| 1. |
- Farokhi, Farhad, 1987-
(författare)
-
Decentralized Control of Networked Systems : Information Asymmetries and Limitations
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Designing local controllers for networked systems is challenging, because in these systems each local controller can often access only part of the overall information on system parameters and sensor measurements. Traditional control design cannot be easily applied due to the unconventional information patterns, communication network imperfections, and design procedure complexities. How to control large-scale systems is of immediate societal importance as they appear in many emerging applications, such as intelligent transportation systems, smart grids, and energy-efficient buildings. In this thesis, we make three contributions to the problem of designing networked controller under information asymmetries and limitations.In the first contribution, we investigate how to design local controllers to optimize a cost function using only partial knowledge of the model governing the system. Specifically, we derive some fundamental limitations in the closed-loop performance when the design of each controller only relies on local plant model information. Results are characterized in the structure of the networked system as well as in the available model information. Both deterministic and stochastic formulations are considered for the closed-loop performance and the available information. In the second contribution of the thesis, we study decision making in transportation systems using heterogeneous routing and congestion games. It is shown that a desirable global behavior can emerge from simple local strategies used by the drivers to choose departure times and routes. Finally, the third contribution is a novel stochastic sensor scheduling policy for ad-hoc networked systems, where a varying number of control loops are active at any given time. It is shown that the policy provides stochastic guarantees for the network resources dynamically allocated to each loop.
|
|
| 2. |
- Meng, Z., et al.
(författare)
-
Multiagent systems with compasses
- 2015
-
Ingår i: SIAM Journal of Control and Optimization. - : Society for Industrial & Applied Mathematics (SIAM). - 0363-0129 .- 1095-7138. ; 53:5, s. 3057-3080
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates agreement protocols over cooperative and cooperativeantagonistic multiagent networks with coupled continuous-time nonlinear dynamics. To guarantee convergence for such systems, it is common in the literature to assume that the vector field of each agent is pointing inside the convex hull formed by the states of the agent and its neighbors, given that the relative states between each agent and its neighbors are available. This convexity condition is relaxed in this paper, as we show that it is enough that the vector field belongs to a strict tangent cone based on a local supporting hyperrectangle. The new condition has the natural physical interpretation of requiring shared reference directions in addition to the available local relative states. Such shared reference directions can be further interpreted as if each agent holds a magnetic compass indicating the orientations of a global frame. It is proved that the cooperative multiagent system achieves exponential state agreement if and only if the time-varying interaction graph is uniformly jointly quasi-strongly connected. Cooperative-antagonistic multiagent systems are also considered. For these systems, the relation has a negative sign for arcs corresponding to antagonistic interactions. State agreement may not be achieved, but instead it is shown that all the agents' states asymptotically converge, and their limits agree componentwise in absolute values if and in general only if the time-varying interaction graph is uniformly jointly strongly connected.
|
|
| 3. |
- Terelius, Håkan, et al.
(författare)
-
Converging an Overlay Network to a Gradient Topology
- 2011
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the topology convergence problem for the gossip-based Gradient overlay network. In an overlay network where each node has a local utility value, a Gradient overlay network is characterized by the properties that each node has a set of neighbors containing higher utility values, such that paths of increasing utilities emerge in the network topology. The Gradient overlay network is built using gossiping and a preference function that samples from nodes using a uniform random peer sampling service. We analyze it using tools from matrix analysis, and we prove both the necessary and sufficient conditions for convergence to a complete gradient structure, as well as estimating the convergence time. Finally, we show in simulations the potential of the Gradient overlay, by building a more efficient live-streaming peer-to-peer (P2P) system than one built using uniform random peer sampling.
|
|
| 4. |
- Jacobsson, Krister, et al.
(författare)
-
ACK-clocking dynamics: Modelling the interaction between windows and the network
- 2008
-
Ingår i: 27TH IEEE CONFERENCE ON COMPUTER COMMUNICATIONS (INFOCOM). - 9781424420254 ; , s. 181-185
-
Konferensbidrag (refereegranskat)abstract
- A novel continuous time fluid flow model of the dynamics of the interaction between ACK-clocking and the link buffer is presented.. A fundamental integral equation relating the instantaneous flow rate and the window dynamics is derived. Properties of the model, such as well-posedness and stability, are investigated. Packet level experiments verily that this new model is more accurate than existing models, correctly predicting qualitatively different behaviors, for example when round trill delays are heterogeneous.
|
|
| 5. |
- Ahlén, Anders, et al.
(författare)
-
Towards Wireless Control in Industrial Process Automation : A Case Study at a Paper Mill
- 2019
-
Ingår i: IEEE CONTROL SYSTEMS MAGAZINE. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1066-033X .- 1941-000X. ; 39:5, s. 36-57
-
Tidskriftsartikel (refereegranskat)abstract
- Wireless sensors and networks are used only occasionally in current control loops in the process industry. With rapid developments in embedded and highperformance computing, wireless communication, and cloud technology, drastic changes in the architecture and operation of industrial automation systems seem more likely than ever. These changes are driven by ever-growing demands on production quality and flexibility. However, as discussed in "Summary," there are several research obstacles to overcome. The radio communication environment in the process industry is often troublesome, as the environment is frequently cluttered with large metal objects, moving machines and vehicles, and processes emitting radio disturbances [1], [2]. The successful deployment of a wireless control system in such an environment requires careful design of communication links and network protocols as well as robust and reconfigurable control algorithms.
|
|
| 6. |
- Sandberg, Henrik, et al.
(författare)
-
Cyberphysical security in networked control systems : An introduction to the issue
- 2015
-
Ingår i: IEEE CONTR SYST MAG. - 1066-033X. ; 35:1, s. 20-23
-
Tidskriftsartikel (refereegranskat)abstract
- This special issue provides an introduction to cyberphysical security of networked control systems (NCSs) and summarizes recent progress in applying fundamentals of systems theory and decision sciences to this new and increasingly promising area. NCS applications range from large-scale industrial applications to critical infrastructures such as water, transportation, and electricity networks. The security of NCSs naturally depends on the integration of cyber and physical dynamics and on different ways in which they are affected by the actions of human decision makers. Thus, problems in this area lie at the intersection of control systems and computer security. The six articles that constitute this special issue approach cyberphysical security from a variety of perspectives, including control theory, optimization, and game theory. They cover a range of topics such as models of attack and defense, risk assessment, his special issue provides an introduction to cyberphysical security of networked control systems (NCSs) and summarizes recent progress in applying fundamentals of systems theory and decision sciences to this new and increasingly promising area. NCS applications range from large-scale industrial applications to critical infrastructures such as water, transportation, and electricity networks. The security of NCSs naturally depends on the integration of cyber and physical dynamics and on different ways in which they are affected by the actions of human decision makers. Thus, problems in this area lie at the intersection of control systems and computer security. The six articles that constitute this special issue approach cyberphysical security from a variety of perspectives, including control theory, optimization, and game theory. They cover a range of topics such as models of attack and defense, risk assessment,attack detection and identification, and secure control design.A common theme among these contributions is an emphasis on the development of a principled approach to cyberphysical security of NCS.
|
|
| 7. |
- Shames, Iman, et al.
(författare)
-
Agents Misbehaving in a Network : a Vice or a Virtue?
- 2012
-
Ingår i: IEEE Network. - : IEEE Communications Society. - 0890-8044 .- 1558-156X. ; 26:3, s. 35-40
-
Tidskriftsartikel (refereegranskat)abstract
- Misbehaviors among the agents in a network might be intentional or unintentional, they might cause a system-wide failure or they might improve the performance or even enable us to achieve an objective. In this article we consider examples of these possible scenarios. First, we argue the necessity of monitoring the agents in a network to detect if they are misbehaving or not and outline a distributed method in which each agent monitors its neighbors for any sign of misbehavior. Later, we focus on solving the problem of distributed leader selection via forcing the agents to temporarily misbehave, and introduce an algorithm that enables the agents in a network to select their leader without any interference from the outside of the network.
|
|
| 8. |
- Altaf, Faisal, et al.
(författare)
-
Wireless event-triggered controller for a 3D tower crane lab process
- 2011
-
Ingår i: 2011 19th Mediterranean Conference on Control and Automation, MED 2011. - 9781457701252 - 9781457701245 ; , s. 994-1001
-
Konferensbidrag (refereegranskat)abstract
- This paper studies the design and real-time implementation of an event-triggered controller for a nonlinear 3D tower crane where the communication between the controller and the actuators is performed over a low-power wireless network. A flexible Event-Generation Circuit (EGC) is proposed in order to implement event-driven controllers for Networked Control Systems. Furthermore, a detailed experimental analysis on the performance of the event-triggered controller and the influence of packet losses on the transmitted actuation messages are presented. The results show that the event-triggered controllers in networked control systems are able to maintain the same level of performance as compared to periodic controllers, while increasing the sensors/actuators lifetime by reducing network bandwidth utilization.
|
|
| 9. |
- Shi, Guodong, et al.
(författare)
-
Consensus Over Random Graph Processes : Network Borel-Cantelli Lemmas for Almost Sure Convergence
- 2015
-
Ingår i: IEEE Transactions on Information Theory. - : IEEE Communications Society. - 0018-9448 .- 1557-9654. ; 61:10, s. 5690-5707
-
Tidskriftsartikel (refereegranskat)abstract
- Distributed consensus computation over random graph processes is considered. The random graph process is defined as a sequence of random variables which take values from the set of all possible digraphs over the node set. At each time step, every node updates its state based on a Bernoulli trial, independent in time and among different nodes: either averaging among the neighbor set generated by the random graph, or sticking with its current state. The connectivity-independence and arc-independence are introduced to capture the fundamental influence of the random graphs on the consensus convergence. Necessary and/or sufficient conditions are presented on the success probabilities of the Bernoulli trials for the network to reach a global almost sure consensus, with some sharp threshold established revealing a consensus zero-one law. Convergence rates are established by the lower and upper bounds of the epsilon-computation time. We also generalize the concepts of connectivity/arc independence to their analogues from the *-mixing point of view, so that our results apply to a very wide class of graphical models, including the majority of random graph models in the literature, e.g., Erdos-Renyi, gossiping, and Markovian random graphs. We show that under *-mixing, our convergence analysis continues to hold and the corresponding almost sure consensus conditions are established. Finally, we further investigate almost sure finite-time convergence of random gossiping algorithms, and prove that the Bernoulli trials play a key role in ensuring finite-time convergence. These results add to the understanding of the interplay between random graphs, random computations, and convergence probability for distributed information processing.
|
|
| 10. |
- Molin, Adam, et al.
(författare)
-
Innovations-based priority assignment for control over CAN-like networks
- 2015
-
Ingår i: 54th IEEE Conference on Decision and Control (CDC). - : IEEE conference proceedings. ; , s. 4163-4169
-
Konferensbidrag (refereegranskat)abstract
- We present an innovations-based prioritization mechanism to efficiently use network resources for data gathering, without compromising the real-time decision making capability of the control systems. In the envisioned protocol, each sensor assigns the Value of Information (VoI) contained in its current observations for the network as the priority. Tournaments are used to compare priorities and assign transmission slots, like in the CAN bus protocol. By using a rollout strategy, we derive feasible algorithms for computing the VoI-based priorities for the case of coupled and decoupled systems. In the case of decoupled systems, performance guarantees with regard to the control cost of the VoI-based strategy are identified. We illustrate the efficiency of the proposed approach on a platooning example in which the vehicles receive measurements from multiple sensors.
|
|
