• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.2
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• pp.261-266
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• 2017

This study describes the design and implementation of SHF band Upconverter Digital Satellite Communication. The SHF band Upconverter unit consists of PLDROand frequency converter. In frequency converter, microstripBPF and LPF designed through the pre EMsimulation are implemented to minimize the unwanted spurious in frequency converter. Through the pre-simulation analysis ofspace environment, the possibility of and minimized about the malfunction of equipment and we designed a reliable SHF band Upconverter through simulation for a TID according to the vibration generated during the launch and space radiation environment, and compared pre-simulation of main performance results to test results about main performances of SHF band Upconverter after production.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.3
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• pp.95-105
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• 2009

Spam call is one of the main security threat in VoIP services. In this paper, we have designed simulation model for performance evaluation of VoIP spam defense mechanism. The simulation model has functions for performance evaluation such as calls generation and input/output comparison. Four representative caller models have been developed for performance evaluation and each model has its own characteristics as statistical parameters. The target mechanism of performance evaluation is SPIT(Spam over Internet Telephony) level decision algorithm, and we have derived SPIT levels of caller models. The performance evaluation model is designed using the DEVS formalism and DEVSJAVA$^{TM}$ is exploited for development and execution of simulation models.

• Journal of Advanced Navigation Technology
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• v.27 no.5
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• pp.568-573
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• 2023

Range resolution is the ability to distinguish different targets placed in same angular direction but at different distances from the radar. Normally, Range resolution requirement is defined as the width of transmitting pulse. The width of transmitting pulse does not mean the ability to distinguish two different targets. Range resolution performance to detect and track targets separately depends on the signal processing and tracking algorithm not only the width of transmitting pulse. This paper analyzes the processing steps in algorithms to affect the range resolution performance and verifies the results by roof-lab ground test using beacon signal. As a result, to track targets with the same angular position separately, it is desirable to have larger range difference than plot-track association test gate.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.539-549
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• 2007

To establish effective and prompt measures for energy conservation in public wastewater treatment plants in Korea, energy consumption rates in 233 utilities in 9 provinces and 7 metropolitan cities are investigated and compared to the rest of the world. Mean load factor for wastewater treatment utilities is 74.9% and those for influent pumps and aeration blowers are 56.2% and 61.0%, respectively. Mean electrical energy usages as the key performance indicators are $0.243kWh/m^3$ for overall sewage treatments and 2.07 kWh per unit kg BOD removal. Digester gas as one of major byproducts in the process amounts to $382,000m^3/day$ nationwide. While major part of the digester gas is used for sludge heating, only 7.3% of the gas is utilized for electricity generation. Both efficiencies for BOD removal and digestion gas generation are considerably lower than those in USA and EU utilities due to low concentration of organic material in influent wastewater. Such low energy regeneration, in turn, results in significantly higher energy consumption in Korean plants, compared to that in USA and EU ones.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.301-301
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• 2018

본 연구에서는 위성 기반 토양수분 자료를 수문모형에 자료동화하여 격자 단위에서 수문기상인자를 산출하고 그 정확성을 평가하였다. 수문모형으로는 Variable Infiltration Capacity(VIC) model을 선정하여 국내 주요 8개 댐 유역에 구축하였으며, 입력자료는 2008년 이후 10년간 자료를 수집하였으며, 2008-2012년의 관측 유량 자료를 사용하여 모형을 보정하였다. 모형의 보정을 위해 Isolated-Speciation Particle Swarm Optimization(ISPSO) 기법을 적용하여 매개변수를 추정하였고, 2013-2017년의 관측유량 자료를 통하여 모형의 성능을 검증하였다. VIC 모형에 자료 동화한 토양수분 자료는 AMSR2 위성 토양 수분 자료와 지상관측 토양수분 자료를 합성한 자료를 사용하였으며, 인공위성자료와 지상 자료를 조건부합성기법으로 합성한 토양수분자료는 각 격자별 토양수분을 더 정확히 산정하여 자료동화시 모형의 모의 정확도가 향상되는 경향을 보였다. 본 연구결과는 지상관측자료를 통해 보정된 위성관측 토양수분자료를 자료동화하여 수문모형의 정확도를 향상시키고, 미계측 유역에 대한 향상된 수문기상인자 정보를 제공함으로써 다양한 수문분석의 기초자료로 활용될 수 있을 것으로 기대된다.

• Journal of the Korea Society of Computer and Information
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• v.20 no.3
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• pp.47-56
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• 2015

Automated detection of interesting web pages could be used in many different application domains. Determining a user's interesting web pages can be performed implicitly by observing the user's behavior. The task of distinguishing interesting web pages belongs to a classification problem, and we choose white box learning methods (fixed effect logit regression and support vector machine) to test empirically. The result indicated that (1) fixed effect logit regression, fixed effect SVMs with both polynomial and radial basis kernels showed higher performance than the linear kernel model, (2) a personalization is a critical issue for improving the performance of a model, (3) when asking a user explicit grading of web pages, the scale could be as simple as yes/no answer, (4) every second the duration in a web page increases, the ratio of the probability to be interesting increased 1.004 times, but the number of scrollbar clicks (p=0.56) and the number of mouse clicks (p=0.36) did not have statistically significant relations with the interest.

• Journal of the Korean Society for information Management
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• v.36 no.4
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• pp.83-105
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• 2019

This study aims to suggest an effective method for the automatic classification of keywords with similar patterns by calculating pattern similarity of temporal data. For this, large scale news on the Web were collected and time series data composed of 120 time segments were built. To make training data set for the performance test of the proposed model, 440 representative keywords were manually classified according to 8 types of trend. This study introduces a Dynamic Time Warping(DTW) method which have been commonly used in the field of time series analytics, and proposes an application model, MA-DTW based on a Moving Average(MA) method which gives a good explanation on a tendency of trend curve. As a result of the automatic classification by a k-Nearest Neighbor(kNN) algorithm, Euclidean Distance(ED) and DTW showed 48.2% and 66.6% of maximum micro-averaged F1 score respectively, whereas the proposed model represented 74.3% of the best micro-averaged F1 score. In all respect of the comprehensive experiments, the suggested model outperformed the methods of ED and DTW.

• The Korean Journal of Applied Statistics
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• v.37 no.2
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• pp.255-263
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• 2024

GDP represents the total market value of goods and services produced by all economic entities, including households, businesses, and governments in a country, during a specific time period. It is a representative economic indicator that helps identify the size of a country's economy and influences government policies, so various studies are being conducted on it. This paper presents a GDP growth rate forecasting model based on a dynamic factor model using key macroeconomic indicators of G20 countries. The extracted factors are combined with various regression analysis methodologies to compare results. Additionally, traditional time series forecasting methods such as the ARIMA model and forecasting using common components are also evaluated. Considering the significant volatility of indicators following the COVID-19 pandemic, the forecast period is divided into pre-COVID and post-COVID periods. The findings reveal that the dynamic factor model, incorporating ridge regression and lasso regression, demonstrates the best performance both before and after COVID.

• Journal of Applied Reliability
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• v.8 no.3
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• pp.145-154
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• 2008

인공위성은 지상 시스템과는 달리 극한 발사환경 및 우주환경에 노출되고, 운용 중 수리가 불가능하며, 임무 실패에 따른 위험비용이 매우 크기 때문에 고신뢰성, 고비용의 부품, 장비 및 시스템을 채택하여 개념설계단계에서부터 신뢰성을 관리한다. 신뢰성 관리의 주요 목적은 설계변경 및 개발 사이클의 반복을 최소화하고, 개발비용을 절감하며, 시스템의 신뢰성을 향상시키기 위한 것으로서, 대부분의 우주시스템 개발 프로젝트에서는 제품보증(Product Assurance) 활동의 일환으로 수행된다. 제품보증 업무는 크게 품질보증, 신뢰성 관리, EEE 부품관리, 재료 및 공정(Material & Process) 관리, 오염관리, 소프트웨어 품질보증 등으로 구분되지만, 포괄적인 의미의 신뢰성 관리 범주에 이를 모두 포함시키기도 한다. 인공 위성의 개발과정에서 기술성능지표 중 하나로서 중점 관리되고 있는 시스템 신뢰성 관리의 세부기법, 프로세스, 개선 필요사항 등에 대하여 살펴보고자 한다.

• Information and Communications Magazine
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• v.32 no.9
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• pp.24-30
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• 2015

새로운 서비스의 실현을 목표로 하는 차세대5G이동통신에 대한 비전, 요구사항 및 주요 요소 기술들에 대한 연구가 다양하게 진행 중이다. 지연 시간에 민감한 새로운 저지연 서비스의 지원을 위해 5G 이동통신 비전의 핵심 성능 지표 중 하나로 무선구간에서 1ms 이내의 사용자 데이터 전송이 제시되었다. 본고에서는 ITU-R WP 5D의 5G 이동통신 비전 권고 내용들과 권고 내용을 직접적인 반영하는 5G 관련 기술 개발 단계는 아니지만 3GPP 에서 현재 진행 중인 Release-13 표준화 활동 중에서 사용자 데이터 전송에 있어서 지연 감소를 목표로 논의되는 후보 기술들을 살펴보고 이를 바탕으로 3GPP에서의 관련 표준화 동향을 정리한다.