• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.11
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• pp.1022-1032
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• 2012

In OFDMA-based wireless mesh networks, synchronization of carrier frequencies among adjacent nodes is known to be difficult. In this paper, a distributed synchronization technique is proposed to solve the synchronization problem in OFDMA-based wireless mesh networks by using the bio-inspired algorithm. In the proposed approach, carrier frequencies of all nodes in a mesh network are converged into one frequency by locally synchronizing the frequencies of adjacent nodes. It may take a long time to be converged in some topologies since the convergence characteristic of carrier frequencies in a mesh network may vary depending on the size of the network and deployment of nodes. It is shown that fast frequency synchronization, not heavily depending on the topology, can be achieved through the proposed algorithm with an adjustable weight.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.8 s.338
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• pp.25-32
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• 2005

Frequency hopping system has been adopted to many communication systems in order to overcome the inferior situation such as jamming environment. But typically its processing gain being limited, data interfered by jamming signal could not be fully recovered. This can be enhanced by combing FH system with spatial interference canceller which is a kind of active beamformer In this Paper, we proposed the compensation method of weight vector discrepancy according to the hopped frequencies and the PMBF method which is able to eliminate the inference effectively with less computational complexity. That is, the steering vector of wanted signals can be calculated from the frame without jamming signals using eigen analysis. New projection matrix extracted by the steering vector of wanted signal eliminates the interferences from the covariance matrix of received signal including wanted signal and jamming signals. This PMBF has similar performance of SINR beamformer with less computational complexity.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.203-213
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• 2023

In medical ultrasound imaging systems, Side lobes may appear if signals outside the imaging point are not completely removed during receive focusing. If the time signal of the side lobe overlaps with the time signal (main lobe) from the image point, it is difficult to completely remove it using filter processing in the time domain. However, In the receive focusing process, when time-channel signals are Fourier-transformed, the main lobe and side lobe signals are spatially separated in the spectral domain. Therefore, the side lobes can be suppressed by multiplying the image with magnitude weights, which are determined by the magnitudes of the main and side lobes calculated in the spectral domain. In addition, when the main lobe and the side lobe spectrum are adjacent, the distance weight was applied based on the distance between them. In a 5 MHz ultrasound imaging system using a 64-channel linear transducer, point reflector and speckle images with cysts of various brightness were synthesized and weights were applied to the ultrasound image. Using computer simulations, we confirmed that the side lobes were greatly reduced without affecting the spatial resolution in the point reflector image, and the contrast was significantly improved in the cyst image with computer simulations.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10b
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• pp.592-594
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• 2003

이 논문에서는 wavelet과 sobel filter를 사용하여 영상의 객관적인 평가 점수를 계산하는 새로운 기법을 제안한다. 이 기법은 orthogonal wavelet 변환을 기초로 하고 있으며 원본 영상과 처리된 영상 데이터가 모두 가용하다는 것을 전제로 한다. Wavelet을 이용해 주파수에 따라 분할된 영상 정보를 이용해 각각의 부영역 별 차영상을 획득하고 이 획득된 영상의 에너지를 이용해 화질 평가 수치를 계산한다. 부영역 별로 획득된 영상은 일정한 크기의 블록으로 분할되어 동일한 블록 내에서 가용한 영상의 특징에 관한 정보(contrast, edge 영역의 분포 정도) 벡터와 내적하여 새로운 특징 벡터로 사용되고, 이 특징 벡터의 가중치를 최적화하여 높은 상관도의 화질평가 점수를 산출하게 된다.

• Annual Conference of KIPS
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• 2001.10b
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• pp.871-874
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• 2001

본 논문에서는 저작권 보호를 위한 다양한 디지털 워터마킹 기술들에 대한 연구들은 많이 발표되고는 있지만 원영상과 워터마크의 양에 대한 실질적인 상관관계를 고려한 연구는 미비한 것이 현실이다. 이에 본 논문에서는 주파수영역에서의 방법 중 DWT를 이용한 영상에 대하여 다양한 가중치와 임계값을 적용하여 워터마크의 특성인 비가시성, 무감지성 등을 만족하는 가장 적정한 워터마크 삽입 양을 도출하여 반복적인 실험의 결과로 나타난 RMSE와 PSNR의 분포를 측정하고 비교 분석하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.3
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• pp.443-449
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• 2001

This paper is simulation research to improve speech recognition rates under the noisy environment. We examines recognition ratio based on frequency-weighted HMM together with spectral subtraction. As results, frequency-weighted HMM with scaling coefficients is trained as a minimum error classification criterion, and is presents a higher recognition rates in noisy condition than a conventional method. Furthermore, spectral subtraction method gives 11 to 28% improvements for this frequency-weighted HMM in low SNR, and gives recognition rates of 81.7% at 6dB SNR of noisy speech.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.3
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• pp.459-464
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• 2001

We propose a transmit beamforming algerian for array antenna in FDD (Frequency Division Duplex) environments. The proposed method estimates the directions and spectra of the users, and constructs the spatial covariance matrix of the interferences at the downlink frequency. The weights are computed by that covariance matrix and desired user's direction vector Simulations are performed under Rayleigh fading environments. The proposed method don't need the data feedback, has the enhanced performance in BER (Bit Error Rate).

• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.766-768
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• 1999

인간시각체계의 특성을 이용하여 시각적으로 좋은 화질을 얻으면서도 효율적인 저 전송률의 웨이블릿 영상부호화를 실현하였다. MTF 함수를 이용하여 공간주파수 영역에서의 주파수 변화에 따른 콘트라스트의 민감도의 변화를 보상하였고, 공간 방향성에 대응하는 변수들을 추정하기 위하여 공간이방특성을 갖는 필터를 설계하였다. 이에 의하여 인간시각체계와 유사한 구조인 웨이블릿 변환영역에 적용할 수 있는 가중치를 도출하는 알고리즘을 개발하여 웨이블릿 변환 부호화에 적응하였다.

• Journal of Advanced Navigation Technology
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• v.9 no.2
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• pp.170-176
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• 2005

In this paper, we proposed watermarking algorithm based on wavelet transform. Discrete wavelet transform is involved to calculate additive energy strength. Considering imperceptibility, after computing contrast and texture sensitivity in gray-level image, we inserted watermark with variable weight due to the feature of coefficient block. Consequently, applying human visual system, the experimental results showed that the proposed algorithm satisfied the properties of robustness and imperceptibility that are the major conditions of watermarking.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10c
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• pp.553-555
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• 1998

효율적인 비디오 검색과 브라우징을 위해서는 비디오를 장면 단위로 나누는 비디오 분할과 더불어 분할된 비디오 셧을 대표하는 프레임을 군집화하는 기술이 필요하다. 이는 내용 기반 비디오 검색 및 브라우징의 바탕이 되는 핵심 기술로써, 국내외적으로 많은 연구가 요구되고 있는 실정이다. 본 논문에서는 주파수 정보를 이용한 대표 프레임 군집화 방법을 제안하고 실험 비디오 데이터에 대하여 그 성능을 평가해 본다. 제안된 방법에서는 웨이블렛 변환을 통하여 대표 프레임의 주파수 정보를 구한 후, 고주파 영역과 저주파 영역에 가중치를 두어 대표 프레임을 군집화 하였다. 제안된 방법을 드라마 비디오 데이터에 대하여 실험한 결과 군집화의 정확도가 우수할 뿐 아니라 군집화 정도를 조절할 수 있어 다양한 수준의 군집화를 수행할 수 있음을 확인할 수 있었다.