A knowledge-based environment for hierarchical modelling and simulation.

Hierarchical, modular specification of discrete-event models offers a basis for reusable model bases and hence for enhanced simulation of truly varied design alternatives. This dissertation develops a knowledge-based environment for hierarchical modelling and simulation of discrete-event systems as the major part of a longer, ongoing research project in artificial intelligence and distributed simulation. In developing the environment, a knowledge representation framework for modelling and simulation, which unifies structural and behavioral knowledge of simulation models, is proposed by incorporating knowledge representation schemes in artificial intelligence within simulation models. The knowledge base created using the framework is composed of a structural knowledge base called entity structure base and a behavioral knowledge base called model base. The DEVS-Scheme, a realization of DEVS (Discrete Event System Specification) formalism in a LISP-based, object-oriented environment, is extended to facilitate the specification of behavioral knowledge of models, especially for kernel models that are suited to model massively parallel computer architectures. The ESP-Scheme, a realization of entity structure formalism in a frame-theoretic representation, is extended to represent structural knowledge of models and to manage it in the structural knowledge base. An advantage of the knowledge-based environment is that it is capable of automatically synthesizing hierarchical, modular models from model base resident components defined by the extended DEVS-Scheme under the direction of structural knowledge using the extended ESP-Scheme. Since both implementation and the underlying LISP language are accessible to the user, the result is a medium capable of combining simulation modelling and artificial intelligence techniques. To show the power of the environment, modelling and simulation methodology in the environment are presented using an example of modelling a hypercube computer architecture. Applications of the environment to knowledge-based computer systems design, communications network design, and diagnostic expert systems design are discussed. Since structure descriptions in the environment are susceptible to run-time modification, the environment provides a convenient basis for developing variable family and variable structure simulation models such as adaptive computer architectures. Thus, the environment represents a significant step toward realizing powerful concepts of system-theoretic based formalisms. The environment also serves as a medium for developing distributed simulation architectures for hierarchical, modular discrete-event models

Trace-driven Rapid Pipeline Architecture Evaluation Scheme for ASIP Design

This paper proposes a rapid evaluation scheme of pipeline architecture using phase-accurate simulation with only delay model and trace. With latency information for every stage, we can decide if an instruction in one stage can proceed to the next stage or if an instruction can be issued for each cycle without evaluating the value for registers. Branch target becomes available with trace generated by fast instruction set simulation. Fast verification time becomes possible because instruction set simulation is performed only once. I

A Heterogeneous Distributed Simulation Framework Based on DEVS Formalism

This paper proposes a heterogeneous distributed simulation framework based on the DEVS formalism. A software bus called the DEVS bus is proposed, which virtually connects the DEVS models and conventional non-DEVS models developed by different simulation languages such as SIMAN, SLAM, SIMSCRIPT, and so on. For the DEVS bus protocol, the hierarchical simulation algorithm proposed by Zeigler is used. For communicating between DEVS models and nonDEVS models connected on the DEVS bus, a protocol converter is proposed. The converter is realized by transformation of non-DEVS models into an equivalent DEVS models at the I/O level. 1 Introduction Parallel and distributed discrete event simulation (PDES) [1] has been widely studied as a promising technology. PDES has been mainly concentrated on how to achieve reasonable speedup while guaranteeing that events are processed in chronological order by using a synchronization algorithm. PDES has been conventionally developed in homogeneous simulatio..

Analysis of the Effect of UTI-UTC to High Precision Orbit Propagation

As the spatial resolution of remote sensing satellites becomes higher, very accurate determination of the position of a LEO (Low Earth Orbit) satellite is demanding more than ever. Non-symmetric Earth gravity is the major perturbation force to LEO satellites. Since the orbit propagation is performed in the celestial frame while Earth gravity is defined in the terrestrial frame, it is required to convert the coordinates of the satellite from one to the other accurately. Unless the coordinate conversion between the two frames is performed accurately the orbit propagation calculates incorrect Earth gravitational force at a specific time instant, and hence, causes errors in orbit prediction. The coordinate conversion between the two frames involves precession, nutation, Earth rotation and polar motion. Among these factors, unpredictability and uncertainty of Earth rotation, called UTI-UTC, is the largest error source. In this paper, the effect of UTI-UTC on the accuracy of the LEO propagation is introduced, tested and analzed. Considering the maximum unpredictability of UTI-UTC, 0.9 seconds, the meaningful order of non-spherical Earth harmonic functions is derived