• 대한수학회보
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• 제47권1호
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• pp.39-51
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• 2010

In this paper we consider the uniform central limit theorem for a martingale-difference array of a function-indexed stochastic process under the uniformly integrable entropy condition. We prove a maximal inequality for martingale-difference arrays of process indexed by a class of measurable functions by a method as Ziegler [19] did for triangular arrays of row wise independent process. The main tools are the Freedman inequality for the martingale-difference and a sub-Gaussian inequality based on the restricted chaining. The results of present paper generalizes those of Ziegler [19] and other results of independent problems. The results also generalizes those of Bae and Choi [3] to martingale-difference array of a function-indexed stochastic process. Finally, an application to classes of functions changing with n is given.

• Current Optics and Photonics
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• 제6권3호
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• pp.332-336
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• 2022

Given a cubic space, it is easy to uniformly illuminate the floor with light sources placed on top. However, little has been reported about uniform illumination on walls with the same configuration of light sources. Here we present a luminaire consisting of nine light-emitting diodes (LEDs) with perfect Lambertian distribution, placed on the top as a 3 × 3 rectangular LED array. The distances between LEDs and tilt angles of each individual LED are adjustable and optimized by an annealing algorithm. After optimization, the array produces a rectangular illumination pattern on one wall with a uniformity of about 89%. Analysis shows that the tilt angles of individual LEDs are key parameters for uniform side illumination. In a scenario that is more practical, the tilt angles of all the LEDs are set to be the same, only decreasing the uniformity to 83%.

• Journal of Power Electronics
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• 제16권2호
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• pp.631-642
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• 2016

Usually, the output characteristics of a photovoltaic (PV) array are significantly affected by non-uniform irradiance which is caused by ambient obstacles, clouds, orientations, tilts, etc. Some local maximum power points (LMPP) in the current-voltage (I-V) curves of a PV array can result in power losses of the array. However, the output power at the global maximum power point (GMPP) is different in different interconnection schemes in a PV array. Therefore, based on the theoretical analysis and mathematical derivation of different topological structures of a PV array, this paper investigated the output characteristics of dual series PV arrays with different interconnections. The proposed mathematical models were also validated by experimental results. Finally, this paper also concluded that in terms of performance, the total cross tied (TCT) interconnection was not always the optimal structure, especially in a dual series PV array. When one of the PV modules was severely mismatched, the TCT worked worse than the series parallel (SP) structure. This research can provide guidance for switching the interconnection to gain the greatest energy yield in a changeable- structure PV system.

• 한국음향학회지
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• 제39권3호
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• pp.191-199
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• 2020

현재 압축센싱 기반 도래각 추정 알고리듬의 연구는 활발히 진행 중이나 비균일 센서 배열 기반 공분산 fitting 알고리듬의 성능에 대한 연구는 진행되지 않았다. 본 논문에서는 주파수 영역으로 확장된 압축센싱 기반 공분산 fitting 알고리듬의 유도과정을 다루며 센서배열이 비균일하게 배치된 경우와 센서배열의 일부 소자에 고장이 발생한 경우에 대한 해당 알고리듬의 도래각 추정 성능을 비교하였다.

• 한국전자파학회논문지
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• 제13권3호
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• pp.279-287
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• 2002

본 논문에서는 광대역에서 광각을 조양할 수 있는 대칭형 구조의 선형 우상배열 송신기용 초고주파 렌즈를 설계하였다. 선형 위상 배열 송신기의 정확한 빔 조향 특성을 얻기 위해 렌즈의 균일한 진폭 전달 특성을 얻는데 중점을 두었다. 빔 포트 8개, 배열 포트 8개로 구성된 초고주파렌즈의 입.출력 포트간 삽입손실의 편차는 $\pm$3.1㏈로써 6~18㎓ 대역에 대해 매우 균일한 특성을 얻었다. 8개로 선형 배열된 안테나를 이용해 방위각 $\pm$60$^{\circ}$의 조향 특성을 얻을 수 있음을 확인하였으며, 측정한 렌즈 특성과 다중빔 조향 패턴을 제시하였다.

• 한국군사과학기술학회지
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• 제12권1호
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• pp.97-105
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• 2009

In this paper, the performance of AP(Alternating Projection) and EM(Expectation Maximization) algorithms is investigated in terms of detection of multiple signals, resolvability of coherent signals and the efficiency of sensor array processing. The basic idea of these algorithms is utilization of relaxation technique of successive 1D maximization to solve a direction finding problem by maximizing the multidimensional likelihood function. It means that the function is maximized over only for a single parameter while the other parameters are fixed at each step of the iteration. According to simulation results, the algorithms showed good performance for both incoherent and coherent multiple signals. Moreover, some advantages are identified for direction finding with very small samples and fast convergence. The performance of AP algorithm is compared with that of EM using multiple criteria such as the number of sensor, SNR, the number of samples, and convergence speed over uniform circular array. It is resulted AP algorithm is superior to EM overally except for one criterion, convergence speed. Especially, for EM algorithm there is no performance difference between incoherent and coherent case. In conclusion, AP and EM are viable and practical alternatives, which can be applied to a direction under due to the resolvability of multi-path signals, reliable performance and no troublesome eigen-decomposition of the sample-covariance matrix.

• 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.

• 한국통신학회논문지
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• 제22권7호
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• pp.1534-1542
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• 1997

In this paper, we present a performance improvement method for the direction-of-arrival (DOA) estimation algorithm of the narrowband signals incident on a uniform circular array. It is very important to estimate the covariance matrix effectively because the performance of DOA algorithm mainly depends on the exactness of the sampel coveriance matrix which is computed from the received samples of signals. In case of uniform circular array with the even number sensors, the structure of the arrray has a useful geometrical property. Therefore we present the method which can estimate covariance matrix more effectively using this property. The simulation results are shown to demonstrate the superior perfodrmance obtained by the proposed covariance matrix estimation method relative to that of the conventional estimation method.

• 한국통신학회논문지
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• 제42권4호
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• pp.723-730
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• 2017

본 논문에서는 안테나 간의 상호 결합을 고려한 온라인 보상 알고리즘을 고려하였으며, 이를 적용하기 위한 새로운 GPS(Global Positioning System)용 안테나 배열을 제안하였다. 제안한 안테나 배열 및 ULA(Uniform Linear Array), URA(Uniform Rectangular Array)에 대한 항재밍 성능 평가를 위해 복수의 재밍신호 환경에 대한 방향탐지를 환경 조건 별로 나누어서 진행하였다. 1. 상호 결합이 존재하지 않는 환경. 2. 상호 결합이 있으나 보상이 이루어지지 않는 환경. 3. 상호 결합 보상이 이루어진 환경. RMSE(Root Mean Square Error) 분석을 통해 온라인 보상 알고리즘이 작동함을 확인하고 복수의 재밍신호에서도 피크 검출이 가능함을 보였다.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2000년도 종합학술발표회 논문집 Vol.10 No.1
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• pp.369-373
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• 2000

This paper describes a design for microstrip EMC cross dipole array antenna with circular polarization. To realize the wide bandwidth and circular polarization, the electromagnetic-coupled cross dipole is used. To obtain the uniform aperture illumination, offset technique for array is adopted. In 20-element array design, the calculated axial ratio and gain are about 0.1 dB and 9.9 dBi at 12GHz, respectively. The frequency characteristics of a fabricated 20-element array antenna are measured. The calculated results agree well with the measured ones.