• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.4
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• pp.3-8
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• 2013

In CDMA-based systems, recently, researches on chip-level equalization have been studied in order to improve receiving performance when supporting high-rate data services. In this paper, we consider a chip-level LMMSE (linear minimum mean-squared error) receiver for D-TxAA (dual stream transmit antenna array) based single stream HSDPA MIMO systems using precoding weights. First, we will derive precoding weights for maximizing the total instantaneous received power. We will also analyze the effects of both transmit delay of precoding weights and mobile velocity on chip-level LMMSE receivers, which is verified through computer simulations in various mobile channel environments.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.258-262
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• 2004

The uncertainty of the detector-based candela scale is limited by the area measurement uncertainty of radiometric apertures. The apertures were fabricated with a diamond-turning machine which trimmed the edge of the apertures as sharply as a knife edge. The positions of the apertures were controlled by a digital feedback algorithm to scan the laser spot with the beam waist less than 5 ${\mu}{\textrm}{m}$. The knife edge scan yielded a set of coordinates on the edges of the aperture. The areas of the apertures were obtained by fitting the coordinates to the ellipses. The relative standard uncertainty of the measurement was estimated to be 8${\times}$10$^{-5}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1499-1509
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• 2000

In this paper, we propose an efficient channel estimation technique for space-time coded orthogonal frequency-division multiplexing (OFDM) systems with transmitter and receiver diversity. The proposed technique estimates uniquely all channel frequency responses needed in a decoder of space-time coded OFDM systems using "comb-type" raining symbols. The computational complexity of the proposed technique is reduced dramatically, compared with the previous minimum mean-squared error (MMSE) technique, due to the processing is made all in the frequency-domain. Also, several other techniques for mitigating random noise effect and tracking channel variation are discussed to further improve the performance of the proposed approach. The performances of the proposed approach are demonstrated by computer simulation for mobile wireless channels. channels.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1007-1011
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• 2006

본 연구에서는 어류 생태계 유지를 위해 필요한 생태학적 추천유량을 산정하고, 어류의 서식처 환경인 여울과 웅덩이의 형성조건을 검토함으로써 '작용'인 '흐름'과 '응답'인 '하상구조'와의 상관 관계를 규명하고자 하였다. 본 연구의 대상하천인 금호강에서는 하상변동이 활발한 자연 상태를 벗어나 하상의 이동성 상당히 둔화된 상태이며, 저수로내 여울과 웅덩이도 대표어종이 서식할 수 있는 자갈하상 구조에 변화가 일어나고 있는 것으로 분석되었다. 이것은 금호강 상류에 영천댐 건설의 영향이 어느 정도 미치고 있음을 유황분석 결과를 통해 간접적으로 파악할 수 있었다. 댐과 같은 수공구조물의 건설로 인하여 하도가 고정화된 상태에서 장기간에 걸치게 되면 여울과 웅덩이와 같은 하상구조가 축소되거나 소멸되어 금호강에서의 대표어종 서식처 환경에 영향을 미칠 것으로 추정된다. 금번 연구결과, 금호강에서 어류의 생식에 필요한 생태학적 추천유량 $8.2m^3/sec$가 필요하였으며, 어류의 서식처 환경인 여울과 웅덩이를 지속적으로 유지되기 위해서는 $250m^3/sec$ 이상의 유량이 연간 한번 이상 흘러야 하고, 2.5년 내지 3년 마다 약 $500m^3/sec$ 정도의 유량이 흐를 필요가 있다고 분석되었다. 본 연구 대상지점에서 흐름과 하상구조를 하천생태계와 연계해서 볼 때, 생태추천유량은 어디까지나 대표어종이 서식할 수 있는 최소조건에 불과하다. 대표어종이 장기간에 걸쳐 서식할 수 있는 하상구조가 존재하기 위해서는 대표어종이 선호하는 여울과 웅덩이가 필요하다. 결국 대표어종이 서식하기 위한 필요충분조건은 생태추천유량 확보와 아울러 대표어종이 선호하는 하상구조를 유지하기 위해서는 하도의 이동성을 유발할 유황변화가 필요하다는 것이 입증되었다.대상으로 연중 발생하는 큰 호우사상에 대해 임의의 강우관측소를 결측지점으로 가정하고 주변의 강우관측소로부터 각각의 방법을 이용해 가중치들을 산정하여 결측지점의 강우량 값을 보정하고자 하였다. 또한 각각의 방법을 이용하여 얻어진 결과에 대해 실측값과 보정값의 오차정도를 평균절대오차법(Mean Absolute Error)과 제곱평균제곱근오차법(Root Mean Squared Error)에 의해 산정하여 보정 방법간의 효율성을 검토하고자 하였다.9년, 그리고 2010년${\sim}$2019년까지 총 4구간으로 나누어 결과를 도출하였으며 예상한 바와 같이 후반기 20년 동안에 세 가지 지표가 취약해 지는 것을 확인할 수 있었고, 특히 2000년부터 2009년까지 10년 동안에는 더욱 취약해짐을 확인할 수 있었다.를 보임에 따라 그 정책적 효과는 때로 역기능적인 결과로 초래하였다. 그럼에도 불구하고 이 연구결과를 통하여 최소한 주식시장(株式市場)에서 위탁증거금제도는 그 제도적 의의가 여전히 있다는 사실이 확인되었다. 또한 우리나라 주식시장에서 통상 과열투기 행위가 빈번히 일어나 주식시장을 교란시킴으로써 건전한 투자풍토조성에 저해된다는 저간의 우려가 매우 커왔으나 표본 기간동안에 대하여 실증분석을 한 결과 주식시장 전체적으로 볼 때 주가변동율(株價變動率), 특히 초과주가변동율(超過株價變動率)에 미치는 영향이 그다지 심각한 정도는 아니었으며 오히려 우리나라의 주식시장은 미국시장에 비해 주가가 비교적 안정적인 수준을 유지해 왔다고 볼 수 있다.36.4%)와 외식을 선호(29.1%)${\lrcorner}$ 하기 때문에 패스트푸드를 이용하게 된 것으로 응답 하였으며, 남 여 대학생간에는 유의한 차이(p<0.05)가 인정되었다. 응답자의 체형은 ${\ulco

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.341-353
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• 2014

In order to deliver a centimeter-level kinematic positioning solution with GPS carrier-phase measurements, it is prerequisite to use correctly resolved integer ambiguities. Based on the mathematical modeling of GPS network with application of its geometrical constraints, this research has investigated an instantaneous ambiguity resolution procedure for the so-called 'integer constrained least-squares' technique which can be effectively implemented in real-time structure monitoring. In this process, algorithms of quality control for the float solutions and hypothesis tests using the constrained baseline for the ambiguity validation are included to enhance reliability of the solutions. The proposed procedure has been implemented by MATLAB, the language of technical computing, and processed field trial data obtained at a cable-stayed bridge to access its real-world applicability. The results are summarized in terms of ambiguity successful rates, impact of the stochastical models, and computation time to demonstrate performance of the instantaneous ambiguity resolution proposed.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.2
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• pp.51-60
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• 2010

This paper proposes a new scheme to obtain enhanced 3D shape information rapidly for WLPSI(White Light Phase Shifting Interferometry). WLPSI is a convenient method to measure the height of the micro products. First we propose an effective method of limiting search interval for detecting the peak of the visibility function in order to obtain 3D shpae information rapidly. Second we propose an automatic base level decision method basad on image processing and a correction algorithm using the least square approximation method to overcome the global tilt problem of the conventional WLPSI algorithms. Third we propose an adaptive filtering method to remove the distortion known as bat-wing effect which appears near the step discontinuity. Experimental results show that the proposed overall technique is fast and provides more enhanced 3D shape information compared with the conventional WLPSI algorithms.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.335-341
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• 2009

In this paper, review of developed MLS-based finite elements and a proposal for their applications are described. The shape functions and their derivatives of MLS-based finite elements are constructed using Moving-Least Square approximation. In MLS-based finite element, using the adequate influence domain of weight function used in MLS approximation, kronecker delta condition could be satisfied at the element boundary. Moreover, because of the characteristics of MLS approximation, we could easily add extra nodes at an arbitrary position in MLS-based finite elements. For these reasons, until now, several variable-node elements(2D variable element for linear case and quadratic case and 3D variable-node elements) and finite crack elements are developed using MLS-based finite elements concept. MLS-based finite elements could be extended to 2D variable-node triangle element, 2D finite crack triangle element, variable-node shell element, finite crack shell element, and 3D polyhedron element. In this paper, we showed the feasibility of 3D polyhedron element at the case of femur meshing.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.1
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• pp.17-26
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• 2014

This paper presents a dynamic crack propagation algorithm based on the Moving Least Squares(MLS) difference method. The derivative approximation for the MLS difference method is derived by Taylor expansion and moving least squares procedure. The method can analyze dynamic crack problems using only node model, which is completely free from the constraint of grid or mesh structure. The dynamic equilibrium equation is integrated by the Newmark method. When a crack propagates, the MLS difference method does not need the reconstruction of mode model at every time step, instead, partial revision of nodal arrangement near the new crack tip is carried out. A crack is modeled by the visibility criterion and dynamic energy release rate is evaluated to decide the onset of crack growth together with the corresponding growth angle. Mode I and mixed mode crack propagation problems are numerically simulated and the accuracy and stability of the proposed algorithm are successfully verified through the comparison with the analytical solutions and the Element-Free Galerkin method results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1C
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• pp.102-109
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• 2008

The higher data rate of mobile communications has been required for various multimedia services. In DS-CDMA system, one of the solutions to increase the throughput is to use multicode. However, multipath channel destorys the orthogonality of spreading codes, which causes the intercede interference(ICI). ICI gives severe effect on multicode DS-CDMA for BER performance. Conventionally, multicode DS-CDMA system uses the Rake receiver with turbo code, which cannot overcome error floor caused by ICI. In this paper, we propose frequency domain turbo equalization based on minimum mean squared error(FDTE-MMSE) for multicode DS-CDMA in frequency selective channel and evaluate its BER performance by computer simulation. The simulation results show that FDTE-MMSE gives much better performance in high Eb/N0 than the Rake receiver with turbo code in multipath length L>1.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.7-12
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• 2019

Ambient backscatter communication is limited to channel estimation technique through a pilot signal, which is a channel estimation method in current RF communication, due to transmission power efficiency. In a limited transmission power environment, the research of traditional ambient backscatter communication has been studied assuming that it is an ideal channel without signal distortions due to channel conditions. In this paper, we propose an expectation-maximization(EM) algorithm, one of the blind channel estimation techniques, as a channel estimation method in ambient backscatter communication system which is the state of channel following normal distribution. In the proposed system model, the simulations confirm that channel estimate through EM algorithm is approaching the lower bound of the mean square error compared with the Bayesian Cramer-Rao Boundary(BCRB) to check performance. It shows that the channel parameter can be estimated in the ambient backscatter communication system.