strength (RSS) measurements. Experiments are also conducted to validate the effectiveness of the proposed algorithm.

Development of a Residential Gateway and a Service Server for Home Automation

We have developed a residential gateway that centralizes device interfacing between the external Internet and internal devices as well as appliance networks. We have also proposed the concept of a service server to be implemented for a large scale of apartment complex or a wide area house. The primary components of the residential gateway to be implemented in this paper include a processor(Motorola MPC8240), persistent storage(flash RAM, extend storage device), networking modules (such as TCP/IP for Ethernet, ADSL), home networking(HomePNA, IEEE1394, PLC), device interfaces(serial or PCI), home automation, and telecommunication system (PSTN/SLT, VoIP, Video Communication), which are typically powered by a certain RTOS. Finally, we have test results validating the effectiveness of both the residential gateway and the service server.

Reliability modeling of hard real-time systems

A hard real-time control system, such as a fly-by-wire system, fails catastrophically (e.g., lose stability) if its control input is not updated by its digital controller computer within a certain time limit called the hard deadline. To assess and validate system reliability by using a semi-Markov model that explicitly contains the deadline information, we propose a path-space approach deriving the upper and lower bounds of the probability of system failure. These bounds are derived by using only simple parameters, and they are especially suitable for highly-reliable systems which must recover quickly. Analytical bounds are derived for both exponential and Weibull failure distributions, which have proven effective through numerical examples, while considering three repair strategies: repair-as-good-as-new, repair-as-good-as-old, and repair-better-than-old.