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516
Walking the tightrope: Responsive yet stable traffic engineering
- In Proc. ACM SIGCOMM
, 2005
"... Current intra-domain Traffic Engineering (TE) relies on offline methods, which use long term average traffic demands. It cannot react to realtime traffic changes caused by BGP reroutes, diurnal traffic variations, attacks, or flash crowds. Further, current TE deals with network failures by pre-compu ..."
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Cited by 159 (3 self)
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Current intra-domain Traffic Engineering (TE) relies on offline methods, which use long term average traffic demands. It cannot react to realtime traffic changes caused by BGP reroutes, diurnal traffic variations, attacks, or flash crowds. Further, current TE deals with network failures by pre-computing alternative routings for a limited set of failures. It may fail to prevent congestion when unanticipated or combination failures occur, even though the network has enough capacity to handle the failure. This paper presents TeXCP, an online distributed TE protocol that balances load in realtime, responding to actual traffic demands and failures. TeXCP uses multiple paths to deliver demands from an ingress to an egress router, adaptively moving traffic from overutilized to under-utilized paths. These adaptations are carefully designed such that, though done independently by each edge router based on local information, they balance load in the whole network without oscillations. We model TeXCP, prove the stability of the model, and show that it is easy to implement. Our extensive simulations show that, for the same traffic demands, a network using TeXCP supports the same utilization and failure resilience as a network that uses traditional offline TE, but with half or third the capacity.
Spaceex: Scalable verification of hybrid systems
- In Proceedings of the International Conference on Computer Aided Verification
, 2011
"... Abstract. We present a scalable reachability algorithm for hybrid systems with piecewise affine, non-deterministic dynamics. It combines polyhedra and support function representations of continuous sets to compute an over-approximation of the reachable states. The algorithm improves over previous wo ..."
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Cited by 86 (5 self)
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Abstract. We present a scalable reachability algorithm for hybrid systems with piecewise affine, non-deterministic dynamics. It combines polyhedra and support function representations of continuous sets to compute an over-approximation of the reachable states. The algorithm improves over previous work by using variable time steps to guarantee a given local error bound. In addition, we propose an improved approximation model, which drastically improves the accuracy of the algorithm. The algorithm is implemented as part of SpaceEx, a new verification platform for hybrid systems, available at spaceex.imag.fr. Experimental results of full fixed-point computations with hybrid systems with more than 100 variables illustrate the scalability of the approach. 1
A Method for Handling Uncertainty in Evolutionary Optimization with an Application to Feedback Control of Combustion
"... Abstract — We present a novel method for handling uncertainty in evolutionary optimization. The method entails quantification and treatment of uncertainty and relies on the rank based selection operator of evolutionary algorithms. The proposed uncertainty handling is implemented in the context of th ..."
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Cited by 50 (14 self)
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Abstract — We present a novel method for handling uncertainty in evolutionary optimization. The method entails quantification and treatment of uncertainty and relies on the rank based selection operator of evolutionary algorithms. The proposed uncertainty handling is implemented in the context of the Covariance Matrix Adaptation Evolution Strategy (CMA-ES) and verified on test functions. The present method is independent of the uncertainty distribution, prevents premature convergence of the evolution strategy and is well suited for online optimization as it requires only a small number of additional function evaluations. The algorithm is applied in an experimental set-up to the online optimization of feedback controllers of thermoacoustic instabilities of gas turbine combustors. In order to mitigate these instabilities, gain-delay or model-based H ∞ controllers sense the pressure and command secondary fuel injectors. The parameters of these controllers are usually specified via a trial and error procedure. We demonstrate that their online optimization with the proposed methodology enhances, in an automated fashion, the online performance of the controllers, even under highly unsteady operating conditions, and it also compensates for uncertainties in the model-building and design process. I.
The quadruple-tank process: A multivariable laboratory process with an adjustable zero
- IEEE Trans. on Control Systems Technology
"... Abstract—A novel multivariable laboratory process that consists of four interconnected water tanks is presented. The linearized dynamics of the system have a multivariable zero that is possible to move along the real axis by changing a valve. The zero can be placed in both the left and the right hal ..."
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Cited by 48 (0 self)
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Abstract—A novel multivariable laboratory process that consists of four interconnected water tanks is presented. The linearized dynamics of the system have a multivariable zero that is possible to move along the real axis by changing a valve. The zero can be placed in both the left and the right half-plane. In this way the quadruple-tank process is ideal for illustrating many concepts in multivariable control, particularly performance limitations due to multivariable right half-plane zeros. The location and the direction of the zero have an appealing physical interpretation. Accurate models are derived from both physical and experimental data and decentralized control is demonstrated on the process. Index Terms—Education, laboratory process, multivariable control, multivariable zeros. I.
From experiment design to closed-loop control
, 2005
"... The links between identification and control are examined. The main trends in this research area are summarized, with particular focus on the design of low complexity controllers from a statistical perspective. It is argued that a guiding principle should be to model as well as possible before any m ..."
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Cited by 43 (1 self)
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The links between identification and control are examined. The main trends in this research area are summarized, with particular focus on the design of low complexity controllers from a statistical perspective. It is argued that a guiding principle should be to model as well as possible before any model or controller simplifications are made as this ensures the best statistical accuracy. This does not necessarily mean that a full-order model always is necessary as well designed experiments allow for restricted complexity models to be near-optimal. Experiment design can therefore be seen as the key to successful applications. For this reason, particular attention is given to the interaction between experimental constraints and performance specifications.
Attack detection and identification in cyber-physical systems
- IEEE Trans. Automat. Contr
"... Cyber-physical systems are ubiquitous in power systems, transportation networks, industrial process control and critical infrastructures. These systems need to operate reliably in the face of unforeseen failures and external malicious attacks. In this paper (i) we propose a mathematical framework fo ..."
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Cited by 30 (4 self)
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Cyber-physical systems are ubiquitous in power systems, transportation networks, industrial process control and critical infrastructures. These systems need to operate reliably in the face of unforeseen failures and external malicious attacks. In this paper (i) we propose a mathematical framework for cyberphysical systems, attacks, and monitors; (ii) we characterize fundamental monitoring limitations from system-theoretic and graph-theoretic perspectives; and (iii) we design centralized and distributed attack detection and identification monitors. Finally, we validate our findings through compelling examples. I.
Bandit problems
- Proceedings of the Seventh International Berry
, 1985
"... the formulation and solution of robust performance ..."
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Cited by 23 (1 self)
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the formulation and solution of robust performance
Issues, progress and new results in robust adaptive control
- ADAPTIVE CONTROL AND SIGNAL PROCESSING
, 2006
"... We overview recent progress in the field of robust adaptive control with special emphasis on methodologies that use multiple-model architectures. We argue that the selection of the number of models, estimators and compensators in such architectures must be based on a precise definition of the robust ..."
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Cited by 21 (6 self)
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We overview recent progress in the field of robust adaptive control with special emphasis on methodologies that use multiple-model architectures. We argue that the selection of the number of models, estimators and compensators in such architectures must be based on a precise definition of the robust performance requirements. We illustrate some of the concepts and outstanding issues by presenting a new methodology that blends robust nonadaptive mixed µ-synthesis designs and stochastic hypothesis-testing concepts leading to the so-called Robust Multiple Model Adaptive Control (RMMAC) architecture. A numerical example is used to illustrate the RMMAC design methodology, as well as its strengths and potential shortcomings. The later motivated us to develop a variant architecture, denoted as RMMAC/XI, that can be effectively used in highly uncertain exogenous plant disturbance environments.
Combined feedforward/feedback control of atomic force microscopes
- IN PROC. AMER. CTRL. CONF
, 2007
"... The Atomic Force Microscope (AFM) is a powerful imaging and nanofabrication tool that allows the user to observe and manipulate samples at the atomic level. However, one limitation of current AFMs is the long time required to obtain a quality image of a sample. Several researchers have investigate ..."
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Cited by 21 (8 self)
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The Atomic Force Microscope (AFM) is a powerful imaging and nanofabrication tool that allows the user to observe and manipulate samples at the atomic level. However, one limitation of current AFMs is the long time required to obtain a quality image of a sample. Several researchers have investigated this problem in recent years, and we give an overview of the approaches explored, including H∞, ℓ1, and model-inverse based methods. We compare and discuss advantages and disadvantages of the various approaches, and we end with a summary of open questions to be addressed in improving the control of AFMs.
