• 제목/요약/키워드: 근사 기법

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Phase Noise Compensation in OFDM Communication System by STFBC Method (OFDM 통신 시스템에서 STFBC 기법을 이용한 위상잡음 보상)

  • Li Yingshan;Ryu Heung-Gyoon;Jeong YoungHo
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.16 no.10 s.101
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    • pp.1043-1049
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    • 2005
  • In OFDM system suitable for high capacity high speed broadband transmission, ICI caused by phase noise degrades system performance seriously by destroying the orthogonality among subcarriers. In this paper, a new STFBC method combining ICI self cancellation scheme and antenna, time, frequency diversity is studied to reduce ICI effectively. CPE and ICI are analyzed by the phase noise linear approximation method in the proposed STFBC OFDM system. CIR, PICR and BER are discussed to compare the system performance degraded by phase noise of PLL. As results, STFBC method significantly reduces ICI. Furthermore, the SCI that usually happens in the traditional STBC, SFBC diversity coding method can be easily avoided.

Equivalent Linear Stiffness Matrix of Pile Foundation for the Seismic Response Analysis of Bridges (교량의 지진응답해석을 위한 말뚝기초의 등가 선형 강도행렬)

  • 박형기;조양희
    • Journal of the Earthquake Engineering Society of Korea
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    • v.5 no.3
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    • pp.1-8
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    • 2001
  • Seismic design forces for bridge components may be determined by modifying elastic member forces of design earthquakes using appropriate response modification factors according to the national design code of bridges Modeling technique of pile foundation system is one of the important parameters which greatly affects the results in the process of the elastic seismic analysis of a bridge system with pile foundation. In this paper, a approximate and simplified modeling technique of a pile foundation system for the practical purposes is presented. The modeling technique is based on the stiffnesses of pile foundation during earthquake. The horizontal stiffnesses are determined from the resistance-deflection curves derived from the results of dynamic field tests using cyclic loads and the vertical stiffness includes the effects of the end bearing capacities and side friction of piles as well as the pile compliances under the expected vertical load level. The applicability of the proposed technique has been validated through the some example bridge analyses.

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A Numerical Analysis of the Shallow Water Equations Using the Multi-slope MUSCL (다중 경사 MUSCL을 이용한 천수방정식의 수치해석)

  • Hwang, Seung-Yong;Lee, Sam-Hee
    • Proceedings of the Korea Water Resources Association Conference
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    • 2011.05a
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    • pp.158-158
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    • 2011
  • 천수방정식과 같은 쌍곡선형 미분방정식의 불연속 해에 대한 Riemann 해법은, 1950년대 말 공기동역학 분야에서 S. K. Godunov의 선구적인 시도 이후, 다양한 영역에서 성공적으로 적용되고 있다. 당초 제안된 해법은 공간에 대해 1차 정도였으나, 2차의 정도를 얻을 수 있는 기법이 1970년대 말 B. van Leer에 의해 제안되었으며, MUSCL로 불린다. 서로 인접한 격자의 보존변수가 고려된 경사가 도입되어 두 격자에 의해 공유되는 변의 좌 우에서 선형으로 보존변수가 재구축되는 MUSCL은 제한자와 함께 이용될 때, 구조 격자 체계에서 비교적 단순하면서도 효과적인 적용성이 입증되었다. 그런데, 이 기법을 2차원의 비구조 격자 체계에 적용하는 경우, 인접한 모든 격자의 보존변수를 고려한 평면의 경사를 결정해야 하는 어려움이 따른다. 특히, 삼각형 비구조 격자에 적용할 경우 최적의 평면을 결정하기 위해 Green-Gauss 적분식이나 최소-자승법 등을 이용하게 된다. 이에 비해, 2010년 T. Buffard와 S. Clain이 제안한 다중경사 기법은 격자의 각 변에서 경사가 각각 결정되는 방법으로 계산량이 많은 Green-Gauss 적분식이나 최소자승법을 피할 수 있는 장점이 있는 것으로 알려져 있다. 정확해가 알려진 두 경우에 대해 몇 가지 제한자를 적용한 결과를 1차 정도의 해와 함께 비교하였으며, superbee 제한자에 의한 결과가 우수하였으나, 희유파와 충격파가 맞닿는 곳에서 수치 분산이 나타났다. minmod 제한자의 결과가 대체로 무난하였으며, 이를 2차원 댐 붕괴 문제에 적용하여 1차 정도의 해와 비교하였다. 마찰이 없고 초기 수심이 댐 상류에서 10 m, 하류에서 5 m로서 물이 차 있는 경우, 1차 정도의 해에서 나타나는 수치 소산이 2차 정도에서는 발생되지 않았다. 댐 하류에서 초기에 수심이 영으로 바닥이 드러난 경우에서 마찰의 영향을 검토하였다. 마찰이 있는 경우, 마찰 경사 항의 Manning 계수를 0.04로 두었으며, 마찰에 의한 영향이 잘 드러났다. 수심이 50 mm 보다 작은 경우에는 마찰을 적용하지 않았다. 이 연구는 환경부 '차세대 핵심환경기술개발 사업'의 지원에 의한 것이다.

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A Comparative Study on Finite Difference Method and Finite Analytic Method to One-Dimensional Convective-Diffusion Equation (1차원 이류·확산 방정식에 대한 유한차분법과 유한해석법의 비교연구)

  • Choi, Song Yeol;Cho, Won Cheol;Lee, Won Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.3
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    • pp.129-138
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    • 1993
  • In this study, the applicability of finite analytic method (FAM) is studied by selecting linearized-Burgers equation and Burgers equation which have convective and diffusive behaviors as the model equation of Navier-Stokes equations and by comparing numerical solution of finite difference method (FDM) and finite analytic method. The results are as follows. It is shown that the convergence of FAM for steady-state analytic solution of linearized-Burgers equation and Burgers equation is better than that of FDM under the same criteria. Also the accuracy of FAM for transient solution of Burgers equation is excellent. Especially, it is shown that oscillation phenomenon due to dispersion errors which occur according to the choice of grid size in FDM does not occur in FAM at all. So, it can be thought that FAM is numerically very stable scheme, which is free from dispersion errors.

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Numerical Analysis Method of Overlay Model for Material Nonlinearity Considering Strain Hardening (변형률 경화를 고려한 오버레이 모델의 재료비선형 수치해석기법)

  • Baek, Ki Youl
    • Journal of Korean Society of Steel Construction
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    • v.19 no.3
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    • pp.291-301
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    • 2007
  • The overlay model is a certain kinds of numerical analysis method to present the material non-lineariy which is represented the baushinger effect and the strain hardening. This model simulates the complex behavior of material by controlling the properties of the layers which like the hardening ratio, the section area and the yield stress. In this paper, the constitutive equation and plastic flow rule of each layer which are laid in the plane stress field are obtained by using the thermodynamics. Two numerical examples were tested for the validity of proposed method in uniaxial stress and plane stress field with comparable experimental results. The only parameter for the test is the yield stress distribution of each layers.

One-Way Delay Estimation and Its Application (단방향 지연 시간 추정 기법과 이를 이용한 응용)

  • Choi Jin-Hee;Yoo Hyuck
    • Journal of KIISE:Information Networking
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    • v.32 no.3
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    • pp.359-369
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    • 2005
  • Delay estimation is a difficult Problem in computer networks. Accurate one-way delay estimation is crucial because it serves a very important role in network performance and thus application design. RTT(Round Trip Time) is often used as an approximation of the delay, but because it is a sum of the forward and reverse delays, the actual one-way delay cannot be estimated accurately from RTT. To estimate one-way delay accurately, this paper proposes a new scheme that analytically derives one-way delay, forward and reverse delay respectively. We show that the performance of TCP can improve dramatically in asymmetric networks using our scheme. A key contribution of this paper is that our one-way deiay estimation is much more accurate than RTT estimation so that TCP can quickly find the network capacity in the slow start phase. Since RTT is the sum of the forward and reverse delays, our scheme can be applied to any protocol that is based on RTT.

Preliminary Design for Axisymmetric Supersonic Inlet using Conical Flow Solution and Optimization Technique (원추 유동 해와 최적화 기법을 이용한 축대칭 초음속 흡입구의 예비 설계)

  • 정석영
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.9
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    • pp.11-19
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    • 2006
  • Design program was developed to determine the external shape of the supersonic axisymmetric inlet by combining conical flow solver and approximation technique of conical shock with gradient-based optimization algorithm. Inlet designs were carried out under various operation conditions through optimization with respectively two object functions which consist of pressure recovery and cowl drag and with constraints about shock position, cowl shape, and minimum throat area. New object function consisting of pressure recovery and drag of the external cowl was proposed and the optimized shapes from new object function were compared to the ones from the old object function which maximize only the pressure recovery. Through computations of inviscid and turbulent flow, was tested performance of the design program and performance estimated in design program agreed well with computation results for inlets designed under various flight conditions.

Performance Evaluation of Channel Estimation using Trigonometric Polynomial Approximation in OFDM Systems with Transmit Diversity (송신 다이버시티를 가진 OFDM 시스템에서 삼각다항식 근사화를 이용한 채널 추정 기법의 성능평가)

  • 이상문;최형진
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.3C
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    • pp.248-256
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    • 2003
  • Space-time coding was designed for an efficient transmit diversity technique to improve performance of wireless communication. For the transmit diversity using space-time coding, the receiver requires to estimate channel parameters corresponding to each transmit antennas. In this paper, we propose an efficient channel estimation scheme based on trigonometric polynomial approximation in OFDM systems with transmit diversity using space-time coding. The proposed scheme is more efficient than the conventional scheme in terms of the computational complexity. For QAM modulation, when the size of FFH is 128, the conventional scheme with significant tap caching of 7 requires 9852 complex multiplications for TU, HT and BU channels. But the proposed scheme requires 2560, 7680 and 3584 complex multiplications for TU, HT and BU channels, respectively. Especially, for channels with smaller Doppler frequency and delay spreads, the proposed scheme has the improved BER performance and complexity. In addition, we evaluate the performance of maximum delay spread estimation in unknown channel. The performance of the proposed scheme is investigated by computer simulation in various multi-path fading environments.

A Real-time Particle Filtering Framework for Robust Camera Tracking in An AR Environment (증강현실 환경에서의 강건한 카메라 추적을 위한 실시간 입자 필터링 기법)

  • Lee, Seok-Han
    • Journal of Digital Contents Society
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    • v.11 no.4
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    • pp.597-606
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    • 2010
  • This paper describes a real-time camera tracking framework specifically designed to track a monocular camera in an AR workspace. Typically, the Kalman filter is often employed for the camera tracking. In general, however, tracking performances of conventional methods are seriously affected by unpredictable situations such as ambiguity in feature detection, occlusion of features and rapid camera shake. In this paper, a recursive Bayesian sampling framework which is also known as the particle filter is adopted for the camera pose estimation. In our system, the camera state is estimated on the basis of the Gaussian distribution without employing additional uncertainty model and sample weight computation. In addition, the camera state is directly computed based on new sample particles which are distributed according to the true posterior of system state. In order to verify the proposed system, we conduct several experiments for unstable situations in the desktop AR environments.

Real-Time Simulation of Single and Multiple Scattering of Light (빛의 단일 산란과 다중 산란의 실시간 시뮬레이션 기법)

  • Ki, Hyun-Woo;Lyu, Ji-Hye;Oh, Kyoung-Su
    • Journal of Korea Game Society
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    • v.7 no.2
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    • pp.21-32
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    • 2007
  • It is significant to simulate scattering of light within media for realistic image synthesis; however, this requires costly computation. This paper introduces a practical image-space approximation technique for interactive subsurface scattering. We use a general two-pass approach, which creates transmitted irradiance samples onto shadow maps and computes illumination using the shadow maps. We estimate single scattering efficiently using a method similar to common shadow mapping with adaptive deterministic sampling. A hierarchical technique is applied to evaluate multiple scattering, based on a diffusion theory. We further accelerate rendering speed by tabulating complex functions and utilizing level of detail. We demonstrate that our technique produces high-quality images of animated scenes with blurred shadow at hundreds frames per second on graphics hardware. It can be integrated into existing interactive systems easily.

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