Wook Hyun Kwon

Delay-dependent robust stabilization of uncertain state-delayed systems

This paper concerns a problem of robust stabilization of uncertain state-delayed systems. A new delay-dependent stabilization condition using a memoryless controller is formulated in terms of matrix inequalities. An algorithm involving convex optimization is proposed to design a controller guaranteeing a suboptimal maximal delay such that the system can be stabilized for all admissible uncertainties.

Feedback stabilization of linear systems with delayed control

Feedback controls based on the receding horizon method have proven to be a useful and easy tool in stabilizing linear ordinary differential systems. In this paper the receding horizon method is applied to linear systems with delay in the control. An open-loop optimal control which minimizes control energy subject to certain side constraints is first derived and then transformed to a closed-loop control via the receding horizon concept. The resulting feedback system is shown to be asymptotically stable under a complete controllability condition. It is also shown how the receding horizon control suggests a more general class of stabilizing feedback control laws. The control laws of this paper are perhaps the easiest way to stabilize a linear system with delay in the control.

Maximum allowable delay bounds of networked control systems

This paper proposes a new method to obtain a maximum allowable delay bound for a scheduling of networked control systems. The proposed method is formulated in terms of linear matrix inequalities and can give a much less conservative delay bound than the existing methods. A network scheduling method is presented based on the delay obtained through the proposed method, the bandwidth of a network is allocated to each node and the sampling period of each sensor and controller is determined. The presented method can handle three types of data (periodic data, sporadic data, and message) and guarantees real-time transmission of periodic and sporadic data, and minimum network utilization for non-real time message.

Minimum-energy asynchronous dissemination to mobile sinks in wireless sensor networks

Data dissemination from sources to sinks is one of the main functions in sensor networks. In this paper, we propose SEAD, a Scalable Energy-efficient Asynchronous Dissemination protocol, to minimize energy consumption in both building the dissemination tree and disseminating data to mobile sinks. SEAD considers the distance and the packet traffic rate among nodes to create near-optimal dissemination trees. The sinks can move without reporting their location to the tree while receiving data updates successfully. Our evaluation results illustrate that SEAD consumes less energy on building and maintaining a dissemination tree to multiple mobile sinks compared to other approaches such as directed diffusion, TTDD, and mobile ad hoc multicast.

Memoryless H/sup /spl infin// controllers for state delayed systems

In this note, a memoryless H/sup /spl infin// controller for the state delayed system is presented. The controller is a delay independent stabilizer for the state delayed system, which also reduces the H/sup /spl infin// norm of the closed loop transfer function, from the disturbance to the controlled output, to a prescribed level. The controller can be obtained by solving a modified Riccati equation. >

A scheduling method for network-based control systems

This paper presents a scheduling method for network-based control systems with three types of data (periodic data, sporadic data, and messages). As a basic parameter for the scheduling method for network-based control systems, a maximum allowable delay bound is used,which guarantees stability of network-based control systems and is derived from characteristics of the given plant using the presented theorems. The presented scheduling method for network-based control systems can adjust the sampling period as small as possible, allocate the bandwidth of the network for three types of data, and exchange the transmission orders of data for sensors and actuators. In addition, the presented scheduling method guarantees real-time transmission of sporadic and periodic data, and minimum utilization for nonreal-time messages. The proposed method is shown to be useful by examples.

On feedback stabilization of time-varying discrete linear systems

Results are given for stabilizing time-varying discrete linear systems by means of a feedback control stemming from a receding-horizon concept and a minimum quadratic cost with a fixed terminal constraint. The results parallel those recently obtained for continuous-time systems [8] and extend a well-known method of Kleinman for stabilizing discrete fixed linear systems [7].

Delay-Dependent Robust Stabilization of Uncertain Time-Delay Systems

Abstract This paper concerns robust stabilization of uncertain time-delay systems. An improved upper bound for the inner product of two vectors is introduced, and used to derive new delay-dependent robust stability and stabilization conditions. An algorithm is also proposed to construct a robust stabilizing controller with a supoptimal maximal delay such that the system can be stabilized with the controller for all admissible uncertainties. It is illustrated by numerical examples that the proposed delay-dependent controller can be less conservative than existing results and it is even possible to capture the delay-independent stabilizability of the system.

Packet Error Rate Analysis of ZigBee Under WLAN and Bluetooth Interferences

In this paper, the performance of IEEE 802.15.4 ZigBee under the interference of IEEE 802.11b wireless local area network (WLAN) and/or Bluetooth is evaluated using an analytic model for the coexistence among ZigBee, WLAN, and Bluetooth. The packet error rate (PER) is evaluated, where the PER is obtained from the bit error rate (BER) and the collision time. The BER is obtained from the signal-to-interference-plus-noise ratio (SINR). Finally, the analytic results are validated by simulations.

A receding horizon Kalman FIR filter for discrete time-invariant systems

A receding horizon Kalman FIR filter is presented that combines the Kalman filter and the receding horizon strategy when the horizon initial state is assumed to be unknown. The suggested filter is a FIR filter form which has many good inherent properties. It can always be defined irrespective of singularity problems caused by unknown information about the horizon initial state. The suggested filter can be represented in either an iterative form or a standard FIR form. It is also shown that the suggested filter possesses the unbiasedness property and the remarkable deadbeat property irrespective of any horizon initial condition. The validity of the suggested filter is illustrated by numerical examples.