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  • 101. Ren, Xiaoqiang
    et al.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shi, Ling
    Quickest Change Detection With Observation Scheduling2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 6, p. 2635-2647Article in journal (Refereed)
    Abstract [en]

    The quickest change detection problem is to detect an abrupt change event as quickly as possible subject to constraints on false detection. Unlike the classical problem, where the decision maker can access only one sequence of observations, in this paper, the decision maker chooses one of two different sequences of observations at each time instant. The information quality and sampling cost of the two sequences of observations are different. We present an asymptotically optimal joint design of observation scheduling policy and stopping time such that the detection delay is minimized subject to constraints on both average run length to false alarm (ARLFA) and average cost per sample. The observation scheduling policy has a threshold structure and the detection scheme is a variant of the cumulative sum test where the detection statistic stochastically crosses the threshold that is used to switch observation modes. We further study the decentralized case in a multi-channel setting. We show that if each sensor uses the proposed observation scheduling policy locally and the fusion center uses the Nsum algorithm, by which the center declares the change when the sum of the sensors' local detection statistics crosses a certain threshold, the detection delay is asymptotically minimized for any possible combination of the affected sensors subject to constraints on both global ARLFA and average cost per sample at each sensor node. Numerical examples are given to illustrate the main results.

  • 102. Ren, Xiaoqiang
    et al.
    Wu, Junfeng
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Shi, Guodong
    Shi, Ling
    Infinite Horizon Optimal Transmission Power Control for Remote State Estimation Over Fading Channels2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 1, p. 85-100Article in journal (Refereed)
    Abstract [en]

    This paper studies the joint design over an infinite horizon of the transmission power controller and remote estimator for state estimation over fading channels. A sensor observes a dynamic process and sends its observations to a remote estimator over a wireless fading channel characterized by a time-homogeneous Markov chain. The successful transmission probability depends on both the channel gains and the transmission power used by the sensor. The transmission power control rule and the remote estimator should be jointly designed, aiming to minimize an infinite-horizon cost consisting of the power usage and the remote estimation error. We formulate the joint optimization problem as an average cost belief-state Markov decision process and prove that there exists an optimal deterministic and stationary policy. We then show that when the monitored dynamic process is scalar or the system matrix is orthogonal, the optimal remote estimates depend only on the most recently received sensor observation, and the optimal transmission power is symmetric and monotonically increasing with respect to the norm of the innovation error.

  • 103.
    Rojas, Cristian R.
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Agüero, Juan C.
    The University of Newcastle, Australia.
    Welsh, James S.
    The University of Newcastle, Australia.
    Goodwin, Graham C.
    The University of Newcastle, Australia.
    Feuer, Arie
    Technion, Israel.
    Robustness in Experiment Design2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 4, p. 860-874Article in journal (Refereed)
    Abstract [en]

    This paper focuses on the problem of robust experiment design, i.e., how to design an input signal which gives relatively good estimation performance over a large number of systems and model structures. Specifically, we formulate the robust experiment design problem utilizing fundamental limitations on the variance of estimated parametric models as constraints. Using this formulation we design an input signal for situations where only diffuse a priori information is known about the system. Furthermore, we present a robust version of the unprejudiced optimal input design problem. To achieve this, we first develop a closed form solution for the input spectrum which minimizes the maximum weighted integral of the variance of the frequency response estimate over all model structures.

  • 104.
    Rojas, Cristian R.
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Barenthin, Marta
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Welsh, James S.
    The University of Newcastle, Australia.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The Cost of Complexity in System Identification: Frequency Function Estimation of Finite Impulse Response Systems2010In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 55, no 10, p. 2298-2309Article in journal (Refereed)
    Abstract [en]

    In this paper, we consider full order modeling, i.e., when the true system belongs to the model set. We investigate the minimum amount of input energy required to estimate a given linear system with a full order model within a prescribed degree of accuracy gamma, as a function of the model complexity. This quantity we define to be the "cost of complexity." The degree of accuracy is measured by the inverse of the maximum variance of the discrete-time frequency function estimator over a given frequency range [-omega(B), omega(B)]. It is commonly believed that the cost increases as the model complexity increases. However, the amount of information that is to be extracted from the system also influences the cost. The objective of this paper is to quantify these dependencies for systems described by finite-impulse response models. It is shown that, asymptotically in the model order and sample size, the cost is well approximated by gamma sigma(2)(o)n omega(B)/pi where sigma(2)(o)is the noise variance. This expression can be used as a simple rule of thumb for assessing trade-offs that have to be made in a system identification project where full order models are used. For example, for given experiment duration, excitation level and desired accuracy, one can assess how the achievable frequency range depends on the required model order. This type of consideration is useful when formally planning experiments. In addition, we establish several properties of the cost of complexity. We find, for example, that if omega(B) is very close (but not necessarily equal) to pi, the optimal input satisfies the model quality constraint for all frequencies.

  • 105.
    Rojas, Cristian R.
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Toth, Roland
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sparse Estimation of Polynomial and Rational Dynamical Models2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 11, p. 2962-2977Article in journal (Refereed)
    Abstract [en]

    In many practical situations, it is highly desirable to estimate an accurate mathematical model of a real system using as few parameters as possible. At the same time, the need for an accurate description of the system behavior without knowing its complete dynamical structure often leads to model parameterizations describing a rich set of possible hypotheses; an unavoidable choice, which suggests sparsity of the desired parameter estimate. An elegant way to impose this expectation of sparsity is to estimate the parameters by penalizing the criterion with the l(0) "norm" of the parameters. Due to the non-convex nature of the l(0)-norm, this penalization is often implemented as solving an optimization program based on a convex relaxation (e. g., l(1)/LASSO, nuclear norm, ...). Two difficulties arise when trying to apply these methods: (1) the need to use cross-validation or some related technique for choosing the values of regularization parameters associated with the l(1) penalty; and (2) the requirement that the (unpenalized) cost function must be convex. To address the first issue, we propose a new technique for sparse linear regression called SPARSEVA, with close ties with the LASSO (least absolute shrinkage and selection operator), which provides an automatic tuning of the amount of regularization. The second difficulty, which imposes a severe constraint on the types of model structures or estimation methods on which the l(1) relaxation can be applied, is addressed by combining SPARSEVA and the Steiglitz-McBride method. To demonstrate the advantages of the proposed approach, a solid theoretical analysis and an extensive simulation study are provided.

  • 106.
    Rojas, Cristian R.
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Welsh, James S.
    The University of Newcastle, Australia.
    Agüero, Juan C.
    The University of Newcastle, Australia.
    Fundamental Limitations on the Variance of Estimated Parametric Models2009In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 54, no 5, p. 1077-1081Article in journal (Refereed)
    Abstract [en]

    In this technical note fundamental integral limitations are derived on the variance of estimated parametric models, for both open and closed loop identification. As an application of these results we show that, for multisine inputs, a well known asymptotic (in model order) variance expression provides upper bounds on the actual variance of the estimated models for finite model orders. The fundamental limitations established here give rise to a 'water-bed' effect, which is illustrated in an example.

  • 107.
    Rotkowitz, Michael
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Lall, Sanjay
    Affine controller parameterization for decentralized control over Banach spaces2006In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 51, no 9, p. 1497-1500Article in journal (Refereed)
    Abstract [en]

    We cast the problem of optimal decentralized control as one of minimizing a closed-loop norm subject to a subspace constraint on the controller. In this note, we consider continuous linear operators on Banach spaces, and show that a simple property called quadratic invariance is necessary and sufficient for the constraint set to be preserved under feedback, and thus allows optimal synthesis to be recast as a convex optimization problem. These results hold for any norm and any Banach space.

  • 108.
    Rotkowitz, Mikael
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Lall, S.
    A characterization of convex problems in decentralized control2005In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 50, no 12, p. 1984-1996Article in journal (Refereed)
    Abstract [en]

    We consider the problem of constructing optimal decentralized controllers. We formulate this problem as one of minimizing the closed-loop norm of a feedback system subject to constraints on the controller structure. We define the notion of quadratic invariance of a constraint set with respect to a system, and show that if the constraint set has this property, then the constrained minimum-norm problem may be solved via convex programming. We also show that quadratic invariance is necessary and sufficient for the constraint set to be preserved under feedback. These results are developed in a very general framework, and are shown to hold in both continuous and discrete time, for both stable and unstable systems, and for any norm. This notion unifies many previous results identifying specific tractable decentralized control problems, and delineates the largest known class of convex problems in decentralized control. As an example, we show that optimal stabilizing controllers may be efficiently computed in the case where distributed controllers can communicate faster than their dynamics propagate. We also show that symmetric synthesis is included in this classification, and provide a test for sparsity constraints to be quadratically invariant, and thus amenable to convex synthesis.

  • 109.
    Rotkowitz, Mikael
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Lall, S
    A characterization of convex problems in decentralized control2006In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 51, no 2, p. 274-286Article in journal (Refereed)
    Abstract [en]

    We consider the problem of constructing optimal decentralized controllers. We formulate this problem as one of minimizing the closed-loop norm of a feedback system subject to constraints on the controller structure. We define the notion of quadratic invariance of a constraint set with respect to a system, and show that if the constraint set has this property, then the constrained minimum-norm problem may be solved via convex programming. We also show that quadratic invariance is necessary and sufficient for the constraint set to be preserved under feedback. These results are developed in a very general framework, and are shown to hold in both continuous and discrete time, for both stable and unstable systems, and for any norm. This notion unifies many previous results identifying specific tractable decentralized control problems, and delineates the largest known class of convex problems in decentralized control. As an example, we show that optimal stabilizing controllers may be efficiently computed in the case where distributed controllers can communicate faster than their dynamics propagate. We also show that symmetric synthesis is included in this classification, and provide a test for sparsity constraints to be quadratically invariant, and thus amenable to convex synthesis.

  • 110.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    An Extension to Balanced Truncation With Application to Structured Model Reduction2010In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 55, no 4, p. 1038-1043Article in journal (Refereed)
    Abstract [en]

    Balanced truncation is a standard method for model reduction, possessing many desirable properties such as preservation of model stability and a priori error bounds. Balanced truncation is conducted using controllability and observability Gramians. Generalized Gramians can be found by solving a set of linear matrix inequalities. In this paper, we show that these linear matrix inequalities can be extended so that the number of decision variables are at least doubled, leading to the concept of extended Gramians. Herein it is shown that the desirable properties of balanced truncation also hold with extended Gramians. The extended Gramians are especially useful for improving error bounds and for models possessing additional structural constraints, as is demonstrated by means of examples herein.

  • 111. Sandberg, Henrik
    et al.
    Bernhardsson, B.
    A bode sensitivity integral for linear time-periodic systems2005In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 50, no 12, p. 2034-2039Article in journal (Refereed)
    Abstract [en]

    Bode's sensitivity integral is a well-known formula that quantifies some of the limitations in feedback control for linear time-invariant systems. In this note, we show that there is a similar formula for linear time-periodic systems. The harmonic transfer function is used to prove the result. We use the notion of roll-off 2, which means that the first time-varying Markov parameter is equal to zero. It then follows that the harmonic transfer function is an analytic operator and a trace class operator. These facts are used to prove the result.

  • 112.
    Sandberg, Henrik
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Delvenne, Jean-Charles
    Doyle, John C.
    On Lossless Approximations, the Fluctuation-Dissipation Theorem, and Limitations of Measurements2011In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 56, no 2, p. 293-308Article in journal (Refereed)
    Abstract [en]

    In this paper, we take a control-theoretic approach to answering some standard questions in statistical mechanics, and use the results to derive limitations of classical measurements. A central problem is the relation between systems which appear macroscopically dissipative but are microscopically lossless. We show that a linear system is dissipative if, and only if, it can be approximated by a linear lossless system over arbitrarily long time intervals. Hence lossless systems are in this sense dense in dissipative systems. A linear active system can be approximated by a nonlinear lossless system that is charged with initial energy. As a by-product, we obtain mechanisms explaining the Onsager relations from time-reversible lossless approximations, and the fluctuation-dissipation theorem from uncertainty in the initial state of the lossless system. The results are applied to measurement devices and are used to quantify limits on the so-called observer effect, also called back action, which is the impact the measurement device has on the observed system. In particular, it is shown that deterministic back action can be compensated by using active elements, whereas stochastic back action is unavoidable and depends on the temperature of the measurement device.

  • 113. Sandberg, Henrik
    et al.
    Möllerstedt, E.
    Bernhardsson, B.
    Frequency-domain analysis of linear time-periodic systems2005In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 50, no 12, p. 1971-1983Article in journal (Refereed)
    Abstract [en]

    In this paper, we study convergence of truncated representations of the frequency-response operator of a linear time-periodic system. The frequency-response operator is frequently called the harmonic transfer function. We introduce the concepts of input, output, and skew roll-off. These concepts are related to the decay rates of elements in the harmonic transfer function. A system with high input and output roll-off may be well approximated by a low-dimensional matrix function. A system with high skew roll-off may be represented by an operator with only few diagonals. Furthermore, the roll-off rates are shown to be determined by certain properties of Taylor and Fourier expansions of the periodic systems. Finally, we clarify the connections between the different methods for computing the harmonic transfer function that are suggested in the literature.

  • 114. Sandberg, Henrik
    et al.
    Rantzer, A.
    Balanced truncation of linear time-varying systems2004In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 49, no 2, p. 217-229Article in journal (Refereed)
    Abstract [en]

    In this paper, balanced truncation of linear time-varying systems is studied in discrete and continuous time. Based on relatively basic calculations with time-varying Lyapunov equations/inequalities we are able to derive both upper and lower error bounds for the truncated models. These results generalize well-known time-invariant formulas. The case of time-varying state dimension is considered. Input-output stability of all truncated balanced realizations is also proven. The method is finally successfully applied to a high-order model.

  • 115.
    Selivanov, Anton
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Tel Aviv Univ, Sch Elect Engn, IL-6997801 Tel Aviv, Israel.
    Fridman, Emilia
    Tel Aviv Univ, Sch Elect Engn, IL-6997801 Tel Aviv, Israel..
    Boundary Observers for a Reaction-Diffusion System Under Time-Delayed and Sampled-Data Measurements2019In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, no 8, p. 3385-3390Article in journal (Refereed)
    Abstract [en]

    We construct finite-dimensional observers for a one-dimensional reaction-diffusion system with boundary measurements subject to time-delays and data sampling. The system has a finite number of unstable modes approximated by a Luenberger-type observer. The remaining modes vanish exponentially. For a given reaction coefficient, we show how many modes one should use to achieve a desired rate of convergence. The finite-dimensional part is analyzed using appropriate Lyapunov-Krasovskii functionals that lead to linear matrix inequalitie (LMI)-based convergence conditions feasible for small enough time-delay and sampling period. The LMIs can be used to find appropriate injection gains.

  • 116.
    Shames, Iman
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bishop, Adrian N.
    Anderson, Brian D. O.
    Analysis of Noisy Bearing-Only Network Localization2013In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 58, no 1, p. 247-252Article in journal (Refereed)
    Abstract [en]

    Graph theory has been used to characterize the solvability of the sensor network localization problem with ideal (i.e., precisely known) bearing-only measurements between certain pairs of sensors and a limited amount of information about the position of certain nodes, i.e., anchors. In practice, however, bearing measurements will never be exact, and the equations whose solutions deliver sensor positions in the noiseless case may no longer have a solution. This technical brief argues that if the same conditions for localizability that exist in the noiseless case are satisfied and the bearing measurement errors are small enough (as will be formalized later in the technical brief), then the network will be approximately localizable, i.e., sensor position estimates can be found which are near the correct values. In particular, a bound on the position errors is found in terms of a bound on the bearing errors. Later, this bound is used to propose a method to select anchors to minimize the effect of noisy bearing measurements on the localization solution.

  • 117.
    Shames, Iman
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dasgupta, Soura
    Fidan, Baris
    Anderson, Brian D. O.
    Circumnavigation Using Distance Measurements Under Slow Drift2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 4, p. 889-903Article in journal (Refereed)
    Abstract [en]

    Consider an agent A at an unknown location, undergoing sufficiently slow drift, and a mobile agent B that must move to the vicinity of and then circumnavigate A at a prescribed distance from A. In doing so, B can only measure its distance from A, and knows its own position in some reference frame. This paper considers this problem, which has applications to surveillance and orbit maintenance. In many of these applications it is difficult for B to directly sense the location of A, e.g. when all that B can sense is the intensity of a signal emitted by A. This intensity does, however provide a measure of the distance. We propose a nonlinear periodic continuous time control law that achieves the objective using this distance measurement. Fundamentally, a) B must exploit its motion to estimate the location of A, and b) use its best instantaneous estimate of where A resides, to move itself to achieve the circumnavigation objective. For a) we use an open loop algorithm formulated by us in an earlier paper. The key challenge tackled in this paper is to design a control law that closes the loop by marrrying the two goals. As long as the initial estimate of the source location is not coincident with the intial position of B, the algorithm is guaranteed to be exponentially convergent when A is stationary. Under the same condition, we establish that when A drifts with a sufficiently small, unknown velocity, B globally achieves its circumnavigation objective, to within a margin proportional to the drift velocity.

  • 118. Shi, Dawei
    et al.
    Guo, Ziyang
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shi, Ling
    Causality Countermeasures for Anomaly Detection in Cyber-Physical Systems2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 2, p. 386-401Article in journal (Refereed)
    Abstract [en]

    The problem of attack detection in cyber-physical systems is considered in this paper. Transferentropy-based causality countermeasures are introduced for both sensor measurements and innovation sequences, which can be evaluated in a data-driven fashion without relying on a model of the underlying dynamic system. The relationships between the countermeasures and the system parameters as well as the noise statistics are investigated, based on which conditions that guarantee the time convergence of the countermeasures are obtained. The effectiveness of the transfer entropy countermeasures in attack detection is evaluated via theoretical analysis, numerical demonstrations, as well as comparative simulations with classical chi(2) detectors. Four types of attacks are considered: denial-of-service, replay, innovation-based deception, and data injection attacks. Abnormal behavior of the transfer entropy can be observed after the occurrence of each of these attacks.

  • 119.
    Shi, Guodong
    et al.
    Australian Natl Univ, Res Sch Engn, Canberra, ACT 0200, Australia..
    Dong, Daoyi
    Univ New S Wales, Sch Informat Technol & Engn, Canberra, ACT 2600, Australia..
    Petersen, Ian R.
    Univ New S Wales, Sch Informat Technol & Engn, Canberra, ACT 2600, Australia..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. Royal Inst Technol, Sch Elect Engn, ACCESS Linnaeus Ctr, S-10044 Stockholm, Sweden..
    Reaching a Quantum Consensus: Master Equations That Generate Symmetrization and Synchronization2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 2, p. 374-387Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose and study amaster-equation based approach to drive a quantum network with n qubits to a consensus (symmetric) state introduced by Mazzarella et al. The state evolution of the quantum network is described by a Lindblad master equation with the Lindblad terms generated by continuous-time swapping operators, which also introduce an underlying interaction graph. We establish a graphical method that bridges the proposed quantum consensus scheme and classical consensus dynamics by studying an induced graph (with 2(2n) nodes) of the quantum interaction graph (with n qubits). A fundamental connection is then shown that quantum consensus over the quantum graph is equivalent to componentwise classical consensus over the induced graph, which allows various existing works on classical consensus to be applicable to the quantum setting. Some basic scaling and structural properties of the quantum induced graph are established via combinatorial analysis. Necessary and sufficient conditions for exponential and asymptotic quantum consensus are obtained, respectively, for switching quantum interaction graphs. As a quantum analogue of classical synchronization of coupled oscillators, quantum synchronization conditions are also presented, in which the reduced states of all qubits tend to a common trajectory.

  • 120.
    Shi, Guodong
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hong, Yiguang
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Connectivity and set tracking of multi-agent systems guided by multiple moving leaders2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 3, p. 663-676Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate distributed multi-agent tracking of a convex set specified by multiple moving leaders with unmeasurable velocities. Various jointly connected interaction topologies of the follower agents with uncertainties are considered in the study of set tracking. Based on the connectivity of the time-varying multi-agent system, necessary and sufficient conditions are obtained for set input-to-state stability and set integral input-to-state stability for a nonlinear neighbor-based coordination rule with switching directed topologies. Conditions for asymptotic set tracking are also proposed with respect to the polytope spanned by the leaders.

  • 121.
    Shi, Guodong
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hong, Y.
    Reaching an optimal consensus: Dynamical systems that compute intersections of convex sets2013In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 58, no 3, p. 610-622Article in journal (Refereed)
    Abstract [en]

    In this paper, multi-agent systems minimizing a sum of objective functions, where each component is only known to a particular node, is considered for continuous-time dynamics with time-varying interconnection topologies. Assuming that each node can observe a convex solution set of its optimization component, and the intersection of all such sets is nonempty, the considered optimization problem is converted to an intersection computation problem. By a simple distributed control rule, the considered multi-agent system with continuous-time dynamics achieves not only a consensus, but also an optimal agreement within the optimal solution set of the overall optimization objective. Directed and bidirectional communications are studied, respectively, and connectivity conditions are given to ensure a global optimal consensus. In this way, the corresponding intersection computation problem is solved by the proposed decentralized continuoustime algorithm. We establish several important properties of the distance functions with respect to the global optimal solution set and a class of invariant sets with the help of convex and non-smooth analysis.

  • 122.
    Stankovic, Milos S.
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stipanovic, Dusan M.
    Department of Industrial and Enterprise Systems Engineering and the Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, Illinois, USA.
    Distributed Seeking of Nash Equilibria With Applications to Mobile Sensor Networks2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 4, p. 904-919Article in journal (Refereed)
    Abstract [en]

    We consider the problem of distributed convergenceto a Nash equilibrium in a noncooperative game where the playersgenerate their actions based only on online measurements oftheir individual cost functions, corrupted with additive measurementnoise. Exact analytical forms and/or parameters ofthe cost functions, as well as the current actions of the playersmay be unknown. Additionally, the players’ actions are subjectto linear dynamic constraints. We propose an algorithm basedon discrete-time stochastic extremum seeking using sinusoidalperturbations and prove its almost sure convergence to a Nashequilibrium. We show how the proposed algorithm can be appliedto solving coordination problems in mobile sensor networks,where motion dynamics of the players can be modeled as: 1) singleintegrators (velocity-actuated vehicles), 2) double integrators(force-actuated vehicles), and 3) unicycles (a kinematic modelwith nonholonomic constraints). Examples are given in which thecost functions are selected such that the problems of connectivitycontrol, formation control, rendezvous and coverage control aresolved in an adaptive and distributed way. The methodology isillustrated through simulations.

  • 123. Stankovic, M.S
    et al.
    Stankovic, S.S
    Johansson, Karl
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Blind Calibration in Lossy Sensor Networks via Output Synchronization2015In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 60, no 12, p. 3257-3262Article in journal (Refereed)
    Abstract [en]

    A novel distributed algorithm for blind macrocalibration of large sensor networks is introduced. The algorithm is in the form of a system of gradient-type recursions for estimating parameters of local sensor calibration functions. The method does not require any fusion center. The convergence analysis is based on diagonal dominance of the dynamical systems with block matrices. It is proved that the asymptotic consensus is achieved for all the equivalent sensor gains and offsets (in the mean square sense and with probability one) in lossy sensor networks with possible communication outages and additive communication noise. An illustrative simulation example is provided.

  • 124.
    Swindlehurst, A.
    et al.
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA..
    Roy, R.
    ArrayComm, Inc., Santa Clara, CA 95054 USA..
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kailath, T.
    Information Systems Lab, Stanford University, Stanford, CA 94305 USA..
    A subspace fitting method for identification of linear state-space models1995In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 40, no 2, p. 311-316Article in journal (Refereed)
    Abstract [en]

    A new method is presented for the identification of systems parameterized bylinear state-space models. The method relies on the concept of subspacefitting, wherein an input/output data model parameterized by the statematrices is found that best fits, in the least-squares sense, the dominantsubspace of the measured data. Some empirical results are included to illustrate the performance advantage of the algorithm compared to standard techniques

  • 125.
    Talebi Mazraeh Shahi, Mohammad Sadegh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Zou, Zhenhua
    Ericsson Res, SE-16483 Stockholm, Sweden..
    Combes, Richard
    Cent Supelec L2S, Telecommun Dept, F-91192 Gif Sur Yvette, France..
    Proutiere, Alexandre
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Stochastic Online Shortest Path Routing: The Value of Feedback2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 4, p. 915-930Article in journal (Refereed)
    Abstract [en]

    This paper studies online shortest path routing over multihop networks. Link costs or delays are time varying and modeled by independent and identically distributed random processes, whose parameters are initially unknown. The parameters, and hence the optimal path, can only be estimated by routing packets through the network and observing the realized delays. Our aim is to find a routing policy that minimizes the regret (the cumulative difference of expected delay) between the path chosen by the policy and the unknown optimal path. We formulate the problem as a combinatorial bandit optimization problem and consider several scenarios that differ in where routing decisions are made and in the information available when making the decisions. For each scenario, we derive a tight asymptotic lower bound on the regret that has to be satisfied by any online routing policy. Three algorithms, with a tradeoff between computational complexity and performance, are proposed. The regret upper bounds of these algorithms improve over those of the existing algorithms. We also assess numerically the performance of the proposed algorithms and compare it to that of existing algorithms.

  • 126.
    Tanaka, Takashi
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kim, Kwang-Ki K.
    Parrilo, Pablo A.
    Mitter, Sanjoy K.
    Semidefinite Programming Approach to Gaussian Sequential Rate-Distortion Trade-Offs2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 4, p. 1896-1910Article in journal (Refereed)
    Abstract [en]

    Sequential rate-distortion (SRD) theory provides a framework for studying the fundamental trade-off between data-rate and data-quality in real-time communication systems. In this paper, we consider the SRD problem for multi-dimensional time-varying Gauss-Markov processes under mean-square distortion criteria. We first revisit the sensor-estimator separation principle, which asserts that considered SRD problem is equivalent to a joint sensor and estimator design problem in which data-rate of the sensor output is minimized while the estimator's performance satisfies the distortion criteria. We then show that the optimal joint design can be performed by semidefinite programming. A semidefinite representation of the corresponding SRD function is obtained. Implications of the obtained result in the context of zero-delay source coding theory and applications to networked control theory are also discussed.

  • 127.
    Theodosis, Dionysios
    et al.
    Natl Tech Univ Athens, Dept Math, Athens 15780, Greece..
    Boskos, Dimitris
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Tsinias, John
    Natl Tech Univ Athens, Dept Math, Athens 15780, Greece..
    Observer Design for Triangular Systems Under Weak Observability Assumptions2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 12, p. 4156-4171Article in journal (Refereed)
    Abstract [en]

    This paper presents results on the solvability of the observer design problem for general nonlinear triangular systems with inputs, under weak observability assumptions. The local state estimation is exhibited by means of a delayed time-varying Luenberger-type system. In order to achieve the global estimation, a switching sequence of observers is designed.

  • 128. Thunberg, Johan
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Goncalves, Jorge
    Local Lyapunov Functions for Consensus in Switching Nonlinear Systems2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 12, p. 6466-6472Article in journal (Refereed)
    Abstract [en]

    This note presents two theorems on asymptotic state consensus of continuous time nonlinear multi-agent systems. The agents reside in Rm and have switching interconnection topologies. Both the first theorem, formulated in terms of the states of individual agents, and the second theorem, formulated in terms of the pairwise states for pairs of agents, can be interpreted as variants of Lyapunov's second method. The two theorems complement each other; the second provides stronger convergence results under weaker graph topology assumptions, whereas the first often can be applied in a wider context in terms of the structure of the right-hand sides of the systems. The second theorem also sheds some new light on well-known results for consensus of nonlinear systems where the right-hand sides of the agents' dynamics are convex combinations of directions to neighboring agents. For such systems, instead of proving consensus by using the theory of contracting convex sets, a local quadratic Lyapunov function can be used.

  • 129. Tzortzis, Ioannis
    et al.
    Charalambous, Charalambos D.
    Charalambous, Themistoklis
    Hadjicostis, Christoforos N.
    Johansson, Mikael
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Approximation of Markov Processes by Lower Dimensional Processes via Total Variation Metrics2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 3, p. 1030-1045Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to approximate a Finite-State Markov (FSM) process by another process defined on a lower dimensional state space, called the approximating process, with respect to a total variation distance fidelity criterion. The approximation problem is formulated as an optimization problem using two different approaches. The first approach is based on approximating the transition probability matrix of the FSM process by a lower-dimensional transition probability matrix, resulting in an approximating process which is a Finite-State Hidden Markov (FSHM) process. The second approach is based on approximating the invariant probability vector of the original FSM process by another invariant probability vector defined on a lower-dimensional state space. Going a step further, a method is proposed based on optimizing a Kullback-Leibler divergence to approximate the FSHM processes by FSM processes. The solutions of these optimization problems are described by optimal partition functions which aggregate the states of the FSM process via a corresponding water-filling solution, resulting in lower-dimensional approximating processes which are FSHM or FSM processes. Throughout the paper, the theoretical results are justified by illustrative examples that demonstrate our proposed methodology.

  • 130.
    Varagnolo, Damiano
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pillonetto, Gianluigi
    Schenato, Luca
    Univ Padua, Dept Informat Engn, I-35131 Padua, Italy.
    Distributed Cardinality Estimation in Anonymous Networks2013In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 3, p. 645-659Article in journal (Refereed)
    Abstract [en]

    We consider estimation of network cardinality by distributed anonymous strategies relying on statistical inference methods. In particular, we focus on the relative Mean Square Error (MSE) of Maximum Likelihood (ML) estimators based on either the maximum or the average of M-dimensional vectors randomly generated at each node. In the case of continuous probability distributions, we show that the relative MSE achieved by the max-based strategy decreases as, independently of the used distribution, while that of the average-based estimator scales approximately as. We then introduce a novel strategy based on the average of M-dimensional vectors locally generated from Bernoulli random variables. In this case, the ML estimator, which is the Least Common Multiple (LCM) of the denominators of the irreducible fractions corresponding to the elements of the average vector, leads to an MSE which goes exponentially to zero as increases. We then discuss the effects of finite-precision arithmetics in practical dynamic implementations. Numerical experiments reveal that the MSE of the strategy based on Bernoulli trials is two order of magnitude smaller than that based on continuous random variables, at a price of one order of magnitude slower convergence time.

  • 131.
    Wahlberg, Bo
    KTH, Superseded Departments, Signals, Sensors and Systems.
    System identification using Kautz models1994In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 39, no 6, p. 1276-1282Article in journal (Refereed)
    Abstract [en]

    In this paper, the problem of approximating a linear time-invariant stable system by a finite weighted sum of given exponentials is considered. System identification schemes using Laguerre models are extended and generalized to Kautz models, which correspond to representations using several different possible complex exponentials. In particular, linear regression methods to estimate this sort of model from measured data are analyzed. The advantages of the proposed approach are the simplicity of the resulting identification scheme and the capability of modeling resonant systems using few parameters. The subsequent analysis is based on the result that the corresponding linear regression normal equations have a block Toeplitz structure. Several results on transfer function estimation are extended to discrete Kautz models, for example, asymptotic frequency domain variance expressions.

  • 132.
    Wahlberg, Bo
    Department of Electrical Engineering, Linköping University.
    System identification using Laguerre models1991In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 36, no 5, p. 551-562Article in journal (Refereed)
    Abstract [en]

    The traditional approach of expanding transfer functions and noise models in the delay operator to obtain linear-in-the-parameters predictor models leads to approximations of very high order in cases of rapid sampling and/or dispersion in time constants. By using prior information about the time constants of the system more appropriate expansions, related to Laguerre networks, are introduced and analyzed. It is shown that the model order can be reduced, compared to ARX (FIR, AR) modeling, by using Laguerre models. Furthermore, the numerical accuracy of the corresponding linear regression estimation problem is improved by a suitable choice of the Laguerre parameter. Consistency (error bounds), persistance of excitation conditions, and asymptotic statistical properties are investigated. This analysis is based on the result that the covariance matrix of the regression vector of a Laguerre model has a Toeplitz structure.

  • 133.
    Wahlberg, Bo
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stoica, P.
    Uppsala University.
    On the Performance of Optimal Input Signals for Frequency Response Estimation2012In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 57, no 5, p. 766-771Article in journal (Refereed)
    Abstract [en]

    We consider the problem of minimum-variance excitation design for frequency response estimation based on finite impulse response (FIR) and output error (OE) models. The objective is to minimize the power of the input signal to be used in the system identification experiment subject to a model accuracy constraint. For FIR and OE models this leads to a finite dimensional semi-definite programming optimization problem. We study, in detail, how to apply this approach to the estimation of the frequency response at a given frequency, . The first case concerns minimizing the asymptotic variance of the estimated frequency response based on an FIR model estimate. We compare the optimal input signal with a sinusoidal signal with frequency that gives the same model accuracy, and show that the input power can, at best, be reduced by a factor of two when using the optimal input signal. Conditions are given under which the sinusoidal signal is optimal, and it is shown that this is a common case for higher order FIR models. Next, we study FIR model based estimation of the absolute value and phase of the frequency response at a given frequency, . We derive the corresponding optimal input signals and compare their performances with that of a sinusoidal input signal with frequency . The relative reduction of input power when using the optimal solution is at best a factor of two. Finally, we discuss how to extend the FIR results to OE system identification by using an input parametrization proposed by Stoica and Söderström (1982).

  • 134.
    Wahlberg, Bo
    et al.
    Department of Electrical Engineering, Linköping University.
    Ljung, Lennart
    Department of Electrical Engineering, Linköping University.
    Design Variables For Bias Distribution In Transfer Function Eestimation1986In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, ISSN 0018-9286, Vol. AC-31, no 2, p. 134-144Article in journal (Refereed)
    Abstract [en]

    Estimation of transfer functions of linear systems is one of the most common system identification problems. Several different design variables, chosen by the user for the identification procedure, affect the properties of the resulting estimate. The way in which the choices of prefilters, noise models, sampling interval, and prediction horizon (the use of k-step ahead prediction methods) influence the estimate is discussed. An important aspect is that the true system is not assumed to be exactly represented within the chosen model set. The estimate will thus be biased. It is shown how the distribution of bias in the frequency domain is governed by a weighting function, which emphasizes different frequency bands. The weighting function, in turn, is a result of the previously listed design variables. It is shown that the common least-squares method has a tendency to emphasize high frequencies and that this can be counteracted by prefiltering. It is also shown that, asymptotically, it is only the prediction horizon itself, and not how it is split up into sampling interval times number of predicted sampling instants, that affects this weighting function.

  • 135.
    Wahlberg, Bo
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ljung, Lennart
    Department of Electrical Engineering, Linköping University.
    Hard frequency-domain model error bounds from least-squares like identification techniques1992In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 37, no 7, p. 900-912Article in journal (Refereed)
    Abstract [en]

    The problem of deriving so-called hard-error bounds for estimated transfer functions is addressed. A hard bound is one that is sure to be satisfied, i.e., the true system Nyquist plot will be confined with certainty to a given region, provided that the underlying assumptions are satisfied. By blending a priori knowledge and information obtained from measured data, it is shown how the uncertainty of transfer function estimates can be quantified. The emphasis is on errors due to model mismatch. The effects of unmodeled dynamics can be considered as bounded disturbances. Hence, techniques from set membership identification can be applied to this problem. The approach taken corresponds to weighted least-squares estimation, and provides hard frequency-domain transfer function error bounds. The main assumptions used in the current contribution are: that the measurement errors are bounded, that the true system is indeed linear with a certain degree of stability, and that there is some knowledge about the shape of the true frequency response.

  • 136.
    Weeraddana, Pradeep Chathuranga
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Athanasiou, Georgios
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Jakobsson, Martin
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Baras, John S.
    University of Maryland.
    Per-se Privacy Preserving Distributed OptimizationIn: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523Article in journal (Other academic)
    Abstract [en]

    Ensuring privacy in distributed optimization is essential in many contexts, such as healthcare data,banks, e-commerce, government services, and social networks. In these contexts, it is common thatdifferent parties coordinate to solve a specific optimization problem whose data is dispersed amongthe parties, where no entity wants to publish its data during the solution procedure. Addressing theseproblems falls under the umbrella of well-knownsecured multiparty computation(SMC). Existingapproaches for SMC are mostly based on cryptography. Surprisingly, little attention has been devotedthus far to develop non-cryptographic approaches, that can be much more efficient. In this paper,we investigate alternative non-cryptographic methods based onmathematical optimization techniques.First, aunified frameworkto encapsulate existing non-cryptographic methods, which rely algebraictransformations to disguise sensitive problem data, is developed. The proposed framework capitalizes onkey optimization techniques, such aschange of variablesandtransformation of objective and constraintfunctions, for equivalent problem formation. Moreover, the privacy preserving properties that are inherentin the mathematical optimization techniques, including classical decomposition methods (e.g., primal anddual decomposition), and state-of-the-art methods, such as alternating direction method of multipliersare investigated. A general definition for quantifying the privacy in the context of non-cryptographicapproaches is proposed. A number of examples are provided to illustrate the importance of our proposedalgorithms. It is concluded that the theory is in its infancy and that huge benefits can be achieved by asubstantial development.

  • 137.
    Wei, Jieqiang
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Zhang, Silun
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Adaldo, Antonio
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Johan, Thunberg
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Finite-time attitude synchronization with distributed discontinuous protocols2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 10, p. 3608-3615Article in journal (Refereed)
    Abstract [en]

    The finite-time attitude synchronization problem is considered in this paper, where the rotation of each rigid body is expressed using the axis-angle representation. Two discontinuous and distributed controllers using the vectorized signum function are proposed, which guarantee almost global and local convergence, respectively. Filippov solutions and non-smooth analysis techniques are adopted to handle the discontinuities. Sufficient conditions are provided to guarantee finite-time convergence and boundedness of the solutions. Simulation examples are provided to verify the performances of the control protocols designed in this paper.

  • 138.
    Wiese, Moritz
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Papadimitratos, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Sandberg, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Skoglund, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Secure Estimation and Zero-Error Secrecy Capacity2019In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, no 3, p. 1047-1062Article in journal (Refereed)
    Abstract [en]

    We study the problem of securely estimating the states of an unstable dynamical system subject to non-stochastic disturbances. The estimator obtains all its information through an uncertain channel, which is subject to nonstochastic disturbances as well, and an eavesdropper obtains a disturbed version of the channel inputs through a second uncertain channel. An encoder observes and block encodes the states in such a way that, upon sending the generated codeword, the estimator's error is bounded and a security criterion is satisfied, thereby ensuring that the eavesdropper obtains as little state information as possible. Two security criteria are considered and discussed with the help of a numerical example. A sufficient condition on the uncertain wiretap channel, i.e., the pair formed by the uncertain channel from the encoder to the estimator and the uncertain channel from the encoder to the eavesdropper is derived, which ensures that a bounded estimation error and security are achieved. This condition is also shown to be necessary for a subclass of uncertain wiretap channels. To formulate the condition, the zero-error secrecy capacity of uncertain wiretap channels is introduced, i.e., the maximal rate at which data can be transmitted from the encoder to the estimator in such a way that the eavesdropper is unable to reconstruct the transmitted data. Finally, the zero-error secrecy capacity of uncertain wiretap channels is studied.

  • 139.
    Witrant, Emmanuel
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Canudas-de-Wit, Carlos
    Georges, Didier
    Alamir, Mazen
    Remote stabilization via communication networks with a distributed control law2007In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 52, no 8, p. 1480-1485Article in journal (Refereed)
    Abstract [en]

    In this note, we investigate the problem of remote stabilization via communication networks involving some time-varying delays of Known average dynamics. This problem arises when the control law is remotely implemented and leads to the problem of stabilizing an open-loop unstable system with time-varying delay. We use a time-varying horizon predictor to design a stabilizing control law that sets the poles of the closed-loop system. The computation of the horizon of the predictor is investigated and the proposed control law explicitly takes into account an estimation of the average delay dynamics. The resulting closed loop system robustness with respect to some uncertainties on the delay estimation is also considered. Simulation results are finally presented.

  • 140. Wu, Junfeng
    et al.
    Jia, Qing-Shan
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shi, Ling
    Event-Based Sensor Data Scheduling: Trade-Off Between Communication Rate and Estimation Quality2013In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 58, no 4, p. 1041-1046Article in journal (Refereed)
    Abstract [en]

    We consider sensor data scheduling for remote state estimation. Due to constrained communication energy and bandwidth, a sensor needs to decide whether it should send the measurement to a remote estimator for further processing. We propose an event-based sensor data scheduler for linear systems and derive the corresponding minimum squared error estimator. By selecting an appropriate eventtriggering threshold, we illustrate how to achieve a desired balance between the sensor-to-estimator communication rate and the estimation quality. Simulation examples are provided to demonstrate the theory.

  • 141. Wu, Junfeng
    et al.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shi, Ling
    A Stochastic Online Sensor Scheduler for Remote State Estimation With Time-Out Condition2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 11, p. 3110-3116Article in journal (Refereed)
    Abstract [en]

    This technical note considers remote state estimation subject to limited sensor-estimator communication rate. We propose a stochastic online sensor scheduler for remote state estimation with time-out condition. The decision rule under which the sensor sends data is based on its measurements and a finite-state holding time between the present and the most recent sensor-to-estimator communication instance. This decision process is formulated as an optimization problem, relaxed and solved using generalized geometric programming optimization techniques with a low computational complexity. Moreover, the proposed scheduler is easy to execute, and provides a guaranteed performance which is shown to outperform the optimal offline scheduler. Numerical examples are provided to illustrate the proposed scheduler.

  • 142.
    Wu, Junfeng
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Shi, Guodong
    Australian Natl Univ, Res Sch Engn, Canberra, ACT 0200, Australia..
    Anderson, Brian D. O.
    Australian Natl Univ, Res Sch Engn, Canberra, ACT 0200, Australia..
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Kalman Filtering Over Gilbert-Elliott Channels: Stability Conditions and Critical Curve2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 4, p. 1003-1017Article in journal (Refereed)
    Abstract [en]

    This paper investigates the stability of Kalman filtering over Gilbert-Elliott channels where random packet drops follow a time-homogeneous two-state Markov chain whose state transition is determined by a pair of failure and recovery rates. First of all, we establish a relaxed condition guaranteeing peak-covariance stability described by an inequality in terms of the spectral radius of the system matrix and transition probabilities of the Markov chain. We further show that the condition can be interpreted using a linear matrix inequality feasibility problem. Next, we prove that the peak-covariance stability implies mean-square stability, if the system matrix has no defective eigenvalues on the unit circle. This connection between the two stability notions holds for any random packet drop process. We prove that there exists a critical curve in the failure-recovery rate plane, below which the Kalman filter is mean-square stable and no longer mean-square stable above. Finally, a lower bound for this critical failure rate is obtained making use of the relationship we establish between the two stability criteria, based on an approximate relaxation of the system matrix.

  • 143.
    Xia, Weiguo
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cao, Ming
    Sarymsakov Matrices and Asynchronous Implementation of Distributed Coordination Algorithms2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 8, p. 2228-2233Article in journal (Refereed)
    Abstract [en]

    We provide new insight into the somewhat obscure definition of the Sarymsakov class of stochastic matrices and use it to construct a new necessary and sufficient condition for the convergence of products of stochastic matrices. Such convergence result is critical in establishing the effectiveness of distributed coordination algorithms for multi-agent systems and enables us to investigate a specific coordination task with asynchronous update events. The set of scrambling stochastic matrices, a subclass of the Sarymsakov class, is utilized to establish the convergence of the agents' states even when there is no common clock for the agents to synchronize their update actions.

  • 144.
    Xia, Weiguo
    et al.
    Dalian Univ Technol, Sch Control Sci & Engn, Dalian 116023, Peoples R China..
    Shi, Guodong
    Univ Sydney, Sch Aerosp Mech & Mechatron Engn, Australian Ctr Field Robot, Sydney, NSW 2008, Australia.;Australian Natl Univ, Res Sch Engin, Canberra, ACT 0200, Australia..
    Meng, Ziyang
    Tsinghua Univ, Dept Precis Instrument, State Key Lab Precis Measurement Technol & Instru, Beijing 100084, Peoples R China..
    Cao, Ming
    Univ Groningen, Engn & Technol Inst Groningen, Fac Sci & Engn, NL-9712 Groningen, Netherlands..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Persis en Flows in Deterministic Chains2019In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, no 7, p. 2766-2781Article in journal (Refereed)
    Abstract [en]

    This paper studies, the role of persistent flows in the convergence of infinite backward products of stochastic matrices of deterministic chains over networks with nonreciprocal interactions between agents. An arc describing the interaction strength between two agents is said to be persistent if its weight function has an infinite l(1) norm; convergence of the infinite backward products to a rank-one matrix of a deterministic chain of stochastic matrices is equivalent to achieving consensus at the node states. We discuss two balance conditions on the interactions between agents, which generalize the arc-balance and cut-balance conditions in the literature, respectively. The proposed conditions require that such a balance should be satisfied over each time window of a fixed length instead of at each time instant. We prove that in both cases global consensus is reached if and only if the persistent graph, which consists of all the persistent arcs, contains a directed spanning tree. The convergence rates of the system to consensus are also provided in terms of the interactions between agents having taken place. The results are obtained under a weak condition without assuming the existence of a positive lower bound of all the nonzero weights of arcs and are compared with the existing results. Illustrative examples are provided to validate the results and show the critical importance of the nontrivial lower boundedness of the self-confidence of the agents.

  • 145. Yang, T.
    et al.
    Meng, Z.
    Shi, G.
    Hong, Y.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Network synchronization with nonlinear dynamics and switching interactions2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 10, p. 3103-3108, article id 7317753Article in journal (Refereed)
    Abstract [en]

    This technical note considers the synchronization problem for networks of coupled nonlinear dynamical systems under switching communication topologies. Two types of nonlinear agent dynamics are considered. The first one is non-expansive dynamics [stable dynamics with a convex Lyapunov function φ(·)] and the second one is dynamics that satisfies a global Lipschitz condition. For the non-expansive case, we show that various forms of joint connectivity for communication graphs are sufficient for networks to achieve global asymptotic φ-synchronization. We also show that φ-synchronization leads to state synchronization provided that certain additional conditions are satisfied. For the globally Lipschitz case, unlike the non-expansive case, joint connectivity alone is not sufficient for achieving synchronization. A sufficient condition for reaching global exponential synchronization is established in terms of the relationship between the global Lipschitz constant and the network parameters. © 2015 IEEE.

  • 146.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Liu, Kun
    Beijing Inst Technol, Sch Automat, Beijing 100081, Peoples R China..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Dynamic Event-Triggered and Self-Triggered Control for Multi-agent Systems2019In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, no 8, p. 3300-3307Article in journal (Refereed)
    Abstract [en]

    We propose two novel dynamic event-triggered control laws to solve the average consensus problem for first-order continuous-time multiagent systems over undirected graphs. Compared with the most existing triggering laws, the proposed laws involve internal dynamic variables, which play an essential role in guaranteeing that the triggering time sequence does not exhibit Zeno behavior. Moreover, some existing triggering laws are special cases of ours. For the proposed self-triggered algorithm, continuous agent listening is avoided as each agent predicts its next triggering time and broadcasts it to its neighbors at the current triggering time. Thus, each agent only needs to sense and broadcast at its triggering times, and to listen to and receive incoming information from its neighbors at their triggering times. It is proved that the proposed triggering laws make the state of each agent converge exponentially to the average of the agents' initial states if and only if the underlying graph is connected. Numerical simulations are provided to illustrate the effectiveness of the theoretical results.

  • 147.
    Yu, Pian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Distributed Event-Triggered Communication and Control of Linear Multiagent Systems Under Tactile Communication2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 11, p. 3979-3985Article in journal (Refereed)
    Abstract [en]

    This note is concerned with the consensus of linear multiagent systems under tactile communication. Motivated by the emerging tactile communication technology where extremely low latency has to be supported, a distributed event-triggered communication and control scheme is proposed for the data reduction of each agent. First, an event-triggered data reduction scheme is designed for the communication between neighbors. Under such a communication scheme, a distributed event-triggered output feedback controller is further implemented for each agent, which is updated asynchronously with the communication action. It is proven that the consensus of the underlying multiagent systems is achieved asymptotically. Furthermore, it is shown that the proposed communication and control strategy fulfils the reduction of both the frequency of communication and controller updates as well as excluding Zeno behavior. A numerical example is given to illustrate the effectiveness of the proposed control strategy.

  • 148.
    Zaidi, Ali Abbas
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Serdar, Yuksel
    Mathematics and Statistics, Queen's University, Canada.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Stabilization of Linear Systems Over Gaussian Networks2014In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, no 9, p. 2369-2384Article in journal (Refereed)
  • 149. Zamani, Mohsen
    et al.
    Bottegal, Giulio
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Anderson, Brian D. O.
    On the Zero-Freeness of Tall Multirate Linear Systems2016In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 61, no 11, p. 3606-3611Article in journal (Refereed)
    Abstract [en]

    In this technical note, tall discrete-time linear systems with multirate outputs are studied. In particular, we focus on their zeros. In systems and control literature zeros of multirate systems are defined as those of their corresponding time-invariant systems obtained through blocking of the original multirate systems. We assume that blocked systems are tall, i.e., have more outputs than inputs. It is demonstrated that, for generic choice of the parameter matrices, linear systems with multirate outputs generically have no finite nonzero zeros. However, they may have zeros at the origin or at infinity depending on the choice of blocking delay and the input, state and output dimensions.

  • 150.
    Zhang, Huimin
    et al.
    School of Electro-Mechanical Engineering, Xidian University, Xi'an China.
    Feng, Lei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Li, Zhiwu
    School of Electro-Mechnical Engineering, Xidian University, Xi'an China.
    A learning-based synthesis approach to the supremal nonblocking supervisor of discrete-event systems2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 10, p. 3345-3360Article in journal (Refereed)
    Abstract [en]

    The paper presents a novel approach to synthesize supremal nonblocking supervisors of discrete-event systems (DES), when the automaton models of specifications are not available. Extending the L* learning algorithm, an S* algorithm is developed to infer a tentatively correct supervisor. If the tentatively correct supervisor is nonblocking, it is indeed the supremal nonblocking supervisor with respect to the plant and specifications. Otherwise, the blocking automaton is regarded as a new plant, and the specification is the nonblocking property. Then, the supremal nonblocking supervisor with respect to the new problem is computed using supervisory control theory of DES. Two simplification rules are introduced to the S* algorithm to decrease the computational cost. Finally, the S* algorithm is implemented based on the LearnLib framework, and experiments are performed to verify the proposed approach.

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