| 1. |
- Altaf, Faisal, et al.
(author)
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Wireless event-triggered controller for a 3D tower crane lab process
- 2011
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In: 2011 19th Mediterranean Conference on Control and Automation, MED 2011. - 9781457701252 - 9781457701245 ; , s. 994-1001
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Conference paper (peer-reviewed)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.
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| 2. |
- Molin, Adam, et al.
(author)
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Innovations-based priority assignment for control over CAN-like networks
- 2015
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In: 54th IEEE Conference on Decision and Control (CDC). - : IEEE conference proceedings. ; , s. 4163-4169
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Conference paper (peer-reviewed)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.
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| 3. |
- Sou, Kin Cheong, et al.
(author)
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On the Exact Solution to a Smart Grid Cyber-Security Analysis Problem
- 2013
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In: IEEE Transactions on Smart Grid. - : IEEE Press. - 1949-3053 .- 1949-3061. ; 4:2, s. 856-865
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Journal article (peer-reviewed)abstract
- This paper considers a smart grid cyber-security problem analyzing the vulnerabilities of electric power networks to false data attacks. The analysis problem is related to a constrained cardinality minimization problem. The main result shows that an l1 relaxation technique provides an exact optimal solution to this cardinality minimization problem. The proposed result is based on a polyhedral combinatorics argument. It is different from well-known results based on mutual coherence and restricted isometry property. The results are illustrated on benchmarks including the IEEE 118-bus, IEEE 300-bus and the Polish 2383-bus and 2736-bus systems.
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| 4. |
- Di Marco, Piergiuseppe, et al.
(author)
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Effects of Rayleigh-lognormal fading on IEEE 802.15.4 networks
- 2013
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In: Communications (ICC), 2013 IEEE International Conference on. - : IEEE conference proceedings. - 9781467331227 ; , s. 1666-1671
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Conference paper (peer-reviewed)abstract
- The IEEE 802.15.4 communication protocol is a de-facto standard for wireless applications in industrial and home automation. Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been thoroughly investigated under the assumption of ideal wireless channel, there is still a lack of understanding of the cross-layer interactions between MAC and physical layer in the presence of realistic wireless channel models that include path loss, multi-path fading and shadowing. In this paper, an analytical model of these dynamics is proposed. The analysis considers simultaneously a composite Rayleigh-lognormal channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. It is shown that the reliability of the contention-based MAC over fading channels is often far from that derived under ideal channel assumptions. Moreover, it is established to what extent fading may be beneficial for the overall network performance.
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| 5. |
- Farokhi, Farhad, 1987-
(author)
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Decentralized Control of Networked Systems : Information Asymmetries and Limitations
- 2014
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Doctoral thesis (other academic/artistic)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.
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| 6. |
- Farokhi, Farhad, 1987-, et al.
(author)
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Networked Estimation Using Sparsifying Basis Prediction
- 2013
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In: IFAC Proceedings Volumes. - 9783902823557 ; , s. 174-181
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Conference paper (peer-reviewed)abstract
- We present a framework for networked state estimation, where systems encode their (possibly high dimensional) state vectors using a mutually agreed basis between the system and the estimator (in a remote monitoring unit). The basis sparsifies the state vectors, i.e., it represents them using vectors with few non-zero components, and as a result, the systems might need to transmit only a fraction of the original information to be able to recover the non-zero components of the transformed state vector. Hence, the estimator can recover the state vector of the system from an under-determined linear set of equations. We use a greedy search algorithm to calculate the sparsifying basis. Then, we present an upper bound for the estimation error. Finally, we demonstrate the results on a numerical example.
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| 7. |
- Jacobsson, Krister, et al.
(author)
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ACK-clocking dynamics: Modelling the interaction between windows and the network
- 2008
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In: 27TH IEEE CONFERENCE ON COMPUTER COMMUNICATIONS (INFOCOM). - 9781424420254 ; , s. 181-185
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Conference paper (peer-reviewed)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.
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| 8. |
- Meng, Z., et al.
(author)
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Multiagent systems with compasses
- 2015
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In: SIAM Journal of Control and Optimization. - : Society for Industrial & Applied Mathematics (SIAM). - 0363-0129 .- 1095-7138. ; 53:5, s. 3057-3080
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Journal article (peer-reviewed)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.
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| 9. |
- Ramesh, Chithrupa, et al.
(author)
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State-based Priorities for Tournaments in Wireless Networked Control Systems
- 2014
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Other publication (other academic/artistic)abstract
- We introduce a state-based distributed prioritization mechanism for a sensor associated with a dynamical system to access a wireless network, when multiple such systems share the same network link. The priorities, designated Attention Factors, are assigned by each sensor to its data packets, based on measurements of the system state. The Attention Factor represents a quantized value of the minimum risk in not transmitting a given measurement. The Attention Factors from different sensors are evaluated and allotted slots, in a distributed manner, using a dominance-based protocol called tournaments. Packets with the same Attention Factor in a tournament collide, and are lost. We analytically evaluate the probability of a successful transmission using this access mechanism. We also find an upper bound for the estimation and control performance of a system using tournament access, which shows the benefits of using state-based priorities. The proposed tournament mechanism is implemented on the IEEE 802.15.4 standard protocol stack, and evaluated in a hardware-in-the-loop experimental setup.
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| 10. |
- van Dooren, Dirk, et al.
(author)
-
Safety Analysis for Controller Handover in Mobile Systems
- 2017
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In: IFAC-PapersOnLine. - : Elsevier. - 2405-8963.
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Conference paper (peer-reviewed)abstract
- Next generation mobile networks are envisioned to provide support for real-time control applications. One of the main aspects of these systems is that the location of the controller may be separated from the location of sensing and actuation. This promises benefits in terms of an increased flexibility, lower costs due to resource sharing, and higher computational capabilities. This paper focuses on one aspect of such systems, specifically, the controller handover. During a controller handover, a control process is moved from one point of computation to another at runtime. A possible reason for performing such a handover is to move the control process to a controller with better channel conditions. The safety of the handover is analyzed using a probabilistic reachability analysis by modeling the handover procedure as a stochastic hybrid system. Based on this safety analysis, a safety-oriented handover triggering rule is proposed. This triggering rule is shown to be dependent on the instantaneous state of the plant, in contrast to handover in mobile networks where it is only dependent on the state of the communication links. A vehicle platoon is considered as an example scenario, which is controlled by a base station of a mobile network. While driving, the platoon will move out of the communication range of the base station, so the control process needs to be moved to the next base station. Simulations illustrate the conditions for a safe execution of so called hard and soft handover protocols.
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