• Journal of Communications and Networks
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• 제7권4호
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• pp.450-461
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• 2005

In this paper, we derive analytical expressions for the exact pairwise error probability (PEP) of a space-time coded system operating over spatially correlated fast (constant over the duration of a symbol) and slow (constant over the length of a code word) fad­ing channels using a moment-generating function-based approach. We discuss two analytical techniques that can be used to evaluate the exact-PEPs (and therefore, approximate the average bit error probability (BEP)) in closed form. These analytical expressions are more realistic than previously published PEP expressions as they fully account for antenna spacing, antenna geometries (uniform linear array, uniform grid array, uniform circular array, etc.) and scattering models (uniform, Gaussian, Laplacian, Von-mises, etc.). Inclusion of spatial information in these expressions provides valuable insights into the physical factors determining the performance of a space-time code. Using these new PEP expressions, we investigate the effect of antenna spacing, antenna geometries and azimuth power distribution parameters (angle of arrival/departure and angular spread) on the performance of a four-state QPSK space-time trellis code proposed by Tarokh et al. for two transmit antennas.

• Journal of Communications and Networks
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• 제10권1호
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• pp.44-54
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• 2008

In this paper, an iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation using a posteriori probability (APP) demodulator is investigated. Two approaches of different complexity based on linear prediction are presented to utilize the temporal correlation of fading for the APP demodulator. The first approach intends to take account of all possible previous symbols for linear prediction, thus requiring an increase of the number of trellis states of the APP demodulator. In contrast, the second approach applies Viterbi algorithm to assist the APP demodulator in estimating the previous symbols, hence allowing much reduced decoding complexity. These two approaches are found to provide a trade-off between performance and complexity. It is shown through simulation that both approaches can offer significant BER performance improvement over the conventional differential detection under both correlated slow and fast Rayleigh flat-fading channels. In addition, when comparing the first approach to a modified bit-interleaved turbo coded differential space-time modulation counterpart of comparable decoding complexity, the proposed decoding structure can offer performance gain over 3 dB at BER of $10^{-5}$.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2011년도 춘계학술대회
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• pp.539-542
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• 2011

본 논문에서는 무선 통신 시스템의 시변 공간 상관 채널 (time-varying and spatially correlated channel) 환경에서 전송 시공간 부호 및 단순 선형 복조 처리 방식(transmit space-time code and simple linear decoding processing)으로 구성된 $2{\times}1$ Alamouti scheme의 성능을 분석한다. Alamouti 구조의 closed-form 확률밀도함수 (probability density function, PDF), 출력 신호 대 잡음 비(output signal-to-noise ratio, SNR) 및 오수신 확률 (outage probability)을 시간영역에서의 상관관계가 없음을 가정하고 공간 상관 계수(spatial correlation coefficient)의 함수로 유도한다. 이로써 채널 환경이 시변 공간 상관 (time-varying and spatially correlated)된 경우, Alamouti 구조의 성능은 상당히 열화 됨을 확인할 수 있다.

• 한국지역지리학회지
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• 제17권4호
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• pp.432-442
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• 2011

기온, 강수와 같은 기후관측 자료들은 공간과 더불어 시간적인 변이를 동시에 나타낸다. 따라서 신뢰성 높은 시계열 분포도 작성을 위해 공간적 자기상관성만을 고려하는 기존 공간 내삽 기법에 시공간적 자기상관성 정보를 반영할 필요가 있다. 이 연구에서는 시계열 기온 분포도 제작을 위해 1개월 동안 1시간 간격으로 획득된 기온 관측소 자료를 대상으로 시공간 크리깅을 적용하였다. 우선 기온자료를 결정론적 경향 성분과 확률론적 잔차 성분으로 분해한 후에, 경향 성분 모델링 과정에 기온과 연관성이 높은 고도 자료를 부가 자료로 통합하여 지형 효과를 반영하는 경향 성분을 모델링하였다. 잔차 성분에 대한 시공간 베리오그램 모델링에는 곱-합 모델을 적용하여 시간과 공간 베리오그램의 상호 연관성을 반영하도록 하였다. 이러한 시공간 베리오그램 모델을 이용하여 시공간 정규 크리깅을 적용한 결과, 기존 공간적 자기상관성만을 고려하는 정규 크리깅과 고도 자료를 부가 자료로 이용하는 회귀분석 크리깅에 비해 상대적으로 높은 예측 능력을 보였다. 이러한 결과는 고도 자료와 더불어 시공간 자기상관성 정보의 이용이 중요함을 지시한다. 따라서 공간적으로 가용할 수 있는 자료의 수가 한계가 있지만 시계열적으로 자료 획득이 가능한 변수를 분석할 때, 시공간 크리깅이 유용한 내삽 방법론으로 적용될 수 있을 것으로 기대된다.

• 한국생산제조학회지
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• 제9권2호
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• pp.45-51
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• 2000

This study proposes that analysis and evaluation method of time series ultrasonic signal using the chaotic feature extrac-tion for degradation extent. Features extracted from time series data using the chaotic time series signal analyze quantitatively material degradation extent. For this purpose analysis objective in this study if fractal dimension lyapunov exponent and strange attractor on hyperspace. The lyapunov exponent is a measure of the rate at which nearby trajectories in phase space diverge. Chaotic trajectories have at least one positive lyapunov exponent. The fractal dimension appears as a metric space such as the phase space trajectory of a dynamical syste, In experiment fractal(correlation) dimensions and lyapunov experiments showed values of mean 3.837-4.211 and 0.054-0.078 in case of degradation material The proposed chaotic feature extraction in this study can enhances ultrasonic pattern recognition results from degrada-tion signals.

• The Journal of Korean Physical Therapy
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• 제14권4호
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• pp.45-54
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• 2002

The purpose of this study was to describe the gait pattern and parameters of the healthy elderly over 65years of age by the GATERite system. The subjects were sorted into two groups, depending on their sex: male and female. And female subjects were sorted into three groups, depending on their age. From time parameters and space parameters of gait cycle, between groups, the following results were made. The time parameters such as cadence, velocity, step time, single support and double support were the less the male than the female. And the higher age, the lower value except 80 age group, while no statistically significant. The space parameters(step length and stride length) were the longer the male than the female, and the higher age, the lower value while no statistically signigicant. The functional ambulation profile was high correlation with time and space parameters statistically significant.

• 한국실내디자인학회논문집
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• 제25권5호
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• pp.130-139
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• 2016

To determine "how humans move in space, what they want, and through which visual information they act and choose," this study aims to define in which sense space is preferred in gaze. The ultimate goal is to extract data of human visual awareness and preference in space. This study analyzed the observation characteristics perceived through observation frequency and time depending on the purpose cafe customers to understand what intension of visiting the space has on the observation characteristics which are the results obtained as information through visual perception. This research methods are as follows. First, the areas of preference in $caf{\acute{e}}$ space gazed by visual concentration are analyzed by divided into 12 by 12 grid A and B images separated depends on existence of people. Second, eye-tracking visual path in conscious gaze is analyzed to examine. Third, though the higher section frequency is likely to have more observation time, the interest area of I(3sec/180), II(6sec/360) and III(9sec/540) had higher frequency of Intention. The followings are the results of this study. First, the time range for searching or wandering and the observation characteristics could be estimated by the meaning of observation time by grade with the time-range out of the distribution of sections. Second, at the time distribution by section, when there was intention, the observation time was found to have higher occupation. In conclusion, this study is to determine the correlation of human concentration gazing at space images. It is an exploratory research on research methodologies, and aims to develop methodologies and provide basic data to plan attractive spaces in light of the subconscious of consumers in the future by interpreting gaze data related to concentration.

• Journal of Astronomy and Space Sciences
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• 제36권3호
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• pp.133-147
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• 2019

Challenging Minisatellite Payload (CHAMP) satellite magnetic data are used to investigate the latitudinal variation of the storm-time meso-scale field-aligned currents by defining a new metric called the FAC range. Three major geomagnetic storm events are considered. Alongside SymH, the possible contributions from solar wind dynamic pressure and interplanetary magnetic field (IMF) $B_Z$ are also investigated. The results show that the new metric predicts the latitudinal variation of FACs better than previous studies. As expected, the equatorward expansion and poleward retreat are observed during the storm main phase and recovery phase respectively. The equatorward shift is prominent on the northern duskside, at ${\sim}58^{\circ}$ coinciding with the minimum SymH and dayside at ${\sim}59^{\circ}$ compared to dawnside and nightside respectively. The latitudinal shift of FAC range is better correlated to IMF $B_Z$ in northern hemisphere dusk-dawn magnetic local time (MLT) sectors than in southern hemisphere. The FAC range latitudinal shifts responds better to dynamic pressure in the duskside northern hemisphere and dawnside southern hemisphere than in southern hemisphere dusk sector and northern hemisphere dawn sector respectively. FAC range exhibits a good correlation with dynamic pressure in the dayside (nightside) southern (northern) hemispheres depicting possible electrodynamic similarity at day-night MLT sectors in the opposite hemispheres.

• Journal of information and communication convergence engineering
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• 제3권3호
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• pp.119-121
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• 2005

This paper aims to estimate the delay time of multiple signals in a multi-path environment. It also seeks to carry out a comparative analysis with the existing delay time under the proposed algorithm to develop a new algorithm that applies the space average method in a MUSIC algorithm. Unlike the existing delay time estimation algorithm, the developed algorithm was able to estimate the delay time in 5ns low. Therefore, the algorithm proposed in this paper improved the existing delay time estimated algorithm.

• Journal of information and communication convergence engineering
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• 제15권1호
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• pp.21-27
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• 2017

In this research, we study the outage probability for distributed space-time coding-based cooperative (DSTC) systems with amplify-and-forward relaying over Rayleigh fading channels with a high temporal correlation where the direct link between the source and the destination is available. In particular, we derive the upper and lower bounds of the outage probability as well as their corresponding asymptotic expressions. In addition, using only the average channel powers for the source-to-relay and relay-to-destination links, we propose an efficient power allocation scheme between the source and the relay to minimize the asymptotic upper bound of the outage probability. Through a numerical investigation, we verify the analytical expressions as well as the effectiveness of the proposed efficient power allocation. The numerical results show that the lower and upper bounds tightly correspond to the exact outage probability, and the proposed efficient power allocation scheme provides an outage probability similar to that of the optimal power allocation scheme that minimizes the exact outage probability.