• 한국통신학회논문지
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• 제38B권1호
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• pp.54-62
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• 2013

본 논문에서는, 운영체제를 선택할 수 있고, 파워제어가 가능하며, 루트권한으로 사용할 수 있는 시스템으로 구성된, 원격지에서 사용할 수 있는 실험환경을 제안하고자 한다. 고대역 네트워크를 기반으로 하는 국제간 실험 환경을 제공하는 것을 목적으로 한다. 이렇게 하기 위해서, 성능적으로는, 백본 네트워크에 직접 연동되어 고대역의 전송 성능이 가능하여야 하고, 사용자 측면으로는, 운영체제 및 실험 어플리케이션들의 자유로운 설정이 가능하여야 하며, 또한 공유 시스템 환경에서, 사용자의 시스템 환경을 연속적으로 지속할 수 있어야 한다. 실험환경에 대한 사용자 편의성과 시스템을 구성하는 시간에 걸리는 반응성을 관점으로, 제안하는 실험환경이 사용자들에게 얼마나 유용한지 보여주고자 한다. 제안하는 방안은, 국제간 과학기술 협업 실험의 연구들을 하는 많은 연구자들에게 새로운 실험 환경을 제공하게 될 것이다.

• 대한의용생체공학회:의공학회지
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• 제17권4호
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• pp.449-458
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• 1996

Most of the conventional electrocardiowaphs foil to detect signals other than P-QRS-T due to the limited SNR and bandwidth. High-resolution electrocardiography(HRECG) provides better SNR and wider bandwidth for the detection of micro-potentials with higher frequency components such as vontricular late potentials(LP). We have developed a HRECG using uncorrected XYZ lead for the detection of LPs. The overall gain of the amplifier is 4000 and the bandwidth is 0.5-300Hz without using 60Hz notch filter. Three 16-bit A/D converters sample X, Y, and Z signals simultaneously with a sampling frequency of 2000Hz. Sampled data are transmitted to a PC via a DMA-controlled, optically-coupled serial communication channel. In order to further reduce the noise, we implemented a signal averaging algorithm that averaged many instances of aligned beats. The beat alignment was carried out through the use of a template matching technique that finds a location maximizing cross-correlation with a given beat tem- plate. Beat alignment error was reduced to $\pm$0.25ms. FIR high-pass filter with cut-off frequency of 40Hz was applied to remove the low frequency components of the averaged X, Y, and Z signals. QRS onset and end point were determined from the vector magnitude of the sigrlaIL and some parameters needed to detect the existence of LP were estimated. The entire system was designed for the easy application of the future research topics including the optimal lead system, filter design, new parameter extraction, etc. In the developed HRECG, without signal averaging, the noise level was less than 5$\mu$V$_rms RTI$. With signal averaging of at least 100 beats, the noise level was reduced to 0.5$\mu$V$_rms RTI$, which is low enough to detect LPs. The developed HRECG will provide a new advanced functionality to interpretive ECG analyzers.

• 센서학회지
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• 제31권6호
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• pp.423-427
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• 2022

A pressure sensor that mimics the sensing ability of human skin has emerged as high-profile technology because it shows remarkable applications in numerous fields such as robotics, human health monitoring, and artificial prosthetics. Whereas recent pressure sensors have achieved high sensitivity similar to that of human skin, they still show limited detection bandwidth. Moreover, once these e-skin are fabricated, their sensitivity and stiffness are fixed; therefore, they can be used for only limited applications. Our study proposes a new adaptive pressure sensor built with uniform gallium microdroplet-elastomer composite. Based on the phase transition of gallium microdroplets, the proposed sensor undergoes mode transformation, enabling it to have a higher sensitivity and wider detection bandwidth compared with those of human skin. In addition, we succeeded in extending a single adaptive pressure sensor to sensor arrays based on its high uniformity, reproducibility, and large-scale manufacturability. Finally, we designed an adaptive e-skin with the sensor array and demonstrated its applications on health monitoring tasks including blood pulse and body weight measurements.

• 한국정보통신학회논문지
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• 제14권3호
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• pp.603-612
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• 2010

최근 컴퓨팅 기술과 네트워크 기술의 발전으로 초고속 인터넷이 널리 보급되고 있지만 높은 대역폭을 필요로 하는 어플리케이션들의 점유율도 높아지면서 트래픽 혼잡으로 인한 네트워크 장애 발생율도 증가하고 있다. 데이터 전송에 시간적 제한을 갖는 어플리케이션인 VoD 시스템에서 네트워크 장애 발생 빈도가 증가하면 스트리밍의 지터로 인한 QoS의 저하를 초래할 수 있다. 기존의 인터넷 기반 스트리밍에 관한 연구들에서는 네트워크의 변화에 따라 적응적으로 QoS(Quality of Service)를 조절하는 기법들을 제시하여 왔다. 하지만 이는 서비스 제공자 입장에서의 문제 해결이며 네트워크상태에 상관없이 일정한 QoS를 원하는 사용자에게는 적합하지 않다. 본 논문에서는 네트워크 장애에 대비하여 선행하는 미디어 프레임을 탐욕적으로 전송함으로써 일정한 QoS를 보장하고자 하는 GPFT(Greedy Precedent Frame Transmission)기법을 제안한다. 제안하는 GPFT기법은 네트워크의 가용한 대역폭이 높을 경우 정상적인 프레임 재생율보다 빠르게 선행하는 프레임을 전송시켜 미리 클라이언트의 버퍼에 저장하도록 한다. 네트워크 장애 발생시 프레임들이 전달되지 않더라도 클라이언트의 버퍼에 저장된 선행 프레임들을 재생함으로써 사용자가 느끼는QoS를 일정한 수준으로 유지할 수 있도록 한다. 실험을 통하여 비디오 스트림의 특성을 분석하였으며 이를 바탕으로 네트워크 상태에 따라 적응적으로 선행하는 프레임을 빠르게 전송함으로써 기존 방식에 비해 QoS를 일정하게 유지할 수 있음을 보였다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.65-66
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• 2005

This paper presents an adaptive satellite communication systems to adapt channel environment. High performance coding and modulation techniques are applied to poor channel condition, otherwise, bandwidth efficient coding and modulation techniques are applied to good channel condition to obtain high transmission rate.

• Journal of electromagnetic engineering and science
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• 제6권2호
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• pp.110-116
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• 2006

A reflective array type surface acoustic wave(SAW) dispersive delay line(DDL) with high time-bandwidth at the V/UHF-band is designed and fabricated for compressive receiver applications. This type of the SAW DDL has the properties of the relative bandwidth of 20 %, the time delay of 49.89 usec, the insertion loss of 38.5 dB and the side lobe rejection of 39 dB. In comparison with a commercial SAW DDL, the insertion loss, amplitude ripple and side lobe rejection are improved by $1.5dB{\pm}0.6dB$ and 4 dB respectively. Using the fabricated SAW DDL, the prototype of the compressive receiver is developed. It is composed of RF converter, fast tunable LO, chirp LO, A/D converter, signal processing unit and control unit. This prototype system shows a fine frequency resolution of below 30 kHz with high scan rate.

• The Journal of the Acoustical Society of Korea
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• 제23권4E호
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• pp.120-124
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• 2004

A new type of high frequency wideband ultrasonic transducer with a separation between a transmitter and a receiver was proposed and its characteristics were simulated using a PSpice model. The piezoelectric ceramic $PbTiO_{3}$ as a transmitter and the piezoelectric copolymer P(VDF- TrFE) as a receiver were used for high sensitivity and wide bandwidth, respectively. The characteristics of the focusing transducer with center frequency of approximately 35MHz fabricated in this study showed very wide bandwidth, which could give an axial spatial resolution better than $30{\mu}m$ in B-mode image for biological tissues.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.328-332
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• 1996

Current controlled inverter is the device which gives fast and accurate current output response for current command Existing current controlled inverters have no way but to take a narrow bandwidth due to resonance of output filter. In this paper, High performance current controlled inverter with multiloop structure is designed and modeling is executed in that basis. This paper realizes the high performance current controlled inverter with the bandwidth above resonant frequency, controls proposed inverter by analog controller, analyzes the performances through simulation and tests 2kW prototype system.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 춘계학술발표대회 논문집 제23권 1호
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• pp.311-314
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• 2004

A new type of high frequency wideband ultrasonic transducer with a separation between a transmitter and a receiver was proposed and its characteristics were simulated using the PSpice model. The piezoelectric ceramic $PbTiO_{3}$ as a transmitter and the piezoelectric copolymer P(VDF-TrFE) as a receiver were used for high sensitivity and wide bandwidth, respectively. The characteristics of a center frequency approximately 40MHz focusing transducer fabricated in this study showed very wide bandwidth which could give an axial spatial resolution better than 30um in the B-mode image for biological tissues.

• Journal of Information Processing Systems
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• 제2권3호
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• pp.159-162
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• 2006

Wireless LANs are becoming more widespread because of the rapid advance of wireless technologies and mobile computers. In this paper, we present the design and implementation of a system to help mobile users to select the most competent AP. By monitoring the network traffic of APs within the local LAN in real time, this system offers the mobile user the network utilizations, locations, and signal strengths of APs online. Based on the information, the user can select a competent AP with a high wireless bandwidth. Finally, we verified the accuracy of monitoring and calculating with regard to the utilizations of APs through real experiments.