• Journal of the Korea Society for Simulation
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• v.1 no.1
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• pp.64-76
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• 1992

The DEVS(discrete event system specificaition) formalism specifies a discrete event system in a hierarchical, modular form. DEVSIM++ is a C++based general purpose DEVS abstract simulator which can simulate systems modeled by the DEVS formalism in a sequential environment. This paper describes P-DEVSIM++which is a parallel version of DEVSIM++ . In P-DEVSIM++, the external and internal event of DEVS models can by processed in parallel. For such processing, we propose a parallel, distributed optimistic simulation algorithm based on the Time Warp approach. However, the proposed algorithm localizes the rollback of a model within itself, not possible in the standard Time Warp approach. An advantage of such localization is that the simulation time may be reduced. To evaluate its performance, we simulate a single bus multiprocessor architecture system with an external common memory. Simulation result shows that significant speedup is made possible with our algorithm in a parallel environment.

• Journal of the Korea Society for Simulation
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• v.3 no.1
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• pp.125-134
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• 1994

In real-time database systems, transactions's commitment done before the given deadlines is more important than just getting the maximum throughput. Transactions missing the given deadlines are no longer meaningful in real-time applications. Therefore, there is a need for new transaction processing models to meet the given deadlines in real-time database applications, because moat conventional transaction models are not designed to meet deadlines. In this paper we propose a new transaction models which uses multiple versions of a data item. The model uses read-from graphs and dynamic reorder of transactions to meet deadlines. A read-from graph contains the past read semantics of read operations and support the model to decide which database operation to be taken. Then, we show simulation results comparing the proposed model with other transaction models such as two phase locking model and the optimistic concurrency control model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.287-288
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• 2007

• KIPS Transactions on Computer and Communication Systems
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• v.4 no.5
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• pp.147-152
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• 2015

In general, there are two synchronization methods in parallel event-driven simulation, pessimistic approach and optimistic approach. In this paper, we propose a new approach, sporadic synchronization combining both for prediction-based parallel event-driven logic simulation. We claim this hybrid solution is pretty effective to minimize both checkpoint overhead and restart overhead, which are related problems with frequent false predictions for improving the performance of the prediction-based parallel event-driven logic simulation. The experiment has clearly shown the advantage of the proposed approach.

• IE interfaces
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• v.20 no.3
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• pp.363-375
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• 2007

Under the fast technology changes and budget constraints, the organizations related to national defense face increased demands to develop innovative strategy and methodology to maximize performance with drastically reduced cost. In this context, the management of innovation and change in the defense acquisition area is vital to the Ministry of National Defense, related organizations and industries. In this paper, we discuss three comprehensive innovation strategies and methodologies for the defense acquisition area preparing for next-generation warfare; EVMS (earned value management system), PBL (performance based logistics) and SBA (simulation based acquisition). These collaborating innovative efforts enable us to tackle defense challenges for government and industries with a flexible and optimistic approach that maximizes productivity and performance with minimum cost.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.4
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• pp.9-17
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• 2010

The mobility of nodes are different in wireless ad hoc networks. Routes have to be refreshed frequently due to the mobility of the nodes acting as routers. Path consists of a few highly mobile nodes should be avoided to forward packets, because even only one highly mobile node may result in the break of path. We develop a mobility aware method to evaluate path stability for multipath routing in wireless Ad Hoc networks. Specifically, we extend it to a well-studied multipath routing protocol known as ad hoc on-demand multipath distance vector (AOMDV). The resulting protocol is referred to as path stability evaluation (PSE). Performance comparison of AOMDV with PSE are studied through ns-2. Simulation shows that PSE has optimistic results in performance metrics such as packet delivery, end-to-end delay, routing overhead and throughput.

• The Journal of Korea Robotics Society
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• v.4 no.2
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• pp.97-104
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• 2009

Recently, simultaneous localization and mapping (SLAM) approaches employing Rao-Blackwellized particle filter (RBPF) have shown good results. However, due to the usage of the accurate sensors, distinct particles which compensate one another are attenuated as the RBPF-SLAM continues. To avoid this particle depletion, we propose the strategic games to assign the particle's payoff which replaces the importance weight in the current RBPF-SLAM framework. From simulation works, we show that RBPF-SLAM with the strategic games is inconsistent in the pessimistic way, which is different from the existing optimistic RBPF-SLAM. In addition, first, the estimation errors with applying the strategic games are much less than those of the standard RBPF-SLAM, and second, the particle depletion is alleviated.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.553-556
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• 1998

The 1-D numerical model and its extraction methodology are suggested and these simulation results for the S-swing as a function of back-gate voltage are well matched with the measured. S-swing characteristics are analyzed using PD-SOI devices with enough deeper regions up to substrates. The PD-SOI device doesn't have to be short channel to see the anomalous subthreshold phenomena based on the back gate bias. This results recommend to operate better SOI device performances by controlling the back gate voltages. So SOI performances will be much optimistic with proper control of the back-gate voltage for the already- proven- high- performance (APHP) SOI VLSIs.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.3 no.3
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• pp.62-72
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• 2010

As the applications for Mobile Ad-hoc NETworks (MANETs) have varied, performance analysis has become one of the main research areas. They commonly offer only simple radio propagation models that neglect obstacles of a propagation environment. The radio wave propagation model has a strong impact on the results of the simulation run. In this paper we present the new experimental results of the impacts of the various propagation models on MANETs' performance. Intensive simulations have been presented using the group mobility which models typical ad-hoc situations such as military movements or disaster recovery activities under the supervision of a group leader. Comparisons of conventional simple models with more complicated models, i.e., shadowing, Raleigh, and Ricean models, show that, in spite of the models' popularity, the free space and two-ray ground models are too optimistic in describing real ad-hoc group mobility situations.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.9 no.3
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• pp.161-165
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• 2009

Increase of multimedia information in Web requires a new method to manage and service multimedia documents efficiently. This paper proposes a conceptual object grouping method by fuzzy filtering, which is automatically constituted based on increase of multimedia documents. The proposed method composes subsumption relations between conceptual objects automatically using fuzzy filtering of the document objects that are extracted from domains. Grouping of such conceptual objects is regarded as subsumption relation which is decided by $\mu$-cut. This paper proposes $\mu$-cut, FAS(Fuzzy Average Similarity) and DSR(Direct Subsumption Relation) to decide fuzzy filtering, which groups related document objects easily. This paper used about 1,000 conceptual objects in the performance test of the proposed method. The simulation result showed that the proposed method had better retrieval performance than those for OGM(Optimistic Genealogy Method) and BGM(Balanced Genealogy Method).