Institute for Systems Research
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Item Convergence Results for Ant Routing Algorithms via Stochastic Approximation and Optimization(2007) Purkayastha, Punyaslok; Baras, John S.``Ant algorithms'' have been proposed to solve a variety of problems arising in optimization and distributed control. They form a subset of the larger class of ``Swarm Intelligence'' algorithms. The central idea is that a "swarm" of relatively simple agents can interact through simple mechanisms and collectively solve complex problems. Instances that exemplify the above idea abound in nature. The abilities of ant colonies to collectively accomplish complex tasks have served as sources of inspiration for the design of ``Ant algorithms''. Examples of ``Ant algorithms'' are the set of ``Ant Routing'' algorithms that have been proposed for communication networks. We analyze in this paper Ant Routing Algorithms for packet-switched wireline networks. The algorithm retains most of the salient and attractive features of Ant Routing Algorithms. The scheme is a multiple path probabilistic routing scheme, that is fully adaptive and distributed. Using methods from adaptive algorithms and stochastic approximation, we show that the evolution of the link delay estimates can be closely tracked by a deterministic ODE system. A study of the equilibrium points of the ODE gives us the equilibrium behavior of the routing algorithm, in particular, the equilibrium routing probabilities, and mean delays in the links under equilibrium. We also show that the fixed-point equations that the equilibrium routing probabilities satisfy are actually the necessary and sufficient conditions of an appropriate optimization problem. Simulations supporting the analytical results are provided.Item Comparison of Run-to-Run Control Methods in Semiconductor Manufacturing Processes(2000) Zhang, Chang; Deng, Hao; Baras, John S.; Baras, John S.; ISRRun-to Run (RtR) control plays an important role in semiconductor manufacturing.In this paper, RtR control methods are generalized. The set-valued RtR controllers with ellipsoidapproximation are compared with other RtR controllers bysimulation according to the following criteria: A good RtR controller should be able to compensate for variousdisturbances, such as process drifts, process shifts (step disturbance)and model errors; moreover, it should beable to deal with limitations, bounds, cost requirement, multipletargets and time delays that are often encountered in realprocesses.
Preliminary results show the good performance of the set-valued RtRcontroller. Furthermore, this paper shows that it is insufficient to uselinear models to approximate nonlinear processes and it is necessary to developnonlinear model based RtR controllers.
Item The Set-Valued Run-to-Run Controller with Ellipsoid Approximation(2000) Zhang, Chang; Baras, John S.; Baras, John S.; ISRIn order to successfully apply Run-to-Run (RtR) control or real time control ina semiconductor process, it is very important to estimate the processmodel. Traditional semiconductor process control methods neglect theimportance of robustness due to the estimation methods they use.A new approach, namely the set-valued RtR controller with ellipsoidapproximation, is proposed to estimate the process model from acompletely different point of view. Because the set-valued RtRcontroller identifies the process model in the feasible parameter setwhich is insensitive to noises, the controller is robust to theenvironment noises.Ellipsoid approximation can significantly reduce the computation load for the set-valued method.
In this paper, the Modified Optimal Volume Ellipsoid (MOVE) algorithm is used toestimate the process model in each run. Designof the corresponding controller and parameter selection of the controller are introduced.Simulation results showed that the controller is robust toenvironment noises and model errors.
Item Run-to-Run Control Methods Based on the DHOBE Algorithm(1999) Deng, Hao; Zhang, Chang; Baras, John S.; ISR; CSHCNMany run-to-run (RtR) control methods have been developed in recentyears. Two particular set-valued RtR control schemes based on the Dasgupta-Huang OptimalBounded Ellipsoid (DHOBE) algorithm are introduced. Compared to other RtR control schemes, the methods in this paper only need to know the bound of the noises, and are easyto implement.The DHOBE algorithm, for eachrecursion, returns an outer bounding ellipsoid of the estimated parameters. If the center of the ellipsoid each time istaken as the model coefficients, the explicit model update isimplemented which leads to a model-reference method. If we choose theworst-case point which maximizes the cost function in the set, then wecan apply the set-valued worst case approach. These two methods were compared with two other main RtRcontrol schemes: the Exponentially Weighted Moving Average (EWMA) methodand the Optimizing Adaptive Quality Controller (OAQC) method. Simulation results showed the superior performance of the RtRcontrollers based on the DHOBE algorithm. Furthermore this paper showedthat it is necessary to applynonlinear models to compensate for severe nonlinear processes.
Item Estimation of Hidden Markov Models for Partially Observed Risk Sensitive Control Problems(1997) Frankpitt, Bernard A.; Baras, John S.; ISRWe look at the problem of estimation for partially observed, risk-sensitive control problems with finite state, input and output sets, and receding horizon. We describe architectures for risk sensitive controllers, and estimation, and we state conditions under which both the estimated model converges to the true model, and the control policy will converge to the optimal risk sensitive policy.Item A Dynamic Routing Algorithm in Mixed Media Networks with Integrated Voice and Data Traffic(1993) Chen, Shih-Wei; Baras, John S.; ISR; CSHCNIn this paper, we consider mixed media networks with multi-media traffic to find the optimal splitting ratio between satellite network and terrestrial network for data and voice traffic dynamically. We constantly monitor the traffic and measure the arrival rate and occupancy of every link. Based on these data, we optimize data traffic delay in a suitable time-frame under the constraints of voice traffic blocking probabilities of voice transmission links being less than specified value, which is up to system's design or users' requirements. A dynamic routing algorithm is presented.Item Robust Output Feedback Control for Discrete - Time Nonlinear Systems(1993) James, Matthew R.; Baras, John S.; ISRIn this paper we present a new approach to the solution of the output feedback robust control problem. We employ the recently developed concept of information state for output feedback dynamic games, and obtain necessary and sufficient conditions for the solution to the robust control problem expressed in terms of the information state. The resulting controller is an information state feedback controller, and is intrinsically infinite dimensional. Stability results are obtained using the theory of dissipative systems, and indeed, our results are expressed in terms of dissipation inequalities.Item Consideration on Optimal Design of Distributed Sensors and Actuators Made of Smart Materials for Active Vibration Control(1993) Zhuang, Y.; Baras, John S.; ISRWe describe a design technique for optimal control in active structural vibration damping using smart materials. The vibration of a cantilever beam is stabilized by using distributed sensors and actuators. We model the beam by the Timoshenko beam model together with the distributed sensors and actuators. A control law using the weighted integration of vibration velocity is incorporated in the closed loop system. We propose a method to find the optimal layout design of the smart material so as to maximize the damping effect. An objective functional is defined based on the vibration energy of the system. The optimal shapes of the sensor and actuator are determined through minimizing the energy functional of the beam over the admissible shaped function space subject to certain geometric constraints. An algorithm has been developed to determine the optimal sensor and actuator layout. This method can be generalized to the plate damping problem and more complicated structures as well.