In this paper sensitivity minimization problem is considered for a class of unstable time delay systems. Our goal is to find a stable controller stabilizing the feedback system and giving rise to smallest Hinfinnorm for the sensitivity function. This problem has been solved by Ganesh and Pearson (1986) for finite dimensional plants using Nevanlinna-Pick interpolation. We extend their technique to include possibly unstable time delay systems. Moreover, we illustrate suboptimal solutions, and their robust implementation

It has been shown that the TCP connections through the congested routers can be modeled as a feedback dynamic system. In this paper, we design a variable structure (VS) based control scheme in active queue management (AQM) supporting explicit congestion notification (ECN). By analyzing the robustness and performance of the control scheme for nonlinear TCP/AQM model, we show that the proposed design has good performance and robustness with respect to the uncertainties of the round-trip time (RTT) and the number of active TCP sessions, which are central to the notion of AQM. Implementation issues are discussed and ns simulations are provided to validate the design and compare its performance to other peer schemes' in different scenarios. The results show that the proposed design significantly outperforms the peer AQM schemes in terms of packet loss ratio, throughput and buffer fluctuation.

Biological systems are highly nonlinear, have at least one pair of muscles actuating every degree of freedom at any joint, and possess neural transmission delays in their feedforward (efferent) and feedback (afferent) paths. This nonlinear time delay system, involved in movement and continuous interaction with the environment, is precise, stable, and very adaptive. The problem of trajectory tracking control of a three-link sagittal model of the shank, thigh and trunk is considered in this study. The controller is synthesized using the Q-parameterization method of controller design, for the class of stable nonlinear systems. The "free design" parameter is chosen to achieve certain performance and robustness objectives, the standard approach in H/sup /spl infin// control design. Performance of the system to a class of reference inputs and robustness issues pertaining to neglected nonlinearities, unmodeled dynamics and uncertainties in time delays, are addressed in the problem. Simulations are conducted to test the performance and feasibility of the controller for the task of squatting.