• 한국전자파학회논문지
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• 제21권9호
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• pp.995-1004
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• 2010

채널의 상태가 변하는 전송 환경에서 수신된 신호에 대한 잡음비를 추정하여, 보다 효율적으로 신호를 전송하는 것은 현대 통신 시스템에서 중요한 기술이다. 기존 NDA(Non-Data-Aided) SNR 추정 방법은 M진 APSK 또는 같은 고차원 신호의 SNR 추정 성능이 떨어진다. 본 논문에서는 OFDM 시스템에서 블록 단위 수신 신호의 영점 자기 상관과 decision feedback 신호의 자기 상관 및 상호 상관을 이용하는 SNR 추정 방법을 제안한다. 본 논문에서 제안한 방법은 decision feedback 신호의 2차 모멘트인 영점 자기 상관을 이용하여 SNR을 추정하는 Type 1 방식과 4차 모멘트 성질을 갖고 있는 영점 자기 상관과 상호 상관을 이용한 Type 2 방식이다. 이 두가지 SNR 추정 방식은 OFDM 시스템에서 블록 단위 수신을 할 때, 신호의 상관 관계에 기반을 두고 있어 SNR 추정 방법의 실용적인 구현이 가능하게 하고, decision feedback 신호를 사용함으로써 QAM 신호에서도 종전의 SNR 추정 방식들보다 비교적 안정적인 추정 성능을 보인다. 또한, decision feedback 신호를 사용할 때 자기 상관과 상호 상관의 오차에 따른 SNR 추정 식을 수식적으로 유도한다. 그리고 Monte Carlo 시뮬레이션을 통해 제안한 SNR 추정 방법의 성능을 확인한다.

• 대한의용생체공학회:의공학회지
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• 제17권3호
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• pp.347-354
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• 1996

This paper presents digital hearing aids signal processing system in WT(wavelet transform) domain. For implementation of hearing aids in WT domain, the gain in frequency domain is approximated in WT domain. We also present the gain selection algorithm to deal with the change of input signal power. Most transform methods produce blocking effect, and this effect degrades the convergence rate of feedback canceller. As a solution, we proposed wavelet transform bascd feedback canceller. To evaluate the performance, we compared it with LOT (lapped orthogonal transform) method in the frequency domain. This system has not shown the blocking effect, and improves convergence rate as compared with the LOT based feedback canceller.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.321-324
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• 1997

In this paper, Active Noise Control(ANC) algorithm is proposed based on the estimated frequency estimator of the reference signal. The conventional feedforward ANC algorithms should measure the reference and use it to calculate the gradient of the squared error and filter coefficients. For ANC systems applied to aircrafts and passenger ships, engines from which reference signal is usually measured is so far from seats where main part of controller is placed that the scheme might be difficult to implement or very costly. Feedback ANC algorithm which doesn't need to measure the reference uses the error signal to update the filter and is sensitive to unexpected transient noise like a sneeze, clapping of hands and so on The proposed algorithm estimates frequencies of the desired signal in real time using adaptive notch filter. New frequency estimation algorithm is proposed with the improved convergence rate, threshold SNR and computational simplicity. Reference is not measured but created with the estimated frequencies. It has strong similarity to the conventional feedback control because reference is made from error signal. Enhanced error signal is used to update the controller for better performance under the measurement noise and impact noise. The proposed ANC algorithm is compared with the conventional feedback control.

• 로봇학회논문지
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• 제5권1호
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• pp.48-54
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• 2010

Ankle-foot orthosis with a pneumatic rubber actuator, which is intended for the assistance and the enhancement of ankle muscular activities was developed. In this study, the effectiveness of the system was investigated during plantarflexion motion of ankle joint. To find a effectiveness of the system, the subjects performed maximal voluntary isokinetic plantarflexion contraction on a Biodex-dynamometer. Plantarfexion torque of the ankle joint is assisted by subject's soleus muscle that is generated when ankle joint do plantarflexion motion. We used the muscular stiffness signal of a soleus muscle for feedback control of ankle-foot orthosis as physiological signal. For measurement of this signal, we made the muscular stiffness force sensor. We compared a muscular stiffness force of a soleus muscle between with feedback control and without it and a maximal plantarflexion torque between not wearing a ankle-foot orthosis, without feedback control wearing it and with feedback control wearing it in each ten elderly adults. The experimental result showed that a muscular stiffness force of a soleus muscle with feedback control was reduced and plantarflexion torque of an ankle joint only wearing ankle-foot orthosis was reduced but a plantarflexion torque with feedback control was increased. The amount of a increasing with feedback control is more higher than the amount of a decreasing only wearing it. Therefore, we confirmed the effectiveness of the developed ankle-foot orthosis with feedback control.

• 반도체디스플레이기술학회지
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• 제14권2호
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• pp.9-16
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• 2015

In this paper, selection criterions on selection diversity are researched. The diversity is applied to the multiple antenna system based on wireless access in vehicular environment (WAVE) standard for rapid varying channel. Least squares (LS) based decision feedback equalizer (DFE) are used for channel equalization. Received signal is regenerated by means of the decision feedback path. In the selection diversity, the regenerated signal as well as the received signal is selected according to selection criterion. The decision feedback algorithm can follow the fast speed of WAVE fading channel. To control the tracking speed of the time-varying channel, simple low pass filter is used. Finally, the estimated channel value recovers the distorted payloads. Signal power before automatic gain control (AGC) in analog stage can be used as a selection criterion. In the digital stage, signal power after AGC, noise power after AGC, signal to noise ratio after AGC and cross-correlation method can be used as selection criterions. According to the simulation results, the performance of the selection diversity is improved in comparison with that of the combining diversity for the WAVE fading channel.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2006년도 하계학술대회
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• pp.57-61
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• 2006

As high speed internet users are tremendously increasing, three are keenly in need of development of high speed portable internet technology which can provide high quality wireless internet service cheaply even in the mobile. Unlike the FDD-CDMA, TDD-OFDMA has relatively poor wave environment with inducing interference, fading and delay because it agrees to multi-carrier modulation method and time-division radio telecommunication system. To solve this problem, it is necessary to develop repeater operating by digital signal processing method which have more strict wireless channel control and wave signal processing technology over TDD telecommunication equipments. This thesis is dealing with design and implementation of Digital RF Repeater which implemented 'Synchronization Acquisition Unit', 'TDD signal switching Unit', 'Feedback Signal Cancellation Unit'. Over this argument, we will develop digital RF repeater with more cheap, more adaptive in wave environment like oscillation control, adaptive wave monitoring and output increasing and having control function as a result it will be helpful for success in high speed portable internet service business.

• ETRI Journal
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• 제31권4호
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• pp.357-364
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• 2009

In this paper, we propose a novel equalization on-channel repeater (OCR) with a feedback interference canceller (FIC) to relay terrestrial digital multimedia broadcasting signals in single frequency networks. The proposed OCR not only has high output power by cancelling the feedback signals caused by insufficient antenna isolation through the FIC, but also shows better output signal quality than the conventional OCR by removing multipath signals existing between the main transmitter and the OCR through an equalizer. In addition, computer simulations and laboratory test results demonstrate that the proposed OCR successfully cancels feedback signals and compensates channel distortions and provides a higher quality transmitting signal with higher output power than conventional OCRs.

• 융합신호처리학회논문지
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• 제7권3호
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• pp.130-135
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• 2006

원형관의 닥트를 사용하여 1 차원 구동원으로써 라우드스피커와 환기용 팬을 사용하여 각종 알고리즘인 X-LMS 알고리즘과 Filtered-U 알고리즘 그리고 Full-Feedback Filtered-U 알고리즘으로 구성한 DSP 적응필터를 작동시켜 닥트에 적용할 수 있는 능동소음 제어시스템 실현의 가능성에 대하여 여러 가지 실험을 하였다. 1 차 구동원을 환기용 팬을 사용할 때 2 차 제어용 신호가 환기용 팬에 가까이 있는 탐지 마이크로폰에 혼입되는 현상을 고려한 Full-Feedback Filtered-U LMS 알고리즘을 능동제어 시스템에 적용하여 적응제어 필터를 작동하면 시스템이 발산되지 않고 안정상태에서 주파수 범위 170-250Hz 사이에서 다른 알고리즘에 비하여 소음량이 최대치에서 10dB 정도 감소되었다.

• Journal of Electrical Engineering and information Science
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• 제3권1호
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• pp.126-130
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• 1998

In this paper, a new interference rejection filter using the data-recycling technique is presented. The reference signal of the interference rejection filter is formed by using chip decisions, which is correlated with the narrowband interference components of the received signal. The decision feedback techniques reduce the distortion of the desired signal, which is introduced by the interference rejection filter through he use of feedback chip decisions. In order to update the filter coefficients a simple and efficient data-recycling technique that has improved performance over the conventional LMS algorithm is used. The performance of the proposed interference rejection filter is compared to filter with conventional LMS linear filter. The results show that the convergence speed of the proposed interference rejection filter using decision feedback and data-recycling technique is significantly faster than that of the conventional filters. Also, BER performance of the interference rejection filter demonstrates the superiority of the proposed filter algorithm.

• 한국광학회지
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• 제5권2호
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• pp.291-297
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• 1994

Erbium첨가 광섬유 증폭기에서 증폭된 자연방출광(ASE) 출력의 일부를 대역투과 파장 필터를 거쳐 입력단으로 루프 귀환시켜 광증폭기를 특정 파장에서 발진시킴으로써 신호광에 대한 증폭 이득을 일정치에 고정시켰다. 증폭 이득과 ASE 출력 스펙트럼은 광증폭기가 발진하는한 입력광 power나 펌프광 power의 변화에 대하여 무관하였으며 귀환 루프의 손실에만 의존하였다. 또한 광증폭기에 저속으로 변조된 대신호가 입사하는 경우에도 이득포화에 의한 파형 왜곡없이 증폭이 가능하였다.