Discrete-event Specification Research Articles

Mobile Communications-Enabled Smart Grid Cosimulator System Design

In this article, we present a system design approach for a simulator constructed in MATLAB/Simulink used to simulate power systems and the underlying communication system, i.e., device-to-device (D2D) communication protocol stack of long-term evolution (LTE). Emphasis is placed on the characterization of the continuous time-discrete event (CT-DE) cosimulation interface used to develop this simulator. We model the mapping of communication links between D2D nodes as a bipartite digraph, and proceed to characterize the dynamics of information exchange between power system signals and LTE nodes using the discrete event specification formalism. The joint CT-DE dynamics were tested with a simple fault location, isolation, and restoration application. The results indicated that the control signal shifts in the power system simulator were synchronized with the appropriate LTE messaging dynamics.

Devs based modeling and simulation of agricultural machinery movement

Field operations planning has become critical for the operational efficiency of agricultural activities, in terms of time and cost. To address this type of planning problem, we (1) developed a modeling capability built using a Discrete Event Simulation (DES) approach and object-oriented prgramming, and (2) propose a methodology extending field data to allow spatial operations on various geometric types. The simulation model developed using the Discrete Event Specification System (DEVS) formalism, captures the equipment characteristics and tracks the evolution of its movement across the field via state transition tables. The model is data driven and spatially and temporally detailed, which are key features to accurately estimate field efficiency. Our modeling approach offers more rigor in the component behavior definition and more flexibility enabling the handling of fields and equipment of various shapes and physical characteristics, respectively. The validity of the model was tested, with an error margin of 15%, by comparing its performance with empirical data collected from switchgrass harvesting equipment.

Distributed simulation platform to design advanced RFID based freight transportation systems

RFID systems, known to improve supply chains performances, are little implemented so far in industry, particularly in the field of transport, due to the high economic investment it requests in comparison to other existing solutions. However, their benefits may be theoretically proved by using a distributed simulation platform to support the design and test of any technical solution and organizational approach devoted to optimize RFID-based logistics systems. This paper deals with the development of this simulation platform, based on Generalized Discrete Event Specification (G-DEVS) models and HLA (High Level Architecture) standard. The different partner's components of the networked logistics enterprise are described. The proposed solution is applied to a freight transportation system and emulates the behaviour of the various components (RFID coupled to geolocation and mobile technology) required to optimize the products routing. The behaviour of the main components is G-DEVS formalized including the logistics supplier server, the smart product and the vehicle onboard device to interface the products with a centralized server. Delivery scenarios are then elaborated and simulated to check the behaviour and the intensity of communication network use between distributed G-DEVS models and other simulation components. The strength of the approach lies in the interoperability of the platform to simulate scenarios including discrete event models, real software and hardware devices all linked via an HLA connection. From these results, a discussion is given to validate or reject the conceptual choices about logistics components behaviour and their network bandwidth requirement regarding GSM, GPRS, Bluetooth and RFID networks theoretical capacities.

A parallel evolutionary algorithm to optimize dynamic memory managers in embedded systems

For the last 30 years, several dynamic memory managers ( DMMs) have been proposed. Such DMMs include first fit, best fit, segregated fit and buddy systems. Since the performance, memory usage and energy consumption of each DMM differs, software engineers often face difficult choices in selecting the most suitable approach for their applications. This issue has special impact in the field of portable consumer embedded systems, that must execute a limited amount of multimedia applications (e.g., 3D games, video players, signal processing software, etc.), demanding high performance and extensive memory usage at a low energy consumption. Recently, we have developed a novel methodology based on genetic programming to automatically design custom DMMs, optimizing performance, memory usage and energy consumption. However, although this process is automatic and faster than state-of-the-art optimizations, it demands intensive computation, resulting in a time-consuming process. Thus, parallel processing can be very useful to enable to explore more solutions spending the same time, as well as to implement new algorithms. In this paper we present a novel parallel evolutionary algorithm for DMMs optimization in embedded systems, based on the Discrete Event Specification ( DEVS) formalism over a Service Oriented Architecture ( SOA) framework. Parallelism significantly improves the performance of the sequential exploration algorithm. On the one hand, when the number of generations are the same in both approaches, our parallel optimization framework is able to reach a speed-up of 86.40× when compared with other state-of-the-art approaches. On the other, it improves the global quality (i.e., level of performance, low memory usage and low energy consumption) of the final DMM obtained in a 36.36% with respect to two well-known general-purpose DMMs and two state-of-the-art optimization methodologies.

DEVS/SOA: A Cross-Platform Framework for Net-centric Modeling and Simulation in DEVS Unified Process

Discrete Event Specification (DEVS) environments are implemented over middleware systems such as HLA, RMI, CORBA and others. DEVS exhibits concepts of systems theory and modeling and supports capturing the system behavior from the physical and behavioral perspectives. Further, they are implemented using object-oriented languages like Java and C++. This research work uses the Java platform to implement DEVS over a Service Oriented Architecture (SOA) framework. Called the DEVS/SOA, the framework supports a development and testing environment known as DEVS Unified Process that is built on a model continuity-based lifecycle methodology. DEVS Unified Process allows DEVS-based Modeling and Simulation (M&S) over net-centric platforms using DEVS/SOA. This framework also provides the crucial feature of run-time composability of coupled systems using SOA. We describe the architecture and designs of the server and the client. The client application communicates with multiple servers hosting DEVS simulation services. These simulation services are developed using the proposed symmetrical services architecture wherein the server can act as both a service provider and a service consumer contrary to the unidirectional client—server paradigm. We also discuss how this services-based architecture provides solutions for cross-platform distributed M&S. We demonstrate the DEVS/SOA framework with a scenario of Joint Close Air Support specified in Business Process Modeling Notation (BPMN). We also provide a real-world application of network health monitoring using DEVS/SOA-layered architectural framework.

EUDEVS: Executable UML with DEVS Theory of Modeling and Simulation

Modeling and simulation (M&S) for system design and prototyping is practiced today both in industry and academia. M&S are two different areas altogether and have specific objectives. However, most of the time these two separate areas are taken together. The developed code is woven tightly around both the model and the underlying simulator that executes it. This constrains both the model development and the simulation engine that has an impact on the scalability of the developed code. Furthermore, a lot of time is spent in developing a model because it needs both domain knowledge and simulation techniques, which also requires communication among users and developers. The Unified Modeling Language (UML) is widely accepted in industry, whereas discrete event specification (DEVS)-based modeling that separates the model and the simulator, provides a cleaner methodology to develop models and is much used in academia. DEVS today is used by engineers who understand discrete event modeling at a highly detailed level and are able to translate requirements to DEVS modeling code. There have been earlier efforts to integrate UML and DEVS but they have not succeeded in providing a transformation mechanism owing to inherent differences in these two modeling paradigms. In this paper we present an integrated approach to cross-transformations between UML and DEVS using the proposed eUDEVS, which stands for executable UML based on DEVS. Further, we also show that the obtained DEVS models belong to a specific class of DEVS models called finite deterministic DEVS (FD-DEVS) that is available as a W3C XML schema in XFD-DEVS. We also put the proposed eUDEVS in a much larger unifying framework called the DEVS unified process that allows bifurcated model-continuity-based lifecycle methodology for systems M&S. Finally, we demonstrate the concepts with a complete example.

A Formal Description Specification for Multi-Resolution Modeling Based on DEVS Formalism and its Applications

Multi-Resolution Modeling (MRM) is a relatively new research area. With the development of distributed interactive simulation, especially as the emergence of HLA (High Level Architecture), multi-resolution modeling becomes one of the key technologies for advanced modeling and simulation. But there is little research in the area of the theory of multi-resolution modeling, especially the formal description of MRM. In this paper, a new concept for the description of multi-resolution modeling, named Multi-resolution model Family (MF) is presented. A multi-resolution model family is defined as the set of different resolution models of the same entity. The description of MF includes two parts: models of different resolution and their relations. Based on this new concept and DEVS (Discrete Event Specification) formalism, a new multi-resolution model system specification, named MRMS (Multi-Resolution Model system Specification) is proposed. Some important properties of MRMS, especially the closure of MRMS under coupling operation are given and proved. MRMS provides a foundation and a powerful description tool for the research of MRM. An example to illustrate how to describe a multi-resolution model using our specification is given. Using this description, the theory and implementation of MRM can be further studied.

DECM, A User Oriented Formalism for High Level Discrete Event Specifications of Real-Time Systems

In this paper, we present DECM (Discrete Event Calculus Model), an original discrete event mathematical model for the specification of control systems at a high level of abstraction. Because the concept of event is more natural for nonspecialists than the concept of state, the proposed model is centered on the latter concept. This in turn permits the expression of asynchronous behavior without relying on the classical concept of state. In addition, DECM-based formalism offers an explicit representation of time that allows the use of timed simulations for the validation of formal specifications. This formalism is illustrated on a real-world industrial example.

An Embedded System's Design Verification Using Object-Oriented Simulation

The ability for the embedded system designer model and simulate proposed designs prior to implementation is increasingly valuable in today's competitive market place. Simulation- based design is a methodology that uses the vir tual prototype as a means of producing consis tent and reduced design time. This paper presents this approach in the context of an auto motive embedded system application. Struc tural models are used to capture design knowl edge and define the space of possible design alternatives. The Discrete Event Specification (DEVS) formalism is used to develop behavioral models which can be simulated. Results are ob tained through experimental frames which are used to define the scope of simulation. These re sults allow the designers to confirm that the proposed design solution meets the system re quirements and constraints.

Forest fire modelling and simulation in the DELTA environment

Traditional simulation methodology supports only changes in models state variables. Some models are better expressed by a combination of both changes in state variables and changes in structure. Dynamic Structure Discrete Event Specification (DSDEVS) is a recently introduced modelling and simulation formalism that provides full support for representing models with time varying structure. The DELTA simulation environment is an implementation of the DSDEVS formalism and provides full support to Structural Simulation. We show the advantages of the Dynamic Structure Cellular Automata describing the model of forest fire spreading and its implementation in the DELTA environment.

A Real-Time Discrete Event System Specification Formalismfor Seamless Real-Time Software Development

We present a time domain extension of the hierarchical and modular discrete event specification (DEVS) formalism. This extension is important for establishing a seamless real-time software development framework. Formalisms help describe a system unambiguously. If formal models are implemented without any consistent frameworks, however, it is hard to guarantee that there is no semantic gap between models and codes. Real-Time DEVS, named RTDEVS, is an extension of DEVS that can be characterized in three perspectives: the real time execution of models, the addition of time interval functions, and the activity specification for each state. After analyzing a system, the framework based on RTDEVS helps to expand each model of the system for executing in a real-time environment. In order to support the RTDEVS formalism, we propose abstract executive concepts based on the abstract simulator concepts of the DEVS formalism. Also, we implement an RTDEVS execution engine, named DEVS Executive, which runs on real-time Mach.