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18
On the pathloss attenuation regime for positive cost and linear scaling of transport capacity in wireless networks
 IEEE Trans. Inf. Theory
, 2006
"... Abstract — Wireless networks with a minimum internode separation distance are studied where the signal attenuation grows in 1 magnitude as ρδ with distance ρ. Two performance measures of wireless networks are analyzed. The transport capacity is the supremum of the total distancerate products that ..."
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Cited by 46 (6 self)
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Abstract — Wireless networks with a minimum internode separation distance are studied where the signal attenuation grows in 1 magnitude as ρδ with distance ρ. Two performance measures of wireless networks are analyzed. The transport capacity is the supremum of the total distancerate products that can be supported by the network. The energy cost of information transport is the infimum of the ratio of the transmission energies used by all the nodes to the number of bitmeters of information thereby transported. If the phases of the attenuations between node pairs are uniformly and independently distributed, it is shown that the expected transport capacity is upper bounded by a multiple of the total of the transmission powers of all the nodes, whenever δ> 2 for twodimensional networks or δ> 5 for onedimensional 4 networks, even if all the nodes have full knowledge of all the phases, i.e., full channel state information. If all nodes have an individual power constraint, the expected transport capacity grows at most linearly in the number of nodes due to the linear growth of the total power. This establishes the best case order of expected transport capacity for these ranges of pathloss exponents since linear scaling is also feasible. If the phases of the attenuations are arbitrary, it is shown that the transport capacity is upper bounded by a multiple of the total transmission power whenever δ> 5 for twodimensional 2 networks or δ> 3 for onedimensional networks, even if all the 2 nodes have full channel state information. This shows that there is indeed a positive energy cost which is no less than the reciprocal of the above multiplicative constant. It narrows the transition regime where the behavior is still open, since it is known that when δ < 3 for twodimensional networks, or δ < 1 for one2 dimensional networks, the transport capacity cannot generally be bounded by any multiple of the total transmit power. Index Terms — Ad hoc networks, capacity of wireless networks, cutset bound, maxflow mincut bound, multiuser information theory, network information theory, scaling laws, transport capacity, wireless networks. I.
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 20 (3 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.
A MIDDLEWARE FRAMEWORK FOR NETWORKED CONTROL SYSTEMS
, 2005
"... Networked control systems could possibly constitute the next logical step in the evolution of control, leading to the convergence of control with communication and computing. A central challenge is that traditional digital control methods cannot be directly applied to such systems. However, if appro ..."
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Cited by 7 (2 self)
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Networked control systems could possibly constitute the next logical step in the evolution of control, leading to the convergence of control with communication and computing. A central challenge is that traditional digital control methods cannot be directly applied to such systems. However, if appropriate system abstractions can be engineered, then such methods and theory can still be utilized. Our thesis is that a well designed middleware framework can indeed manufacture such an abstraction of virtual collocation, and thereby, propel the further proliferation of networked control systems. In this thesis, we present such a middleware framework for networked control systems. Central to this framework is Etherware, a message oriented component middleware for such systems. We begin with a detailed description of the design and architecture of Etherware, and illustrate Etherware based development of networked control systems through a fairly complex traffic control testbed application. Building on the middleware, we address
A new feedback control mechanism for error correction in packetswitched networks
 in 44th IEEE CDC  ECC
, 2005
"... Abstract — Error correction mechanisms enable control and other realtime applications to be executed over unreliable packetswitched networks. By adding carefully adjusted redundancy to transmitted data at the sender, it is possible to recover lost data at the receiver and thereby improve effective ..."
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Cited by 6 (2 self)
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Abstract — Error correction mechanisms enable control and other realtime applications to be executed over unreliable packetswitched networks. By adding carefully adjusted redundancy to transmitted data at the sender, it is possible to recover lost data at the receiver and thereby improve effective throughput. We describe simple models for packet loss, which allow us to find the optimal redundancy as a function of packet loss probability. Two feedforward control mechanisms based on the packet loss probability are presented: one that is computed offline and another one using an online algorithm. A drawback with these approaches is their dependency on accurate network state information and precise loss models. To cope with these issues, we propose a new feedback solution that tracks the optimum using gradient estimation. Simulations in ns2 illustrate the behavior of the error correction schemes, demonstrating that the feedback solution outperforms the feedforward solution in presence of model errors. I.
Hybrid control of networked embedded systems
 European Journal of Control
, 2005
"... Hybrid systems that involve the interaction of continuous and discrete dynamics have been an active area of research for a number of years. In this paper, we start by briefly surveying the main theoretical control problems that have been treated in the hybrid systems setting and classify them into s ..."
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Cited by 5 (0 self)
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Hybrid systems that involve the interaction of continuous and discrete dynamics have been an active area of research for a number of years. In this paper, we start by briefly surveying the main theoretical control problems that have been treated in the hybrid systems setting and classify them into stabilization, optimal control and language specification problems. We then provide an overview of recent developments in four of the most prominent application areas of hybrid control methods: Control of power systems, industrial process control, design of automotive electronics and communication networks.
Y.: Integrated Computation, Communication and control: Towards Next Revolution
 in Information Technology. LNCS 3356, SpringerVerlag
, 2004
"... Abstract. There is a strong trend in modern industrial systems to integrate computation, communication, and control theories into networked control systems (NCSs). This is anticipated to be the next wave in the information technology revolution. From a control perspective, the interdisciplinary rela ..."
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Cited by 2 (2 self)
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Abstract. There is a strong trend in modern industrial systems to integrate computation, communication, and control theories into networked control systems (NCSs). This is anticipated to be the next wave in the information technology revolution. From a control perspective, the interdisciplinary relationship between computation, communication and control is illustrated through control loop timing analysis of NCSs. Critical issues in the emerging field of integrated computation, communication and control (ICCC) are discussed. Since it is difficult to analytically quantify the impacts of computation and communication constraints on the quality of control (QoC), a simulationbased approach is proposed. A numerical example of networked DC motor control is utilized in simulations, with different scheduling schemes and communication protocols employed. Results and analysis give valuable suggests for improving the control performance of NCSs which feature the integration of control with computation and communication. 1
P.R.: Architecture and mechanism design for realtime and faulttolerant Etherware for networked control
 In: Proceedings of the 17th IFAC World Congress
, 2008
"... Abstract: We believe that a standard control software framework which enables rapid, reliable and evolvable application development is the key for the proliferation of the networked control systems. Accordingly, we have been working on developing a domainware for general purpose control system, call ..."
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Cited by 2 (2 self)
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Abstract: We believe that a standard control software framework which enables rapid, reliable and evolvable application development is the key for the proliferation of the networked control systems. Accordingly, we have been working on developing a domainware for general purpose control system, called Etherware. Even though Etherware supports many of the distributed system domain requirements, it still needs further advances to be more suitable as a middleware for control systems. In this paper, we present an architecture and mechanisms for an enhanced middleware that supports networked control system design through enabling temporally correct interactions. We also propose an architecture and mechanisms for enhancing the robustness of networked control systems to faults, that we are currently implementing.
Codesign based Approach to Improve Robustness in Networked Control Systems
"... Traditional control systems consist of sensors, controllers, and actuators operating with tight periodic dependencies, and communicating over dedicated realtime channels such as CAN or FDDI. However, best effort networks such as 802.11 are being increasingly used in such systems. The unpredictable ..."
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Cited by 2 (2 self)
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Traditional control systems consist of sensors, controllers, and actuators operating with tight periodic dependencies, and communicating over dedicated realtime channels such as CAN or FDDI. However, best effort networks such as 802.11 are being increasingly used in such systems. The unpredictable delays and losses in such networks violate the periodicity assumptions of digital control design, and the consequent failsafe actions incur significant performance penalties. In this paper, we propose a codesign based approach to address the periodicity requirements of digital control design, and improve robustness by extending deadlines through graceful degradation to the failsafe action. In particular, we analytically demonstrate significant deadline extensions in the control loop of a traffic control testbed based on our approach. Such deadline extensions also facilitate fault tolerance techniques such as component restarts, and system management mechanisms such as online component upgrades. We validate the results by experiments in the testbed. 1.
Reducing Risk by Managing Software Related Failures in Networked Control Systems ⋆
"... Abstract — Managing risk is a central problem in the design and operation of networked control systems, and due to the increasing role and growing complexity of software in such systems, managing software related failures is becoming a central challenge. Even simple programming errors can cause cata ..."
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Cited by 2 (0 self)
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Abstract — Managing risk is a central problem in the design and operation of networked control systems, and due to the increasing role and growing complexity of software in such systems, managing software related failures is becoming a central challenge. Even simple programming errors can cause catastrophic failures [1]. Hence, it is vital to contain risks due to software related failures in such systems. Our main thesis is that most software related failures can be managed through relatively simple and generally applicable strategies, and such strategies can be effectively developed and reused with suitable support from software infrastructure such as middleware. We describe mechanisms in Etherware, our middleware for control over networks [2], for containing software failures, and demonstrate the effectiveness of these mechanisms through experiments in a vehicular control testbed. I.
Scheduling Automated Traffic on a Network of Roads
"... Abstract — We consider the problem of scheduling automated traffic in a city. Such automatic scheduling can improve efficiency of the system by decreasing delays, increasing capacity and easing congestion. The algorithms described in this paper can be thought of as belonging to a layer in the corres ..."
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Cited by 1 (0 self)
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Abstract — We consider the problem of scheduling automated traffic in a city. Such automatic scheduling can improve efficiency of the system by decreasing delays, increasing capacity and easing congestion. The algorithms described in this paper can be thought of as belonging to a layer in the corresponding controlcommunicationcomputational system which is responsible for generating timed trajectories for individual vehicles [1]. Each vehicle has a specified route from its origin to its destination, and the task of the scheduler is to provide timed trajectories for all vehicles, which follow the respective vehicles’ routes and further ensure that no collisions or deadlock will result. Our approach reduces the problem to a discretetime graph scheduling problem, by defining an appropriate graph to model the road network. Our main result is a sufficient condition on the graph of the road network and on the initial distribution of vehicles, under which there exists a scheduling algorithm that is guaranteed to clear the system in finite time. The nature of this result allows the design of provably correct scheduling algorithms that require only a small portion of future routes of all vehicles to be known, and are consequently able to work in real time. We also address the optimization of performance with respect to delay, by focusing on the “onestep move ” problem. Finding an optimal solution for the onestep problem would provide a greedy solution of the original networkwide scheduling problem, but is itself NPhard. We present a polynomial time heuristic algorithm and evaluate its performance through simulations.