16,716 research outputs found
Modelling MAC-Layer Communications in Wireless Systems
We present a timed process calculus for modelling wireless networks in which
individual stations broadcast and receive messages; moreover the broadcasts are
subject to collisions. Based on a reduction semantics for the calculus we
define a contextual equivalence to compare the external behaviour of such
wireless networks. Further, we construct an extensional LTS (labelled
transition system) which models the activities of stations that can be directly
observed by the external environment. Standard bisimulations in this LTS
provide a sound proof method for proving systems contextually equivalence. We
illustrate the usefulness of the proof methodology by a series of examples.
Finally we show that this proof method is also complete, for a large class of
systems
Modelling and Refinement in CODA
This paper provides an overview of the CODA framework for modelling and
refinement of component-based embedded systems. CODA is an extension of Event-B
and UML-B and is supported by a plug-in for the Rodin toolset. CODA augments
Event-B with constructs for component-based modelling including components,
communications ports, port connectors, timed communications and timing
triggers. Component behaviour is specified through a combination of UML-B state
machines and Event-B. CODA communications and timing are given an Event-B
semantics through translation rules. Refinement is based on Event-B refinement
and allows layered construction of CODA models in a consistent way.Comment: In Proceedings Refine 2013, arXiv:1305.563
LTL Parameter Synthesis of Parametric Timed Automata
The parameter synthesis problem for parametric timed automata is undecidable
in general even for very simple reachability properties. In this paper we
introduce restrictions on parameter valuations under which the parameter
synthesis problem is decidable for LTL properties. The investigated bounded
integer parameter synthesis problem could be solved using an explicit
enumeration of all possible parameter valuations. We propose an alternative
symbolic zone-based method for this problem which results in a faster
computation. Our technique extends the ideas of the automata-based approach to
LTL model checking of timed automata. To justify the usefulness of our
approach, we provide experimental evaluation and compare our method with
explicit enumeration technique.Comment: 23 pages, extended versio
Behavioural equivalences for timed systems
Timed transition systems are behavioural models that include an explicit
treatment of time flow and are used to formalise the semantics of several
foundational process calculi and automata. Despite their relevance, a general
mathematical characterisation of timed transition systems and their behavioural
theory is still missing. We introduce the first uniform framework for timed
behavioural models that encompasses known behavioural equivalences such as
timed bisimulations, timed language equivalences as well as their weak and
time-abstract counterparts. All these notions of equivalences are naturally
organised by their discriminating power in a spectrum. We prove that this
result does not depend on the type of the systems under scrutiny: it holds for
any generalisation of timed transition system. We instantiate our framework to
timed transition systems and their quantitative extensions such as timed
probabilistic systems
Parametric Schedulability Analysis of Fixed Priority Real-Time Distributed Systems
Parametric analysis is a powerful tool for designing modern embedded systems,
because it permits to explore the space of design parameters, and to check the
robustness of the system with respect to variations of some uncontrollable
variable. In this paper, we address the problem of parametric schedulability
analysis of distributed real-time systems scheduled by fixed priority. In
particular, we propose two different approaches to parametric analysis: the
first one is a novel technique based on classical schedulability analysis,
whereas the second approach is based on model checking of Parametric Timed
Automata (PTA).
The proposed analytic method extends existing sensitivity analysis for single
processors to the case of a distributed system, supporting preemptive and
non-preemptive scheduling, jitters and unconstrained deadlines. Parametric
Timed Automata are used to model all possible behaviours of a distributed
system, and therefore it is a necessary and sufficient analysis. Both
techniques have been implemented in two software tools, and they have been
compared with classical holistic analysis on two meaningful test cases. The
results show that the analytic method provides results similar to classical
holistic analysis in a very efficient way, whereas the PTA approach is slower
but covers the entire space of solutions.Comment: Submitted to ECRTS 2013 (http://ecrts.eit.uni-kl.de/ecrts13
Timed Automaton Models for Simple Programmable Logic Controllers
We give timed automaton models for a class of Programmable Logic Controller (PLC) applications, that are programmed in a simple fragment of the language Instruction Lists as defined in the standard IEC 1131-3. Two different approaches for modelling timers are suggested, that lead to two different timed automaton models. The purpose of this work is to provide a basis for verification and testing of real-time properties of PLC applications. Our work can be seen in broader context: it is a contribution to methodical development of provably correct programs. Even if the present PLC hardware will be substituted by e.g. Personal Computers, with a similar operation mode, the development and verification method will remain useful
Properties of Distributed Time Arc Petri Nets
In recent work we started a research on a distributed-timed extension of Petri nets where time parameters are associated with tokens and arcs carry constraints that qualify the age of tokens required for enabling. This formalism enables to model e.g. hardware architectures like GALS. We give a formal definition of process semantics for our model and investigate several properties of local versus global timing: expressiveness, reachability and coverability
Probabilistic Timed Automata with Clock-Dependent Probabilities
Probabilistic timed automata are classical timed automata extended with
discrete probability distributions over edges. We introduce clock-dependent
probabilistic timed automata, a variant of probabilistic timed automata in
which transition probabilities can depend linearly on clock values.
Clock-dependent probabilistic timed automata allow the modelling of a
continuous relationship between time passage and the likelihood of system
events. We show that the problem of deciding whether the maximum probability of
reaching a certain location is above a threshold is undecidable for
clock-dependent probabilistic timed automata. On the other hand, we show that
the maximum and minimum probability of reaching a certain location in
clock-dependent probabilistic timed automata can be approximated using a
region-graph-based approach.Comment: Full version of a paper published at RP 201
Capturing Assumptions while Designing a Verification Model for Embedded Systems
A formal proof of a system correctness typically holds under a number of assumptions. Leaving them implicit raises the chance of using the system in a context that violates some assumptions, which in return may invalidate the correctness proof. The goal of this paper is to show how combining informal and formal techniques in the process of modelling and formal verification helps capturing these assumptions. As we focus on embedded systems, the assumptions are about the control software, the system on which the software is running and the systemās environment. We present them as a list written in natural language that supplements the formally verified embedded system model. These two together are a better argument for system correctness than each of these given separately
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