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147
Control and Communication Challenges in Networked Realtime Systems
, 2007
"... A current survey of the emerging field of networked control systems is provided. The aim is to introduce the fundamental issues involved in designing successful networked control systems, to provide a snapshot assessment of the current state of research in the field, to suggest useful future researc ..."
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Cited by 62 (4 self)
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A current survey of the emerging field of networked control systems is provided. The aim is to introduce the fundamental issues involved in designing successful networked control systems, to provide a snapshot assessment of the current state of research in the field, to suggest useful future research directions, and to provide a broad perspective on recent fundamental results. Reflecting the goals of the Special Issue itself, this paper surveys relevant work from the areas of systems and control, signal processing, detection and estimation, data fusion, and distributed systems. We discuss appropriate network architectures, topics such as coding for
Safe and secure networked control systems under denial ofservice attacks
 In Hybrid systems: Computation and Control
, 2009
"... Abstract. We consider the problem of security constrained optimal control for discretetime, linear dynamical systems in which control and measurement packets are transmitted over a communication network. The packets may be jammed or compromised by a malicious adversary. For a class of denialofs ..."
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Cited by 57 (3 self)
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Abstract. We consider the problem of security constrained optimal control for discretetime, linear dynamical systems in which control and measurement packets are transmitted over a communication network. The packets may be jammed or compromised by a malicious adversary. For a class of denialofservice (DoS) attack models, the goal is to find an (optimal) causal feedback controller that minimizes a given objective function subject to safety and power constraints. We present a semidefinite programming based solution for solving this problem. Our analysis also presents insights on the effect of attack models on solution of the optimal control problem. 1
Data Transmission over Networks for Estimation and Control
"... We consider the problem of controlling a linear time invariant process when the controller is located at a location remote from where the sensor measurements are being generated. The communication from the sensor to the controller is supported by a communication network with arbitrary topology compo ..."
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Cited by 45 (9 self)
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We consider the problem of controlling a linear time invariant process when the controller is located at a location remote from where the sensor measurements are being generated. The communication from the sensor to the controller is supported by a communication network with arbitrary topology composed of analog erasure channels. Using a separation principle, we prove that the optimal LQG controller consists of an LQ optimal regulator along with an estimator that estimates the state of the process across the communication network mentioned above. We then determine the optimal information processing strategy that should be followed by each node in the network so that the estimator is able to compute the best possible estimate in the minimum mean squared error sense. The algorithm is optimal for any packetdropping process and at every time step, even though it is recursive and hence requires a constant amount of memory, processing and transmission at every node in the network per time step. For the case when the packet drop processes are memoryless and independent across links, we analyze the stability properties and the performance of the closed loop system. The algorithm is an attempt to escape the more commonly used viewpoint of treating a network of communication links as a single endtoend link with the probability of successful transmission determined by some measure of the reliability of the network. I.
Data rate theorem for stabilization over timevarying feedback channels
 IEEE TRANSACTIONS ON AUTOMATIC CONTROL
, 2009
"... A data rate theorem for stabilization of a linear, discretetime, dynamical system with arbitrarily large disturbances, over a ratelimited, timevarying communication channel is presented. Necessary and sufficient conditions for stabilization are derived, their implications and relationships with r ..."
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Cited by 41 (5 self)
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A data rate theorem for stabilization of a linear, discretetime, dynamical system with arbitrarily large disturbances, over a ratelimited, timevarying communication channel is presented. Necessary and sufficient conditions for stabilization are derived, their implications and relationships with related results in the literature are discussed. The proof techniques rely on both informationtheoretic and controltheoretic tools.
Secure control: Towards survivable cyberphysical systems
 in First International Workshop on CyberPhysical Systems (WCPS2008
, 2008
"... In this position paper we investigate the security of cyberphysical systems. We (1) identify and define the problem of secure control, (2) investigate the defenses that information security and control theory can provide, and (3) propose a set of challenges that need to be addressed to improve the s ..."
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Cited by 39 (1 self)
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In this position paper we investigate the security of cyberphysical systems. We (1) identify and define the problem of secure control, (2) investigate the defenses that information security and control theory can provide, and (3) propose a set of challenges that need to be addressed to improve the survivability of cyberphysical systems. 1
For the grid and through the grid: The role of power line communications in the smart grid,” to appear
 in Proceedings of the IEEE, 2011. [Online]. Available: http://arxiv.org/abs/1010.1973
"... is to address this important question. To do so we provide an overview of what PLC can deliver today by surveying its history and describing the most recent technological advances in the area. We then address Smart Grid applications as instances of sensor networking and network control problems and ..."
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Cited by 36 (1 self)
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is to address this important question. To do so we provide an overview of what PLC can deliver today by surveying its history and describing the most recent technological advances in the area. We then address Smart Grid applications as instances of sensor networking and network control problems and discuss the main conclusion one can draw from the literature on these subjects. The application scenario of PLC within the Smart Grid is then analyzed in detail. Since a necessary ingredient of network planning is modeling, we also discuss two aspects of engineering modeling that relate to our question. The first aspect is modeling the PLC channel through fading models. The second aspect we review is the Smart Grid control and traffic modeling problem which allows us to achieve a better understanding of the communications requirements. Finally, this paper reports recent studies on the electrical and topological properties of a sample power distribution network. Power grid topological studies are very important for PLC networking as the power grid is not only the information source but also the information delivery system a unique feature when PLC is used for the Smart Grid. Index Terms—Smart grid, power grid, power line communications, power line channel, cyberphysical systems. I.
The Wireless Control Network: A New Approach for Control Over Networks
, 2011
"... We present a method to stabilize a plant with a network of resource constrained wireless nodes. As opposed to traditional networked control schemes where the nodes simply route information to and from a dedicated controller (perhaps performing some encoding along the way), our approach treats the ne ..."
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Cited by 29 (6 self)
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We present a method to stabilize a plant with a network of resource constrained wireless nodes. As opposed to traditional networked control schemes where the nodes simply route information to and from a dedicated controller (perhaps performing some encoding along the way), our approach treats the network itself as the controller. Specifically, we formulate a strategy for each node in the network to follow, where at each timestep, each node updates its internal state to be a linear combination of the states of the nodes in its neighborhood. We show that this causes the entire network to behave as a linear dynamical system, with sparsity constraints imposed by the network topology. We provide a numerical design procedure to determine appropriate linear combinations to be applied by each node so that the transmissions of the nodes closest to the actuators will stabilize the plant. We also show how our design procedure can be modified to maintain mean square stability under packet drops in the network, and presen ta distributed scheme that can handle node failures while preserving stability. We call this architecture a Wireless Control Network, and show that it introduces very low computational and communication overhead to the nodes in the network, allows the use of simple transmission scheduling algorithms, and enables compositional design (where the existing wireless control infrastructure can be easily extended to handle new plants that are brought online in the vicinity of the network).
Secure control against replay attacks
 Proceedings of the 47th annual Allerton conference on Communication, control, and computing
, 2009
"... This paper analyzes the effect of replay attacks on a control system. We assume an attacker wishes to disrupt the operation of a control system in steady state. In order to inject an exogenous control input without being detected the attacker will hijack the sensors, observe and record their reading ..."
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Cited by 23 (1 self)
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This paper analyzes the effect of replay attacks on a control system. We assume an attacker wishes to disrupt the operation of a control system in steady state. In order to inject an exogenous control input without being detected the attacker will hijack the sensors, observe and record their readings for a certain amount of time and repeat them afterwards while carrying out his attack. This is a very common and natural attack (we have seen numerous times intruders recording and replaying security videos while performing their attack undisturbed) for an attacker who does not know the dynamics of the system but is aware of the fact that the system itself is expected to be in steady state for the duration of the attack. We assume the control system to be a discrete time linear time invariant gaussian system applying an infinite horizon Linear Quadratic Gaussian (LQG) controller. We also assume that the system is equipped with a χ 2 failure detector. The main contributions of the paper, beyond the novelty of the problem formulation, consist in 1) providing conditions on the feasibility of the replay attack on the aforementioned system and 2) proposing a countermeasure that guarantees a desired probability of detection (with a fixed false alarm rate) by trading off either detection delay or LQG performance, either by decreasing control accuracy or increasing control effort. 1.
Control over noisy forward and reverse channels
 IEEE Trans. Automatic Control
"... Abstract—We consider the problem of remotely controlling a continuoustime linear timeinvariant system driven by Brownian motion process, when communication takes place over noisy memoryless discrete or continuousalphabet channels. What makes this class of remote control problems different from m ..."
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Cited by 23 (10 self)
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Abstract—We consider the problem of remotely controlling a continuoustime linear timeinvariant system driven by Brownian motion process, when communication takes place over noisy memoryless discrete or continuousalphabet channels. What makes this class of remote control problems different from most of the previously studied models is the presence of noise in both the forward channel (connecting sensors to the controller) and the reverse channel (connecting the controller to the plant). For stability of the closedloop system, we look for the existence of an invariant distribution for the state, for which we show that it is necessary that the entire control space and the state space be encoded, and that the reverse channel be at least as reliable as the forward channel. We obtain necessary conditions and sufficient conditions on the channels and the controllers for stabilizability. Using properties of the underlying sampled Markov chain, we show that under variablelength coding and some realistic channel conditions, stability can be achieved over discretealphabet channels even if the entire state and control spaces are to be encoded and the number of bits that can be transmitted per unit time is strictly bounded. For control over continuousalphabet channels, however, a variable rate scheme is not necessary. We also show that memoryless policies are rateefficient for Gaussian channels. Index Terms—Information theory, networked control systems, stochastic control, stochastic stability.
A Framework for Control System Design Subject to Average DataRate Constraints
"... This paper studies discretetime control systems subject to average datarate limits. We focus on a situation where a noisy linear system has been designed assuming transparent feedback and, due to implementation constraints, a sourcecoding scheme (with unity signal transfer function) has to be dep ..."
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Cited by 20 (10 self)
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This paper studies discretetime control systems subject to average datarate limits. We focus on a situation where a noisy linear system has been designed assuming transparent feedback and, due to implementation constraints, a sourcecoding scheme (with unity signal transfer function) has to be deployed in the feedback path. For this situation, and by focusing on a class of sourcecoding schemes built around entropy coded dithered quantizers, we develop a framework to deal with average datarate constraints in a tractable manner that combines ideas from both information and control theories. As an illustration of the uses of our framework, we apply it to study the interplay between stability and average datarates in the considered architecture. It is shown that the proposed class of coding schemes can achieve mean square stability at average datarates that are, at most, 1.254 bits per sample away from the absolute minimum rate for stability established by Nair and Evans. This rate penalty is compensated by the simplicity of our approach.