• 한국농공학회논문집
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• 제47권4호
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• pp.65-74
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• 2005

AnnAGNPS model was applied to a catchment mainly occupied with bushland for modeling non-point source pollution. Since the single event model cannot handle events longer than 24 hours duration, the event-based calibration was carried out using the continuous mode. As event flows affect sediment and nutrient generation and transport, the calibration of the model was performed in three steps: Hydrologic, Sediment and Nutrient calibrations. The results from hydrologic calibration for the catchment indicate a good prediction of the model with average ARE(Absolute Relative Error) of $24.6\%$ fur the runoff volume and $12\%$ for the peak flow. For the sediment calibration, the average ARE was $198.8\%$ indicating acceptable model performance for the sediment prediction. The predicted TN(Total Nitrogen) and TP(Total Phosphorus) were also found to be acceptable as the average ARE for TN and TP were $175.5\%\;and\;126.5\%$, respectively. The AnnAGNPS model was therefore approved to be appropriate to model non-point source pollution in bushland catchments. In general, the model was likely to result in underestimation for the larger events and overestimation fur the smaller events for the water quality predictions. It was also observed that the large errors in the hydrologic prediction also produced high errors in sediment and nutrient prediction. This was probably due to error propagation in which the error in the hydrologic prediction influenced the generation of error in the water quality prediction. Accurate hydrologic calibration should be hence obtained for a reliable water quality prediction.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4240-4258
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• 2016

A practical iterative channel estimation technique is proposed for the multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system in the high-speed mobile environment, such as high speed railway scenario. In the iterative algorithm, the Kalman filter and data detection are jointed to estimate the time-varying channel, where the detection error is considered as part of the noise in the Kalman recursion in each iteration to reduce the effect of the detection error propagation. Moreover, the employed Kalman filter is from the canonical state space model, which does not include the parameters of the autoregressive (AR) model, so the proposed method does not need to estimate the parameters of AR model, whose accuracy affects the convergence speed. Simulation results show that the proposed method is robust to the fast time-varying channel, and it can obtain more gains compared with the available methods.

• 제어로봇시스템학회논문지
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• 제4권2호
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• pp.203-208
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• 1998

This paper presents an adaptive fuzzy controller using an neural network and adaptation algorithm. Reference-model following neuro-fuzzy controller(RMFNFC) is invesgated in order to overcome the difficulty of rule selecting and defects of the membership function in the general fuzzy logic controller(FLC). RMFNFC is developed to tune various parameter of the fuzzy controller which is used for the discrete nonlinear system control. RMFNFC is trained with the identification information and control closed loop error. A closed loop error is used for design criteria of a fuzzy controller which characterizes and quantize the control performance required in the overall control system. A control system is trained up the controller with the variation of the system obtained from the identifier and closed loop error. Numerical examples are presented to control of the discrete nonlinear system. Simulation results show the effectiveness of the proposed controller.

• 한국통신학회논문지
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• 제38A권9호
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• pp.765-772
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• 2013

본 논문에서는 인천공항 Concourse 지역에서 항공정보통신 무선 채널의 경로 손실 모델에 관해 연구하였다. 항공정보통신 주파수 밴드인 VHF/UHF 채널 중에 두 개의 주파수에 대해 전파 측정을 수행하였다. 현재 운영 중인 송신 사이트에서 변조 신호를 제거한 캐리어 파워를 송신하였으며, 전파 측정을 위해 수신기를 장착한 이동 차량을 이용하여 Concourse 지역에서 전파 측정을 수행하였다. 송신 파워, 주파수, 안테나 위치 등은 현재 운용 조건과 같다. 경로 손실 계수 및 실험적인 경로 손실 식은 기본적인 경로 손실 모델 및 하타 모델 등을 이용하여 추출하였다. Concourse 지역에서 추출된 LOS/NLOS 경로 손실 계수는 128.2MHz 및 269.1MHz에서 각각 3.1/3.13 및 3.01/3.38이었고 예측 에러의 편차는 각각 2.77/3.17 및 4.01/3.66이었다. 추출된 경로 손실 계수를 이용하여 Concourse 지역에서 전파 경로 손실식과 실험적인 경로 손실 계수를 도출하였으며 또한 다른 전파 패스 모델과 비교하였다. 이러한 결과는 항공정보통신 사이트 최적 위치 선정 및 항공정보통신 서비스 평가에 도움이 될 것이다.

• Journal of Electrical Engineering and Technology
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• 제6권6호
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• pp.883-887
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• 2011

Location-based service (LBS) is becoming an important part of the information technology (IT) business. Localization is a core technology for LBS because LBS is based on the position of each device or user. In case of outdoor, GPS - which is used to determine the position of a moving user - is the dominant technology. As satellite signal cannot reach indoor, GPS cannot be used in indoor environment. Therefore, research and study about indoor localization technology, which has the same accuracy as an outdoor GPS, is needed for "seamless LBS". For indoor localization, we consider the IEEE802.11 WLAN environment. Generally, received signal strength indicator (RSSI) is used to obtain a specific position of the user under the WLAN environment. RSSI has a characteristic that is decreased over distance. To use RSSI at indoor localization, a mathematical model of RSSI, which reflects its characteristic, is used. However, this RSSI of the mathematical model is different from a real RSSI, which, in reality, has a sensitive parameter that is much affected by the propagation environment. This difference causes the occurrence of localization error. Thus, it is necessary to set a proper RSSI model in order to obtain an accurate localization result. We propose a method in which the parameters of the propagation environment are determined using only RSSI measurements obtained during localization.

• 한국멀티미디어학회논문지
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• 제7권11호
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• pp.1571-1579
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• 2004

비디오를 다양한 단말과 이종의 망에 효과적으로 제공하기 위한 방법 중에, FD(Frame Dropping)-CD(Coefficient Dropping) 트랜스코딩 기법은 계산량을 줄이고, 손쉽게 구현할 수 있다는 측면에서 주목을 받고 있다. 그러나, FD-CD트랜스코딩 기법은 CD에 의한 왜곡이 GOP내의 부호화 의존성을 갖는 프레임의 복호화 영상 품질에 많은 영향을 미친다. 본 논문에서는, CD로 인하여 각 프레임별로 전파되는 왜곡의 크기를 적응적으로 예측하는 모델링 기법을 제안한다. 제안된 기법은 각 프레임별로 부호화된 매크로블록의 부호화 모드 비율에 대해 적응적으로 구해진다. 모의실험을 통하여, 제안된 모델은 CD로 인해 초래되는 전체 왜곡크기를 잘 예측할 수 있음을 보이고, 또한, 부호화된 비트스트림에서 CD에 의해 초래되는 프레임 단위로 일정한 전체 왜곡을 삽입하는데 효과적임을 보인다.

• 한국해양학회지:바다
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• 제12권3호
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• pp.133-141
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• 2007

장파와 단파의 거동을 동시에 모의할 수 있는 확장형 Boussinesq 방정식에 대한 유한요소모형을 개발하였다. 3차 공간 미분항을 처리하기 위한 추가변수를 도입하고 Galerkin 가중잔차방법을 적용하여 모형을 수립하였으며, 시간적분방법으로 Adams-Bashforth-Moulton Predictor Corrector 기법을 적용하여 비물리적인 수치분산이나 수치소산 현상을 줄일 수 있도록 하였다. 이 개발된 모형을 검증하기 위해 고립파가 전파하는 문제에 적용을 하였다. 개발된 모형을 적용한 결과 이론해 또는 수리실험 결과에 매우 양호한 일치를 보였다.

• International Journal of Contents
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• 제14권4호
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• pp.57-64
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• 2018

Among many UNESCO world heritage sites in Korea, "Historic Village: Hahoe" is adjacent to Nakdong River and it is imperative to monitor the water level near the village in a bid to forecast floods and prevent disasters resulting from floods.. In this paper, we propose a recurrent neural network with multiple hidden layers to predict the water level near the village. For training purposes on the proposed model, we adopt the sixth-order error function to improve learning for rare events as well as to prevent overspecialization to abundant events. Multiple hidden layers with recurrent and crosstalk links are helpful in acquiring the time dynamics of the relationship between rainfalls and water levels. In addition, we chose hidden nodes with linear rectifier activation functions for training on multiple hidden layers. Through simulations, we verified that the proposed model precisely predicts the water level with high peaks during the rainy season and attains better performance than the conventional multi-layer perceptron.

• 제어로봇시스템학회논문지
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• 제21권7호
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• pp.684-690
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• 2015

This paper presents a modified residual-based EKF (Extended Kalman Filter) for performance improvement of indoor positioning using WiFi RSSI (Received Signal Strength Indicator) measurement. Radio signal strength in indoor environments may have irregular attenuation characteristics due to obstacles such as walls, furniture, etc. Therefore, the performance of the RSSI-based positioning with the conventional trilateration method or Kalman filter is insufficient to provide location-based accurate information services. In order to enhance the performance of indoor positioning, in this paper, error analysis of the distance calculated by using the WiFi RSSI measurement is performed based on the radio propagation model. Then, an IARM (Irregularly Attenuated RSSI Measurement) error is defined. Also, it shows that the IARM error is included in the residual of the positioning filter. The IARM error is always positive. So, it is presented that the IARM error can be estimated by taking the absolute value of the residual. Consequently, accurate positioning can be achieved based on the IEM (IARM Error Mitigated) EKF with the residual modified by using the estimated IARM error. The performance of the presented IEM EKF is verified experimentally.

• 물과 미래
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• 제27권4호
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• pp.95-104
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• 1994

사행특성을 가진 복합하도에서의 홍수파해석을 위하여 사행도 모형을 개발하였다. 사행도 모형을 지배 방정식, 질량보존 오차 및 홍수파 해석 등을 통하여 기존의 세가지 홍수터 모형과 비교하였다. 사행도 모형에 의한 오차는 1.5-1.8% 정도로 나타났으나 분리하도 모형의 경우에는 1.5, 2.0의 사행도에서 각각 9.1, 27.4%로 큰 오차가 발생하였다. 사행도 모형은 홍수터를 가진 사행하도에서의 홍수전달 특성해석을 위하여 적용되었다. 사행도 모형에 의한 수치실험 결과, 홍수터의 조도와 홍수터의 하폭이 증가할수록, 사행도가 감소할수록 감쇠비와 유하시간비는 증가하였다. 본 모형은 보합하도 단면을 가지며 사행하는 국내 하천에서의 부정류 해석에 적용성이 클 것으로 판단되었다.