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29
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 49 (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 21 (4 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 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 10 (3 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.
Dependency algebra: A tool for designing robust realtime systems
 RTSS 2005
, 2005
"... A robust system is one that can ensure essential services in spite of faults and failures in useful but nonessential components. Unless we can ensure that critical services can only USE but not depend on less critical components, a seemingly minor fault can propagate along complex and implicit depe ..."
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Cited by 9 (4 self)
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A robust system is one that can ensure essential services in spite of faults and failures in useful but nonessential components. Unless we can ensure that critical services can only USE but not depend on less critical components, a seemingly minor fault can propagate along complex and implicit dependency chains and bring down the system. Modern real time systems are often developed concurrently by multiple teams. A team typically only knows the dependency relations between their components and neighboring components. In addition, dependency relations will change as software components and their interactions are being modified. Therefore, how to automatically track and analyze the system wide dependency from local information is important for the development of robust real time systems. This paper presents dependency algebra a unified theoretical framework plus a prototype toolkit for dependency management in realtime systems.
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
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.
On Stability in Presence of Analog Erasure Channels
 Mathematical Theory of Networks and Systems
, 2008
"... Abstract — Consider a discretetime networked control scheme, in which the controller has direct access to noisy measurements of the plant’s output, but the controller and the actuator are connected via a link that features Bernoulli erasure events. We determine necessary and sufficient conditions ..."
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Cited by 4 (1 self)
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Abstract — Consider a discretetime networked control scheme, in which the controller has direct access to noisy measurements of the plant’s output, but the controller and the actuator are connected via a link that features Bernoulli erasure events. We determine necessary and sufficient conditions for the stabilizability of an unstable linear and timeinvariant plant. We show that these conditions are identical for two types of actuators: • (Type I) Processing at the actuator has access to the plant’s model; • (Type II) Processing at the actuator uses a universal algorithm that does not depend on the model of the plant. We also identify cases where availability of acknowledgements over the controlleractuator channel is not required for stability. We also consider decentralized networked control structures, where two or more independent controllerlinkactuator assemblies have access to different measurements of the plant’s output. I.
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 3 (3 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.
Static Analysis to Enforce Safe Value Flow in Embedded Control Systems
"... Embedded control systems consist of multiple components with different criticality levels interacting with each other. For example, in a passenger jet, the navigation system interacts with the passenger entertainment system in providing passengers the distancetodestination information. It is imper ..."
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Cited by 2 (0 self)
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Embedded control systems consist of multiple components with different criticality levels interacting with each other. For example, in a passenger jet, the navigation system interacts with the passenger entertainment system in providing passengers the distancetodestination information. It is imperative that failures in the noncritical subsystem should not compromise critical functionality. This architectural principle for robustness can, however, be easily compromised by implementationlevel errors. We describe SafeFlow, which statically analyzes core components in the system to ensure that they use noncore values communicated through shared memory only if they are runtime monitored for safety or recoverability. Using simple, local annotations and semantic restrictions on shared memory usage in the core component, SafeFlow precisely identifies accesses to unmonitored noncore values. With a few false positives, it identifies erroneous dependencies of critical data on noncore values that can arise due to programming errors, inadvertent accesses, or wrong assumptions regarding the absence of difficulttodetect implementation errors such as data races and synchronization. We demonstrate the utility of SafeFlow by applying it to discover critical value flow dependencies in three prototype systems.
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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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.