• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10C
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• pp.1469-1483
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• 2004

We propose a packet scheduling algorithms for streaming media. We assume that the receiver periodically reports back the channel throughput. From the original video data, the importance level of a video packet is determined by its relative position within its group of pictures, taking into account the motion-texture discrimination and temporal scalability. Thus, we generate a number of nested substreams. Using feedback information from the receiver and statistical characteristics of the video, we model the streaming system as a queueing system, compute the run-time decoding failure probability of a Same in each substream based on effective bandwidth approach, and determine the optimum substream to be sent at that moment in time. Since the optimum substream is updated periodically, the resulting sending order is different from the original playback order. From experiments with real video data, we show that our proposed scheduling scheme outperforms the conventional sequential sending scheme.

• The KIPS Transactions:PartB
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• v.12B no.4 s.100
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• pp.379-386
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• 2005

This paper provides a rigorous theory for analysis of quantization effects and optimum filter bank design in quantized multidimensional subband filter banks. Even though subband filter design has been a hot topic for last decades, a few results have been reported on the subband filter with a quantizer. Each pdf-optimized quantizer is modeled by a nonlinear gain-plus-additive uncorrelated noise and embedded into the subband structure. Using polyphase decomposition of the analysis/synthesis filter banks, we derive the exact expression for the output mean square quantization error. Based on the minimization of the output mean square error, the technique for optimal filter design methodology is developed. Numerical design examples for optimum nonseparable paraunitary and biorthogonal filter banks are presented with a quincunx subsampling lattice. Through the simulation, $10\~20\;\%$ decreases in MSE have been observed compared with subband filter with no quantizers especially for low bit rate cases.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.349-354
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• 2004

As a transmitter sub-assembly in the XFP(10 Gb/s Small Form Factor Pluggable) transceiver module, a transmitter optical sub-assembly(TOSA) is designed, fabricated and characterized in view of electrical and thermal performances. For a low-cost and compact packaging TOSA, the bias-tee and the matching resistor are monolithically integrated on the AlN sub-mount and a newly designed coplanar waveguide is drawn in the TO-stem. All optoelectronic components packaged in the TOSA are modeled by the equivalent circuit, which helps to improve and characterize the TOSA performance. The fabricated TOSA shows the -3㏈ bandwidth as high as 11 GHz at an elevated temperature of 85$^{\circ}C$.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.74-79
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• 2008

The fracture strength of cross groove type constant velocity joint is largely determined by the fracture strength of the cage having window-like pockets for retaining the torque transmitting balls. A stress distribution acting on the cage is influenced by rigidities of the rim portion and of the column members, therefore requires a calculation such as FEA. To analyze fracture strength of cage, a 3-D elasto-plastic finite element analysis and a submodeling technique are used to achieve both computational efficiency and accuracy. The results are in reasonably good agreement with experiment.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.234-238
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• 2015

When we use a Finite Elements Method (FEM) to solve a linear static analysis problem, number of elements need to be sufficiently small for convergence of the solution. If we analysis a part, whose curvature is varying heavily, we face to determine how small the elements size is, because the calculated stress is increased as the elements are smaller. In this case, we need to analysis with mesh insensitive method, stress linearization. We can get a solution that is not varying with the elements size if the size is smaller than a certain level. In this paper, we evaluate a pressure vessel having geometrical discontinuities using stress linearization. First, we analysis the vessel with global model, including all part of the vessel, using large shell elements. Second, we analysis the local part of the vessel, which is the small part occurring maximum stress, using small continuum elements. Last, we evaluate the safety of the pressure vessel according to the ASME Sec. VIII Div 2.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.326-327
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• 2020

본 논문은 비대칭 모듈형 멀티레벨 토폴로지를 이용한 컨버터 기반 발전원의 실계통 연계에 대한 실시간 시뮬레이터 모의를 수행하였다. 비대칭 모듈형 멀티레벨 컨버터를 구성하는 6개의 암은 직렬로 연결된 다수의 하프브릿지와 풀브릿지 서브모듈로 구성되어 있으며, 각각의 서브모듈을 서로 다른 전압으로 제어하여 출력품질을 극대화 할 수 있다. 본 실험에서 사용된 실계통 및 비대칭 모듈형 멀티레벨 컨버터는 Real-Time Digital Simulator (RTDS)의 RSCAD를 이용하여 모델링 하였으며, 해당 계통 내 컨버터 기반 발전원들의 응답을 결과로 다룰 것이다.

• Journal of KIISE:Computing Practices and Letters
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• v.12 no.2
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• pp.129-140
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• 2006

The existing CBD development methods deal with the analysis phase in a superficial manner. Applying such a superficial analysis to business applications with a number of subsystems makes analysis models be inconsistent with levels and styles, only depending on experiences of the analysts. This inconsistent analysis might cause more serious problems during the subsequent development phases, resulting in the failure of the projects. In this paper, we propose a rule-based analysis pattern that provides an analysis template for business applications. This pattern analyzes the concepts of business applications by using external events and internal rules that process the events. Employing this pattern, a huge business application can be developed by a couple of co-analysts who work together in a consistent and systematic manner. This paper also describes an efficient way to develop business components with the suggested analysis pattern using banking deposit case study through UML Components development process.

• Aerospace Engineering and Technology
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• v.2 no.1
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• pp.140-152
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• 2003

Scenario is a guiding principle of launch operation and control for rocket and ground support system. Therefore, developing a scenario is the first step to prepare for rocket launch, which is a critical task for success of KSR-III flight test. The launch scenario for KSR-III flight test is a procedural sequence of command and control signals to be given to rocket and ground support systems. In this paper, the UML object modeling method is applied to development of a launch scenario. First, the subsystems of the launch system are modeled by objects, and then the interfaces between each two subsystems are modeled by association links. The finally obtained object diagram of KSR-III launch system is used to analyzing flow of data and commands and control signals, and interactions. The scenario includes the sequences of pre-launch/launch operations and emergency operations.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.43-49
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• 1997

Generally, echo cancelers of a TV conference system or a audio conference system are to carry out a real time processing in the case of the closed room having long reverberation time because the system requires much time to modify filter coefficients to environmental changes. Therefore this paper proposes a new subband adaptive filtering method using polyphase filter banks of MPEG(Moving Picture Experts Group) audio system to solve the problems. This method divides signal spectra of input and output into several frequency bands, and each band is adaptively filtered by using ES-NLMS (Exponential Step-Normalized Least Mean Square) algorithm. The optimal number of subband is determined by computational simulations. According to the results of simulation, ERLE of the subband model is 2dB smaller than general full band, calculation rate's of the subband model is decreased about 88%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.765-770
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• 2014

This paper describes the study on a method for improving the structural durability of bolted joints applied to a composite bogie frame. In this study, three bolted joints with and without inserts and screw threads were selected for determining the effect of the inserts, using experiment and analysis. The structural performances of the proposed bolted joints were compared and evaluated using the test method prescribed by the ASTM D5961 standard. The results revealed that the bolted joint having an insert shape without the screw thread offered improved durability for application to a composite bogie frame. Furthermore, the structural integrity of the frame comprising the bolted joints was evaluated using finite element analysis according to the JIS E 4207 standard. The Tasi-Wu and Von-Mises failure criteria were used for determining the failure of the composite structure and bolted joints, respectively. A sub-modeling technique was introduced for investigating the performance of the bolted joints in greater detail. The analysis results demonstrated that the Tasi-Wu failure index of the composite structure near the bolted joints was reduced by approximately one-half after applying an insert without the screw thread. This implies that the structural durability of the bolted joints of a composite bogie frame could be improved by using a metal insert without the screw thread.