• 한국컴퓨터정보학회논문지
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• 제14권2호
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• pp.111-118
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• 2009

GPS의 이상 현상에 대한 대비 및 독자 항법 시스템을 구축하기 위해 유럽의 갈릴레오, 일본의 QZSS 등 세계선진각국의 GPS에 독립적인 위성항법시스템을 구축하고 있으며 GPS의 백업 용도로 지상항법 시스템인 Loran의 현대화 작업 등이 진행되고 있다. 국내에서도 독자항법에 대한필요성이 거론되었고 국내는 해상 및 국내 전 지역을 커버할 수 있는 신호 영역을 가진 DGPS신호의 대체항법 및 시각동기 인프라로서의 활용성에 대해 언급된 바 있다. GPS 보정 정보를 방송하는 DGPS 신호는 중파 대역으로 지표를 따라 전파되는 특성이 있다. 지표를 따라 전파되는 지표파는 지형의 전도율과 고도에 의해 전파의 전달시 추가지연(ASF)이 발생하고 이 추가지연은 항법 및 시각동기에 오차를 유발하게 된다. 지상항법시스템인 Loran은 중파를 이용하여 항법을 하고 있으며 DGPS 신호를 이용해 측위를 하기 위해서는 국내에 거의 연구사례가 없었으므로 유사 특성을 가진 중파를 이용한 Loran의 검증된 지연모델을 분석하고 이를 DGPS신호에 적용하는 것이 효율적일 것이다. 이에 본 논문에서는 중파의 검증된 지연모델을 분석하고 이를 국내 기술로 구현하여 DGPS 신호의 측위 가능성을 제안하고자 한다.

• Journal of Astronomy and Space Sciences
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• 제9권1호
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• pp.69-88
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• 1992

전파 전파에 있어서 전리층의 영향은 산란, 감쇄, 각오차, 위치오차, 및 시간 지연등이다. 적당한 전리층 조건 아래서 하전입자는 전파로 부터 에너지르 뺏어 전파 감쇄의 원인이 되게 한다. 또한 전자밀도가 균일하지 않은 경로를 따라 전파가 전파되는 경우, 전파 방향, 위치, 전파 시간등에 변화가 생기게 된다. 본 논문에서는 1985년 1월 부터 1989년 10월까지 전파연구소에서 관측된 국내 전리층 관측자료를 토대로 Chapman법칙에 따른 전리층 모델을 정립 하였으며, 이로부터 전파 전파에 있어서 각 오차, 위치 오차, 시간 지연, 및 감쇄등을 주파수와 위성의 고도에 따라 고찰하여 보았다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.249-256
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• 2003

To investigate the safety and stability of the concrete lining, numerous studies have been conducted over the years and several methods have been developed. Most signal processing method of NDT techniques has based on the Fourier analysis. However, the application of Fourier analysis to analyze recorded signal shows results only in frequency domain, it is not enough to analyze transient waves precisely. In this study, a new NDT technique .using the wavelet theory was employed for the analysis of non-stationary wave propagation induced by mechanical impact in the concrete lining. The wavelet transform of transient signals provides a method for mapping the frequency spectrum as a function of time. To verify the availability of wavelet transform as a time- frequency analysis tool, model experiments have been conducted on the concrete lining model. From this study, it was found that the contour map by Wavelet transform provides more distinct results than the power spectrum by Fourier transform and it was concluded that Wavelet transform was an effective tool for the experimental analysis of dispersive waves in concrete structures.

• Journal of electromagnetic engineering and science
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• 제12권1호
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• pp.77-84
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• 2012

This paper introduces our development of a MIMO-OTA system with simplified configuration. The key element of our proposal is the adoption of an antenna branch-controlled configuration for generating multipath delayed waves. The signal processing is carried out on IF band signal with an FPGA in a fading-emulator-type MIMO-OTA measurement system. The proposed scheme is largely different from available system configurations for the fading simulator method of constructing the OTA test environment. We describe the principle of the proposed scheme, channel model incorporated in the system, basic configuration of the developed system, and its performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권1호
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• pp.87-107
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• 2015

Considering the localization estimation issue in mixed line-of-sight (LOS)/non-LOS(NLOS) environments based on received signal strength (RSS) measurements in wireless sensor networks, a grid-based correlation method based on the relationship between distance and RSS is proposed in this paper. The Maximum-Likelihood (ML) estimator is appended to further improve the localization accuracy. Furthermore, in order to reduce computation load and enhance performance, an improved recursively version with NLOS mitigation is also proposed. The most advantages of the proposed localization algorithm is that, it does not need any prior knowledge of the propagation model parameters and therefore does not need any offline calibration effort to calibrate the model parameters in harsh environments, which makes it more convenient for rapid implementation in practical applications. The simulation and experimental results evidence that the proposed localization algorithm exhibits good localization performance and flexibilities for different devices.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.309-314
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• 2003

Impact Echo method has been successful in detecting a variety of defects in concrete structure. This study has the objectives to show important aspects of applying the Discrete Wavelet Transform(DWT) to signal processing of Modified Impact Echo(ModIE) Measurement systems and to the understanding of the seismic wave propagation. The data of ModIE were processed by DWT and compared with the results of conventional ModIE Analysis. Although it is inconsistent in the evaluated thickness of concrete lining, the DWT provides the features of separation, synthesis and de-noising in the original signal. The application of technique by wavelet was explained numerically with ABAQUS and performed experimentally with a real scale model in this work. Further works on the possible ways for creating new mother wavelet are specially needed for the enhancement of seismic signal analysis.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송∙미디어공학회 2020년도 하계학술대회
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• pp.717-720
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• 2020

An indoor localization system that uses Wi-Fi RSSI signals for localization gives accurate user position results. The conventional Wi-Fi RSSI signal based localization system uses raw RSSI signals from access points (APs) to estimate the user position. However, the RSSI values of a particular location are usually not stable due to the signal propagation in the indoor environments. To reduce the RSSI signal fluctuations, shadow fading, multipath effects and the blockage of Wi-Fi RSSI signals, we propose a Wi-Fi localization system that utilizes the advantages of Wi-Fi RSSI heat maps. The proposed localization system uses a regression model with deep convolutional neural networks (DCNNs) and gives accurate user position results for indoor localization. The experiment results demonstrate the superior performance of the proposed localization system for indoor localization.

• Journal of information and communication convergence engineering
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• 제15권3호
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• pp.143-150
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• 2017

Absorption of microwave radio frequency signal by atmospheric rain is prevalent at frequencies above 10 GHz. This paper presents the studies on rain attenuation at 18 GHz for 3.2 km experimental link between Khumdang (Korea Telecom, KT station) and Icheon (National Radio Research Agency, RRA station). The received signal data for rain attenuation and rain rate were collected at 10 second intervals over a three year periods from 2013 to 2015. Out of several models, the paper present discussion and comparison of ITU-R P.530-16 model, Moupfouma model, Da Silva Mello model along with suitable rain attenuation prediction method. The limitation of research lies on the experimental system that is set up in only one location, however, the preliminary results indicate the application of suitable 1-minute rain attenuation model for specific site. The method provides useful information for microwave engineers and researchers in making decision over the choice of most suitable rain attenuation prediction in terrestrial links.

• 한국정보과학회논문지:정보통신
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• 제31권4호
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• pp.375-383
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• 2004

최근에 사용 편이성으로 인해 다양한 무선 이동 네트워크들이 널리 보급되면서, 무선 네트워크성능을 향상시키기 위한 연구가 활발히 진행되고 있다. 무선 네트워크에서의 패킷 손실은 유선 네트워크의 혼잡이 아닌, 전파 오류로 인해 빈번히 발생되기 때문에, 시뮬레이션에서 무선 네트워크의 성능을 정확히 평가하기 위해서는 알맞은 무선 채널 모델을 채택해야 한다. 적합한 채널 모델은 사용 주파수 영역, 신호출력, 방해물 존재 유무, 평가하는 프로토콜의 비트 오류에 대한 민감성 둥 여러 가지 변수를 고려하여 선택해야 한다. 본 논문에서는 센서(Sensor) 채널의 고 전파 오류 특성을 분석하고, 센서 채널에 알맞은 채널 모델을 결정한다. 또한 센서 네트워크에서 수집한 비트 오류 데이타와 다양한 이론적 무선 채널 모델링 방식을 이용하여 링크계층 FEC(Forward Error Correction) 알고리즘과 TCP 성능 변화를 평가한다. 10일간의 센서 채널 트레이스와의 비교 분석에 의하면, CM(Chaotic Map) 모델은 센서 채널의 BER 편차와 PER(Packet Error Rate) 같을 각각 3배와 10배 이내의 오차 범위에서, 다른 모델은 수십 배 이상 오차범위에서 예측한다. FEC 알고리즘과 세가지 TCP (Tahoe, Reno, 그리고 Vegas) 시뮬레이션 실험에서도 CM 모델은 트레이스와 유사한 성능 변화를, 다른 모델은 최대 10배 이상의 오차를 보인다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권6호
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• pp.989-996
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• 2008

Recently, a few types of fish-cage in open sea are researched. This fish-cage has to operate monitoring system for keeping an optimum living condition for fish. The most efficient monitoring system is WVMS(Wireless Vision Monitoring System) for fish-cage in open sea. WVMS should be able to transmit video signal and communicate with each controller. So. it needs to be based on WLAN(Wireless LAN) which has characteristic of higher transfer-rate, In this paper, we propose a structure of WVMS using WLAN equipments for maritime environment and prove its effectiveness. We present the propagation loss model of WVMS's communication channel. measured by field test, and discuss its validity compared with the predictive value based on the Friss propagation model and Plane earth reflection model. We present the number of frames that is received from WLAN modem connecting with underwater-camera in field test spots. As a result, we confirmed that proposed WVMS is suitable for maritime environment and it is possible to be applied to fish-cage in open sea on 'seogwipo'.