1,721,092 research outputs found
QoS Control for Pipelines of Tasks using Multiple Resources
No full textWe consider soft real-time applications organized as pipelines of tasks using resources of different type (communication, computation, and storage). The applications are assumed to be periodically triggered and the different tasks communicate by unidirectional buffers. The problem we cope with is how to effectively share the resources so that some specified Quality of Service (QoS) requirements are met. The QoS considered here is tightly related to the end-to-end temporal behavior of the application. To compensate for time-varying resource requirements, we advocate a distributed control approach whereby the scheduling parameters of each task are tuned depending on the temporal behavior of the application measured by appropriate sensors. The use of real-time scheduling strategies enables a mathematically safe control design in which the QoS requirements are translated into control goals, and formal proofs are provided on the ability of the controller to fulfil these goals. We also offer extensive simulations that validate the approach for multimedia applications
Trading Security for Control Performance in Distributed Robotic Applications
No full textNetworked embedded and control systems are largely used in factory automation for production and logistics tasks. In this application domain, security has become a prominent issue due to the critical consequences a cyber attack may have in terms of safety and financial losses. Unfortunately security solutions compete against control applications for the often scarce resources of embedded platforms. In this paper, we show how security can be dealt with as one of different Quality of Service dimensions and traded for control performance in an adaptive QoS management scheme. The system is able to respond to increased resource requirements or to changes in the risk level by reconfiguring the application modes and the security modes. We offer an explanatory case study to show how this idea is implemented
On the complexity of core, kernel, and bargaining set
No full textCoalitional games model scenarios where players can collaborate by forming coalitions in order to obtain higher worths than by acting in isolation. A fundamental issue of coalitional games is to single out the most desirable outcomes in terms of worth distributions, usually called solution concepts. Since decisions taken by realistic players cannot involve unbounded resources, recent computer science literature advocated the importance of assessing the complexity of computing with solution concepts. In this context, the paper provides a complete picture of the complexity issues arising with three prominent solution concepts for coalitional games with transferable utility, namely, the core, the kernel, and the bargaining set, whenever the game worth-function is represented in some reasonably compact form. The starting points of the investigation are the settings of graph games and of marginal contribution nets, where the worth of any coalition can be computed in polynomial time in the size of the game encoding and for which various open questions were stated in the literature. The paper answers these questions and, in addition, provides new insights on succinctly specified games, by characterizing the computational complexity of the core, the kernel, and the bargaining set in relevant generalizations and specializations of the two settings. Concerning the generalizations, the paper shows that dealing with arbitrary polynomial-time computable worth functions—no matter of the specific game encoding being considered—does not provide any additional source of complexity compared to graph games and marginal contribution nets. Instead, only for the core, a slight increase in complexity is exhibited for classes of games whose worth functions encode NP-hard optimization problems, as in the case of certain combinatorial games. As for specializations, the paper illustrates various tractability results on classes of bounded treewidth graph games and marginal contribution networks
Non-Transferable Utility Coalitional Games via Mixed-Integer Linear Constraints
No full textCoalitional games serve the purpose of modeling payoff distribution problems in scenarios where agents can collaborate by forming coalitions in order to obtain higher worths than by acting in isolation. In the classical Transferable Utility (TU) setting, coalition worths can be freely distributed amongst agents. However, in several application scenarios, this is not the case and the Non-Transferable Utility setting (NTU) must be considered, where additional application-oriented constraints are imposed on the possible worth distributions.
In this paper, an approach to define NTU games is proposed which is based on describing allowed distributions via a set of mixed-integer linear constraints applied to an underlying TU game. It is shown that such games allow non-transferable conditions on worth distributions to be specified in a natural and succinct way. The properties and the relationships among the most prominent solution concepts for NTU games that hold when they are applied on (mixed-integer) constrained games are investigated. Finally, a thorough analysis is carried out to assess the impact of issuing constraints on the computational complexity of some of these solution concepts
Adaptive Real-Time Scheduling for Legacy Multimedia Applications
No full textMultimedia applications are often executed on standard Personal Computers. The absence of established standards has hindered the adoption of real-time scheduling solutions in this class of applications. Developers have adopted a wide range of heuristic approaches to achieve an acceptable timing behaviour but the result is often unreliable. We propose a mechanism to extend the benefits of real-time scheduling to legacy applications based on the combination of two techniques: 1) a real-time monitor that observes and infers the activation period of the application, and 2) a feedback mechanism that adapts the scheduling parameters to improve its real-time performance
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