1,720,979 research outputs found
Measurement Scheduling for Control Invariance in Networked Control Systems
No full textWe discuss a new reachability problem for networked controlled system where a master node - the controller - broadcasts commands to a set of slave nodes, which must take turn to relay back state measurements. This problem finds applications in some robotics and intelligent transportation systems setups. Constraints on communication demand a coupled design of the controller and the measurement schedule. We prove that the problem is formally equivalent to the Pinwheel Problem from scheduling theory, and building on this result we provide conditions for schedulability and reachability. The results are illustrated in three numerical examples
Receding-horizon robust online communication scheduling for constrained networked control systems
No full textThis paper proposes a novel online scheduling approach for perturbed Networked Control Systems (NCS) over lossy networks, subject to state and input constraints and limited network capacity. The paper shows how an online communication schedule can be found for the considered class of systems, as the solution of a constrained optimization problem, which is solved in receding horizon and is proven to be persistently feasible. The resulting online schedule is proven to preserve the system invariance w.r.t. state and input constraints. A communication scheduler is also derived for lossy networks, starting from a feasible baseline schedule calculated offline. Numerical examples are given to illustrate the proposed contributions
Scheduling and Robust Invariance in Networked Control Systems
Get PDFIn Networked Control Systems (NCS), impairments of the communication channel can be disruptive to stability and performance. In this paper, we consider the problem of scheduling the access to limited communication resources for a number of decoupled systems subject to state and input constraints, whose loops need to be closed over the network. The schedule must be designed to robustly preserve the invariance property of each system, which in turn guarantees constraint satisfaction. To that end, we first focus on systematic offline scheduling design to preserve robust invariance, and afterwards on online scheduling design with the aim of improving performance and compensating for packet losses while guaranteeing recursive schedulability
Optimal scheduling and control for constrained multi-agent networked control systems
Get PDFIn this paper, we study optimal control and communication schedule co-design for multi-agent networked control systems, with assuming shared parallel communication channels and uncertain constrained linear time-invariant discrete-time systems. To that end, we specify the communication demand for each system using an associated robust control invariant set and reachability analysis. We use these communication demands and invariant sets to formulate tube-based model predictive control and offline/online communication schedule co-design problems. Since the scheduling part includes an infinite dimension integer problem, we propose heuristics to find suboptimal solutions that guarantee robust constraints satisfaction and recursive feasibility. The effectiveness of our approach is illustrated through numerical simulations
Simultaneously Stabilizing Networked Systems with Minimal Communication
Get PDFSelf-triggered feedback control is used as a means to reduce the energy and communication requirements of networked systems. Triggered-control schemes result in aperiodic communications, with a potential for communication conflicts when multiple feedback loops are closed over a shared network. In this paper, we analyze the necessary/sufficient conditions for simultaneous stabilizability of a set of nonlinear systems over a network from the perspective of scheduling theory, using Lyapunov functions and input to state stability. We then propose a recursively feasible self-triggering scheme that minimizes the usage of the communication channel while ensuring the stability of all systems
Optimal Control Design for Perturbed Constrained Networked Control Systems
No full textThis letter focuses on an optimal control design problem for a class of perturbed networked control systems where a number of systems, subject to state and input constraints, share a communication network with limited bandwidth. We first formulate an optimal control design problem with a constant feedback gain in order to minimize the communication demand for each system while guaranteeing satisfaction of state and input constraints; we show that this optimization problem is very hard to solve. Then, we formulate the same optimal control design problem with a non-constant feedback gain; we argue that this problem is less difficult and results in a lower, or equal, communication demand in comparison to the design with the constant feedback gain. We illustrate and compare these optimal control designs by a simple example
Optimal scheduling and control for constrained multi-agent networked control systems
Get PDFIn this paper, we study optimal control and communication schedule co-design for multi-agent networked control systems, with assuming shared parallel communication channels and uncertain constrained linear time-invariant discrete-time systems. To that end, we specify the communication demand for each system using an associated robust control invariant set and reachability analysis. We use these communication demands and invariant sets to formulate tube-based model predictive control and offline/online communication schedule co-design problems. Since the scheduling part includes an infinite dimension integer problem, we propose heuristics to find suboptimal solutions that guarantee robust constraints satisfaction and recursive feasibility. The effectiveness of our approach is illustrated through numerical simulations
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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