Mohammad Moallemi

Designing an interface for real-time and embedded DEVS

In this work, we are proposing a hardware-in-the-loop model-driven method to develop real-time and embedded applications based on DEVS (Discrete Event Systems Specification) formalism. This approach combines the advantages of a simulation-based approach with the rigor of a formal methodology. This framework can be used to develop embedded applications incrementally, and integrate simulation models with hardware components seamlessly. We have defined structural modifications to the current DEVS abstract simulator, allowing for integration with hardware devices, using external ports of the model and adding hardware control mechanisms. The use of this methodology provides model continuity from the early stages of model design to embedding it on the target. We have discussed the details of implementation of the proposed technique on E-CD++ (a DEVS based toolkit).

Modeling and simulation-driven development of embedded real-time systems

Abstract The design and development of embedded hard real-time (RT) systems is one of the complex development practices, because of the requirements of criticality and timeliness of these systems. One critical aspect of RT systems is the production of output before specified deadline. Formal methods are promising in dealing with the design issues of these applications, although they do not scale well for complex systems. Instead, Modeling and Simulation (M&S) provides a cost-effective approach to verify the design and implementation details of very Complex RT applications. M&S methods provide dynamic and risk-free testing environments to verify different scenarios, and they are used for feasibility analysis and verification of such systems. Nevertheless, the simulation models are usually discarded in the later phases of the development. We present the application of an M&S-based method referred to as DEVSRT (Discrete EVent System Specifications in Real-Time) to solve the discontinuity between the simulation models and the final embedded application, in this paper. DEVSRT defines explicit deadline notation for DEVS transitions, draws a clear mapping between DEVS transitions and real-time tasks and provides a formal method and tool for integration of simulation models with the associated hardware components.

Modeling and simulation of crowd using cellular discrete event systems theory

In this paper, we discuss how Cellular Discrete Event System Specification (Cell-DEVS) theory can be used in modeling and simulation of the crowd. We will show that the efficient cell update mechanism of Cell-DEVS allows for more efficient entity-based simulation of the crowd compared to cellular automata. On the other hand the formal interfacing mechanisms provided by this theory allows for integration of other components such as DEVS atomic processing component or visualization and building information modeling components with the Cell-DEVS model. Finally, we describe in details of the design and development of several pedestrian models and present the results.

Data Upload in LTE-A Mobile Networks by Using Shared Segmented Upload

There have been ongoing efforts focused on improving mobile networks standards to support the ever-increasing user demands of high data rate services. These efforts are more crucial for cell-edge users where their long distance from their serving Base Station (BS), and the higher interference from the neighbouring cells, degrades their performance. Contemporary communication standards, proposed for Fourth Generation (4G) of mobile telecommunication standards, use different techniques to deal with these bottlenecks. Long Term Evolution Advanced (LTE-A), is a promising standard for 4G mobile networks, and it uses different technologies to enhance users’ performance regardless of their location in the coverage area. LTE-A employs Coordinated Multi-Point (CoMP) technique particularly to provide high data rate services for cell-edge users. In this context, we present Shared Segmented Upload (SSU), a novel method for uploading large files from User Equipment (UE) to multiple BSs in a CoMP communication scenario. We use Discrete EVent System Specification (DEVS) formalism to model an LTE-A mobile network using SSU. In addition, we employ DEVS to simulate a conventional non-cooperative algorithm to evaluate the effectiveness of SSU in two scenarios: rural and urban area settings. The simulation results show that, compared to the conventional method, SSU improves cell-edge users’ uplink performance and reduces the latency for a UE to upload its data to the network.

DEVS Graph In Modelica For Real-Time Simulation.

Two new Modelica libraries are presented. The first library, named GGADLib, supports the DEVS graph notation in Modelica. The second Modelica library, named UDPLib, allows sending and receiving data using the User Datagram Protocol (UDP). GGADLib uses UDPLib. As a result, DEVS graph models composed using GGADLib can receive and send data (input and output events, according to DEVS terminology) using UDP. This feature allows Modelica DEVS graph models to communicate with hardware and with other models, e.g., with models developed using other languages and tools, and running in other computers. The implementation of UDPLib and GGADLib is discussed in this paper. Their use is illustrated by means of a case study: evaluating an obstacle avoidance controller for the e-puck mobile robot. The UDPLib and GGADLib Modelica libraries can be freely downloaded from http://www.euclides.dia.uned.es/

Application of RT-DEVS in military

Today, model based simulation is a popular scheme for simulating real world events. There has been some effort to use the same models that have been developed for simulation purposes for control applications. This approach permits model reuse and reliability for critical embedded control applications. In this paper a simulation model of an autonomous robot has been used to control a simulated reconnaissance vehicle on battle field. Since it is very costly to construct a real battle field situation and to verify the performance of military devices, model continuity from simulation to embedded control is a cost-effective and easy process for developing military applications. We have used DEVS (Discrete EVent System specification) formalism to define the robotic vehicle model and conducted variety of tests by simulation variety of scenarios. The final model has been embedded on a tank shaped robot.

Simulation of three dimensional elevator system using cell-DEVS formalism

Complex physical systems have been studied for many years using different approaches. Skyscraper building heights are restricted by the design limitations of their elevator systems. Long cable elevator systems will cause stretch because of their own weight. A newer technology is electromagnetic elevators that are able to travel in three dimensions and have no limitation on their height. M&S (Modeling and Simulation) methodologies and tools provide means for cost-effective validity analysis for designing complex physical and mechanical systems. Cell-DEVS is a formal methodology for cell-divided models based on DEVS (Discrete Event System Specifications) formalism. In this work, a cellular simulation model is used to model a three dimensional elevator system in a tall building with huge occupied area. The model defines appropriate rules for cells to control the elevators moving in different directions, while applying certain regulations to their movement to avoid collisions. Path finding and collision avoidance strategies are used to simulate an applicable system. We present the elevator model specifications, simulation design and discuss different simulation scenarios.

Cable-anchor robot implementation using embedded CD++

We show the design and implementation of a robot controller with a unique locomotion system. We demonstrate that a discrete-event simulation based design provides a cost-effective, flexible, open workflow for modular robotic development. The robot is designed to translate against a vertical surface using cables fixed at one end that can wind on motor-controlled spools attached to the robot. This architecture was implemented first as a regressively tested simulation within CD++ then ported to Real-time CD++. Using the NXT++ interface library, a hardware implementation of the robot using Lego® Mindstorms™ was shown to be controllable.

Flight dynamics and surveillance equipment simulation for trajectory based operation in unmanned aerial systems

This paper presents a Research and Development (R&D) effort to design and develop a flight simulation system with Adaptive Surveillance Broadcast (ADS-B), and Traffic Collision Avoidance System (TCAS), for integration of Unmanned Aerial Systems (UAS) into National Airspace System (NAS). The paper will delineate the design and development of the Next Generation Applied Research (NEAR) Labs FMS (NEAR-FMS) including the UAS aircraft models, and the surveillance simulation equipment. The NEAR-FMS will be used in NextGen projects such as Four-Dimensional Trajectory 4DT operations, as well as Alliance for System Safety of UAS through Research Excellence (ASSURE) projects funded by Federal Aviation Association (FAA). Middle-fidelity Flight Dynamic Models (FDM) of two UASs, a Predator class and a Global Hawk have been designed and tested on JSBSim aerodynamic simulator. Autopilots have been designed and implemented for both UAS FDMs. The paper will present the results of tests on the UAS simulated flights and performance data. The UAS models will be used to test the criticality of the conventional surveillance equipment of the UASs as well as identifying the requirements of these systems for such aircraft. Finally, the assessment of the data generated by the simulated flights will drive the requirements and constraints on the conventional surveillance equipment on the UAS. This project is a work in progress and the detailed results will be published in future publications.