• 한국항행학회논문지
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• 제7권2호
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• pp.162-170
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• 2003

In this paper, we propose a robust controller for trajectory control of n-link robot manipulators using feature based on visual feedback. In order to reduce tracking error of the robot manipulator due to parametric uncertainties, integral action is included in the dynamic control part of the inner control loop. The desired trajectory for tracking is generated from feature extraction by the camera mounted on the end effector. The stability of the robust state feedback control system is shown by the Lyapunov method. Simulation and experimental results on a 5-link robot manipulator with two degree of freedom show that the proposed method has good tracking performance.

• Journal of Communications and Networks
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• 제8권4호
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• pp.391-400
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• 2006

With the on-going wireless access technologies, the Internet has become accessible anytime anywhere. In wireless networks, link errors significantly degrade the performance of the transmission control protocol (TCP). To cope with this issue, this paper improves the recently-proposed terrestrial REFWA (T-REFWA) scheme by adding a new error recovery mechanism to its original design. In the T-REFWA scheme, senders are acknowledged with appropriate sending rates at which an efficient and fair utilization of network resources can be achieved. As the feedback values are computed independently of link errors, senders can keep transmitting data at high rates even in case of link error occurrences. Using this feature, the proposed error recovery mechanism can achieve high throughput in environments with high bit error rates. The throughput is further improved by disabling the exponential back-off algorithm of TCP so that long idle times are avoided in case of link errors. We show through simulations that the proposed method improves TCP performance in high bit error rates. Compared with several TCP variants, the proposed error recovery scheme exhibits higher link utilization and guarantees system fairness for different bit error rates.

• Journal of Power Electronics
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• 제18권1호
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• pp.116-128
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• 2018

Conventionally, in order to reduce the ac components of the dc-link capacitors of the two-level Half-Bridge Voltage Source Inverter (HB-VSI), high dc-link capacitances are required. This necessitates the employment of short-lifetime and bulky electrolytic capacitors. In this paper, an analysis for the performance of low dc-link capacitances-based HB-VSI is presented to elucidate its ability to generate an enhanced fundamental output voltage magnitude without increasing the voltage rating of the involved switches. This feature is constrained by the load displacement factor. The introduced enhancement is due to the ac components of the capacitors' voltages. The presented approach can be employed for multi-phase systems through using multi single-phase HB-VSI(s). Mathematical analysis of the proposed approach is presented in this paper. To ensure a successful operation of the proposed approach, a closed loop current controller is examined. An expression for the critical dc-link capacitance, which is the lowest dc-link capacitance that can be employed for unipolar capacitors' voltages, is derived. Finally, simulation and experimental results are presented to validate the proposed claims.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권3호
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• pp.816-839
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• 2023

In a random vector functional link (RVFL) network, shortcomings such as local optimal stagnation and decreased convergence performance cause a reduction in the accuracy of illumination correction by only inputting the weights and biases of hidden neurons. In this study, we proposed an improved regularized random vector functional link (RRVFL) network algorithm with an optimized grey wolf optimizer (GWO). Herein, we first proposed the moth-flame optimization (MFO) algorithm to provide a set of excellent initial populations to improve the convergence rate of GWO. Thereafter, the MFO-GWO algorithm simultaneously optimized the input feature, input weight, hidden node and bias of RRVFL, thereby avoiding local optimal stagnation. Finally, the MFO-GWO-RRVFL algorithm was applied to ameliorate the performance of illumination correction of various test images. The experimental results revealed that the MFO-GWO-RRVFL algorithm was stable, compatible, and exhibited a fast convergence rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권5호
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• pp.1778-1797
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• 2021

Document image binarization is an important pre-processing step in document analysis and archiving. The state-of-the-art models for document image binarization are variants of encoder-decoder architectures, such as FCN (fully convolutional network) and U-Net. Despite their success, they still suffer from three limitations: (1) reduced feature map resolution due to consecutive strided pooling or convolutions, (2) multiple scales of target objects, and (3) reduced localization accuracy due to the built-in invariance of deep convolutional neural networks (DCNNs). To overcome these three challenges, we propose an improved semantic segmentation model, referred to as DP-LinkNet, which adopts the D-LinkNet architecture as its backbone, with the proposed hybrid dilated convolution (HDC) and spatial pyramid pooling (SPP) modules between the encoder and the decoder. Extensive experiments are conducted on recent document image binarization competition (DIBCO) and handwritten document image binarization competition (H-DIBCO) benchmark datasets. Results show that our proposed DP-LinkNet outperforms other state-of-the-art techniques by a large margin. Our implementation and the pre-trained models are available at https://github.com/beargolden/DP-LinkNet.

• ETRI Journal
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• 제33권2호
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• pp.210-218
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• 2011

Battiti's mutual information feature selector (MIFS) and its variant algorithms are used for many classification applications. Since they ignore feature synergy, MIFS and its variants may cause a big bias when features are combined to cooperate together. Besides, MIFS and its variants estimate feature redundancy regardless of the corresponding classification task. In this paper, we propose an automated greedy feature selection algorithm called conditional mutual information-based feature selection (CMIFS). Based on the link between interaction information and conditional mutual information, CMIFS takes account of both redundancy and synergy interactions of features and identifies discriminative features. In addition, CMIFS combines feature redundancy evaluation with classification tasks. It can decrease the probability of mistaking important features as redundant features in searching process. The experimental results show that CMIFS can achieve higher best-classification-accuracy than MIFS and its variants, with the same or less (nearly 50%) number of features.

• 한국문헌정보학회지
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• 제39권1호
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• pp.45-58
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• 2005

이 연구는 한글 웹 문서를 클러스터링 하기 위한 자질 선정 방법에 대한 비교연구이다. 이 연구에는 두 개의 코퍼스가 사용되었다. 클러스터링을 위한 실험 문서는 Naver의 자연과학 범주에서, 자질 선정을 위한 학습문서는 Yahoo Korea의 같은 범주에서 수집하였다. 우선 실험 문서를 단어자질과 동시링크, 그리고 이 둘을 혼합한 방법으로 클러스터링 한 다음 그 성능을 비교하였다. 다음으로 학습문서에서 카이제곱 통계량$(X^2)$, 정보획득량(IG), 그리고 상호정보량(MI)을 이용하여 용어자질을 선정한 다음. 이를 실험문서에 적용하여 클러스터링 성능을 비교하였다. 석기에 각 범주별로 최댓값을 갖는 용어들만을 해당 범주를 대표하는 자질로 선정하는 '최댓간 자질 선정기법'을 실험적으로 도입하여 적용해 보았다. 실험 결과 사용된 자질에 따른 한글 웹 문서 클러스터링 정확률은 자연어 $ 72.3\%$, 동시링크 $74.3\%$, 단어-링크 혼합 $74.8\%$, $X^2\;79.6\%\;Max\;X^2\;83.8\%$로 나타났다. 전통적 자질 선정 기법 중에서는 $X^2$가 약간 나은 성능을 보여 주었지만 큰 차이는 발견되지 않았다. 그러나 최댓값 자질 선정기법을 적용하였을 때 클러스터링 성능은 크게 향상되었다. 이 논문에서 제안된 최댓간 자질 선정 기법은 웹 문서의 자질 공간 축소와 한글 웹 문서의 클러스터링을 위한 간단하면서도 효과적인 수단이다.

• 정보통신설비학회논문지
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• 제4권1호
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• pp.7-13
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• 2005

In this paper, we propose the time synchronization module on fiber optic repeater to use optic line delay for obtaining time synchronization between up-link and down-link, in the 2.3 GHz WiBro network using TDD/OFDM (Time Division Duplex/Orthogonal Frequency Division Multiplexing) Generally, when we use fiber optic repeater to remove the shade area, it occurs transmission delay which is caused by optic transmission between RAS (Radio Access Station) and fiber optic repeater and inner delay of fiber optic repeater. Because the WiBro system is adopting a TOO method and there exists the difference of switching time which is caused by these delay between up-link and down-link, it occurs ISI (Inter Symbol Interference), ICI (Inter Carrier Interference). These interference results in the reduction of the coverage. And the inconsistency between Up-Link and Down-Link switching time maybe gives rise to the interruption of communication. In order to prevent these cases, we propose synchronization module using analog optic line delay as the one of synchronizing up-link and down-link. And we propose the consideration factor for the designing time synchronization module and the feature of optic line of analog method. The measurement result of optic line time synchronization module of structure proposed is as follows, the delay error of $0.5{\mu}g$ and the insertion loss value below maximum 4.5dB in range of $0{\sim}40{\mu}s$. These results fully meet the specification of WiBro System.

• 한국전자거래학회지
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• 제8권2호
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• pp.23-31
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• 2003

링크 기반 검색엔진은사용자의 질의어와 관련된 웹 문서들의 링크 정보를 이용하여 순위를 생성한다. 이러한 링크기반 웹 문서의 특성을 이용한 대표적인 순위 평가 알고리즘. HITS는 웹 페이지들 간의 상호 연결된 링크 정보로부터 웹 문서들의 중요도를 평가하고, 순위 정보에 따른 결과를 제시한다. 이러한 HITS 알고리즘의 문제점은 문서 내의 링크 빈도 수만을 고려하고, 입력 값으로 주어지는 웹 문서 집합의 특성에 의존적이라는 것이다. 본 논문에서는 링크기반 웹 검색 엔진들로부터 얻어진 문서 집합에 대해 질의와 검색결과 간의 적합도를 향상시킨 HITS 알고리즘을 수행하는 검색 에이전트를 설계하였다. 이로써 향상된 검객 성능과 결과의 지역성을 보완한다.

• Journal of Power Electronics
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• 제19권6호
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• pp.1351-1365
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• 2019

This paper proposes two modified Z-source inverter topologies, namely an embedded L-Z-source inverter (EL-ZSI) and a coupled inductor L-Z source inverter (CL-ZSI). The proposed topologies offer a high voltage gain with a reduced passive component count and reduction in source current ripple when compared to conventional ZSI topologies. Additionally, they prevent overshoot in the dc-link voltage by suppressing heavy inrush currents. This feature reduces the transition time to reach the peak value of the dc-link voltage, and reduces the risk of component failure and overrating due to the inrush current. EL-ZSI and CL-ZSI possess all of the inherent advantages of the conventional L-ZSI topology while eliminating its drawbacks. To verify the effectiveness of the proposed topologies, MATLAB/Simulink models and scaled down laboratory prototypes were constructed. Experiments were performed at a low shoot through duty ratio of 0.1 and a modulation index as high as 0.9 to obtain a peak dc-link voltage of 53 V. This paper demonstrates the superiority of the proposed topologies over conventional ZSI topologies through a detailed comparative analysis. Moreover, experimental results verify that the proposed topologies would be advantageous for renewable energy source applications since they provide voltage gain enhancement, inrush current, dc-link voltage overshoot suppression and a reduction of the peak to peak source current ripple.