Modeling formalisms for dynamic structure systems

We present a new concept for a system network to represent systems that are able to undergo structural change. Change in structure is defined in general terms, and includes the addition and deletion of systems and the modification of the relations among components. The structure of a system network is stored in the network executive. Any change in structure-related information is mapped into modifications in the network structure.Based on these concepts, we derive three new system specifications that provide a shorthand notation to specify classes of dynamic structure systems. These new formalisms are: dynamic structure discrete time system, dynamic structure differential equation specified systems, and dynamic structure discrete event system specification. We demonstrate that these formalisms are closed under coupling, making hierarchical model construction possible. formalisms are described using set theoretic notation and general systems theory concepts

Simulation of a Clustering Scheme for Vehicular Ad Hoc Networks Using a DEVS-based Virtual Laboratory Environment

ANT 2018, The 9th International Conference on Ambient Systems, Networks and Technologies, Porto, PORTUGAL, 08-/05/2018 - 11/05/2018Protocol design is usually based on the functional models developed according to the needs of the system. In Intelligent Transport Systems (ITS), the features studied regarding Vehicular Ad hoc Networks (VANET) include self-organizing, routing, reliability, quality of service, and security. Simulation studies on ITS-dedicated routing protocols usually focus on their performance in specific scenarios. However, the evolution of transportation systems towards autonomous vehicles requires robust protocols with proven or at least guaranteed properties. Though formal approaches provide powerful tools for system design, they cannot be used for every types of ITS components. Our goal is to develop new tools combining formal tools such as Event-B with DEVS-based (Discrete Event System Specification) virtual laboratories in order to design the models of ITS components which simulation would allow proving and verifying their properties in large-scale scenarios. This paper presents the models of the different components of a VANET realized with the Virtual Laboratory Environment (VLE). We point out the component models fitting to formal modeling, and proceed to the validation of all designed models through a simulation scenario based on real-world road traffic data

Foundations of Modelling and Simulation of Complex Systems

Modelling and simulation are becoming increasingly important enablers for the analysis and design of complex systems. In application domains such as automotive design, the notion of a "virtual experiment" is taken to the limit and complex designs are model-checked, simulated, and optimized extensively before a single realization is ever made. This "doing it right the first time" leads to tremendous cost savings and improved quality. Furthermore, with appropriate models, it is often possible to automatically synthesize (parts of) the system-to-be-built. In this paper, the basic concepts of modelling and simulation are introduced. These concepts are based on general systems theory and start from the idea of a model as an abstract representation of knowledge about structure and behaviour of some system. The purpose is either analysis or design in a particular experimental context. Typically, different formalisms are used such as Ordinary Differential Equations, Queueing Networks, and State Automata. It will be shown how these different formalisms all share a common structure and differ in the choice of time base, state space, and description of temporal evolution. This allows one to classify formalisms on the one hand and to find a common ground for implementing simulators on the other hand

Toward composing variable structure models and their interfaces: a case of intensional coupling definitions

In this thesis, we investigate a combination of traditional component-based and variable structure modeling. The focus is on a structural consistent specification of couplings in modular, hierarchical models with a variable structure. For this, we exploitintensional definitions, as known from logic, and introduce a novel intensional coupling definition, which allows a concise yet expressive specification of complex communication and interaction patterns in static as well as variable structure models, without the need to worryabout structural consistency.In der Arbeit untersuchen wir ein Zusammenbringen von klassischer komponenten-basierter und variabler Strukturmodellierung. Der Fokus liegt dabei auf der Spezifikation von strukturkonsistenten Kopplungen in modular-hierarchischen Modellen mit einer variablen Struktur. Dafür nutzen wir intensionale Definitionen, wie sie aus der Logik bekannt sind, und führen ein neuartiges Konzept von intensionalen Kopplungen ein, welches kompakte gleichzeitig ausdrucksstarke Spezifikationen von komplexen Kommunikations- und Interaktionsmuster in statischen und variablen Strukturmodellen erlaubt

Remote software upload techniques in future vehicles and their performance analysis

Updating software in vehicle Electronic Control Units (ECUs) will become a mandatory requirement for a variety of reasons, for examples, to update/fix functionality of an existing system, add new functionality, remove software bugs and to cope up with ITS infrastructure. Software modules of advanced vehicles can be updated using Remote Software Upload (RSU) technique. The RSU employs infrastructure-based wireless communication technique where the software supplier sends the software to the targeted vehicle via a roadside Base Station (BS). However, security is critically important in RSU to avoid any disasters due to malfunctions of the vehicle or to protect the proprietary algorithms from hackers, competitors or people with malicious intent. In this thesis, a mechanism of secure software upload in advanced vehicles is presented which employs mutual authentication of the software provider and the vehicle using a pre-shared authentication key before sending the software. The software packets are sent encrypted with a secret key along with the Message Digest (MD). In order to increase the security level, it is proposed the vehicle to receive more than one copy of the software along with the MD in each copy. The vehicle will install the new software only when it receives more than one identical copies of the software. In order to validate the proposition, analytical expressions of average number of packet transmissions for successful software update is determined. Different cases are investigated depending on the vehicle\u27s buffer size and verification methods. The analytical and simulation results show that it is sufficient to send two copies of the software to the vehicle to thwart any security attack while uploading the software. The above mentioned unicast method for RSU is suitable when software needs to be uploaded to a single vehicle. Since multicasting is the most efficient method of group communication, updating software in an ECU of a large number of vehicles could benefit from it. However, like the unicast RSU, the security requirements of multicast communication, i.e., authenticity, confidentiality and integrity of the software transmitted and access control of the group members is challenging. In this thesis, an infrastructure-based mobile multicasting for RSU in vehicle ECUs is proposed where an ECU receives the software from a remote software distribution center using the road side BSs as gateways. The Vehicular Software Distribution Network (VSDN) is divided into small regions administered by a Regional Group Manager (RGM). Two multicast Group Key Management (GKM) techniques are proposed based on the degree of trust on the BSs named Fully-trusted (FT) and Semi-trusted (ST) systems. Analytical models are developed to find the multicast session establishment latency and handover latency for these two protocols. The average latency to perform mutual authentication of the software vendor and a vehicle, and to send the multicast session key by the software provider during multicast session initialization, and the handoff latency during multicast session is calculated. Analytical and simulation results show that the link establishment latency per vehicle of our proposed schemes is in the range of few seconds and the ST system requires few ms higher time than the FT system. The handoff latency is also in the range of few seconds and in some cases ST system requires less handoff time than the FT system. Thus, it is possible to build an efficient GKM protocol without putting too much trust on the BSs

Models, Composability, and Validity

Composability is the capability to select and assemble simulation components in various combinations into simulation systems to satisfy specific user requirements. The defining characteristic of composability is the ability to combine and recombine components into different simulation systems for different purposes. The ability to compose simulation systems from repositories of reusable components has been a highly sought after goal among modeling and simulation developers. The expected benefits of robust, general composability include reduced simulation development cost and time, increased validity and reliability of simulation results, and increased involvement of simulation users in the process. Consequently, composability is an active research area, with both software engineering and theoretical approaches being developed. Composability exists in two forms, syntactic and semantic (also known as engineering and modeling). Syntactic composability is the implementation of components so that they can be connected. Semantic composability answers the question of whether the models implemented in the composition can be meaningfully composed

Approche modulaire pour la planification continue : application à la conduite des systèmes de culture

Dans le cadre de cette thèse, nous nous sommes intéressés à la conception des systèmes complexes autonomes opérant dans un environnement dynamique et incertain. Nous expliquons que la conduite des systèmes de culture d'une exploitation agricole est un problème multi-échelles spatiales et temporelles. La structure de l'exploitation étant fixée, elle intègre trois types de décision qui sont: l'allocation des cultures (à long terme), choix du mode de conduite des cultures, les itinéraires technique (à moyen terme) et l'ordonnancement des opérations agricoles journalières (à court terme). Ces problèmes de décision étant de nature différente, nous avons développé pour chacun d'eux des méthodes de planification spécifiques. Nous proposons d'aborder l'allocation des cultures comme un problème de satisfaction de contraintes pondérées où l'utilité de l'allocation est évaluée par une fonction de coût globale. Les modes de conduite des cultures étant prédéfinis, nous utilisons une approche de planification temporelle et hiérarchique dans laquelle l'heuristique de décomposition est une fonction globale permettant ainsi, de prendre en compte les interdépendances entre les effets de chaque mode de conduite. Enfin, l'approche que nous proposons pour l'ordonnancement des opérations agricoles est basée sur un modèle de programmation linéaire. Pour appréhender ces différents problèmes de décision, nous proposons une architecture systémique nommée "Safihr". Celle-ci est capable de prendre en compte l'entrelacement en ligne de plusieurs planificateurs spécifiques. Cette architecture repose sur le cadre des systèmes à événements discrets (DEVS). L'agent agriculteur est vu comme un système hiérarchique, dynamique et distribué en interaction avec son environnement physique. Chacun des planificateurs est vu comme un système de contrôle indépendant. "Safihr" intègre les mécanismes permettant de faire coopérer différents planificateurs au sein d'un même système.In this work, we address the challenge of the development of autonomous complex systems operating in a dynamic and uncertain environment. We only consider a farm with a cropping system and a determined structure. We explain that decision-making in farming systems is a complex issue in which decisions are joined up, through various spatial and scales. These decisions are usually grouped in three classes: strategic, tactical and operational decisions. Strategic decisions are long-term planning problems in which, knowing biophysical and structural constraints, crops are assigned to plots over a fixed horizon. Tactical decisions are mid-term planning problems in which, knowing crops to be grown, a crop management systems is assigned to each pair of plot and crop. Finally, operational decisions are short-term scheduling problems that could be summarized as scheduling daily farm operations to timely control crop production processes. Considering, the inherent feature of these decision-making problems, we developed for each of them a specific planning technique. Strategic decisions are address as a Weighted Constraint Satisfaction Problem in which the relevance of crops allocation is assessed by a global objective function. Tactical decisions are address as hierarchical and temporal planning problems, based on Hierarchical Tasks Networks and Simple Temporal Network. We introduced a new decomposition heuristic into HTN framework which enables to take into account the interdependence between crops production techniques. Finally, we proposed to tackle operational decisions by using linear programming techniques. To interleave these decision-making problems, we introduce a new modular architecture call Safihr "Simulation based Architecture For Interleaving Heterogeneous decisions in Real world problems". The proposed architecture is a model-based approach relying on Discrete EVent System specification formalism