• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.207-210
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• 2001

Recently, the study on the vibration analysis of machinery is greatly important and ESPI is widely used because of its many attractive features. Firstly, ESPI can be used to measure the vibration mode shape and the phase in real-time. Secondly, the conventional measuring methode, such as accelerometers, take much time to measure the whole field of object, but ESPI needs shorter time than other methods. Because ESPI is a field-inspection method. Thirdly, ESPI is a non-contact measuring system. ESPI does not have influence on the specimen. Beyond these features, there are several advantages in ESPI system. In this paper, the Stroboscopic ESPI system is described for measurement of a vibration mode shape. The Stroboscopic ESPI system had been used to visualize the vibration mode shape, in which EO(Electro-Optic)modulator was used to chop CW(Continuous Wavefront)laser. But it was not easy to control EO modulator and quantified the vibration amplitude and the phase of circular metal plate. At first, we found resonant frequency of the specimen by using time-averaged ESPI method. Nextly, the amplitudes of specimen were quantified by using Stroboscopic ESPI and we compare the results which were obtained in several chopping ratio.

• IEMEK Journal of Embedded Systems and Applications
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• v.2 no.2
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• pp.128-136
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• 2007

무선 기술이 가지는 장점인 설치의 편리성, 기동성으로 인하여, ZigBee를 이용한 홈 네트워크 서비스 활용성에 대한 기술개발이 활발히 진행되고 있다. 이러한 유비쿼터스 홈 서비스의 활용성에도 불구하고 ZigBee 기반 홈 기기나 센서 정보의 도청, 비정상적인 패킷의 유통, 메시지 재사용등의 데이터 위/변조 문제와 네트워크 전체를 마비시킬 수 있는 서비스 거부 공격등에 쉽게 노출되어 있다. 본 논문에서는 이에 대한 효과적인 대응과 관리 처리를 위하여, 유비쿼터스 홈 네트워크에서의 ZigBee 기술을 사용할 시에 발생할 수 있는 보안 문제점을 해결하기 위한 ZigBee 기반 End-to-End 보안 기술을 개발하였다. 본 기술 개발의 특징은 ZigBee Device, 코디네이터/게이트웨이 영역은 ZigBee 표준 스펙을 구현하였으며, 응용어플리케이션/서버 영역은 표준 스펙이 정의 되어 있지 않으나, 이 부분을 유비쿼터스 홈 네트워크 서비스 관점에서 설계 및 구현하였다. ZigBee 디바이스가 가지는 하드웨어 자원의 빈약성을 고려하여 최대한 보안 기능을 리소스가 풍부한 응용어플리케이션/서버의 자원 활용에 촛점을 맞췄다.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.181-183
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• 2007

본 논문은 RF 리더기와 RF 태그 상호간의 통신시에 발생할 수 있는 충돌을 감지하고 이를 능동적으로 회피할수 있는 RFID(Radio Frequency IDentification)의 설계에 관한 내용이다. RFID는 사람, 자동차, 화물, 상품 등에 정보를 부가하는 시스템으로 그 부가정보를 무선통신매체를 이용하여 비접족으로 해독하는 시스템으로 기존의 바코드보다 데이터의 전송속도와 용량의 증가 그리고 편리성이 향상되는 장점이 있으나, 동시에 여러개의 RF태그와의 무선통신으로 인한 데이터의 충돌이 발생할 수 있다. 이러한 충돌을 감지하고 이를 적절하게 회피하는 것은 RFID 시스템의 신뢰성을 높이는데 필수적인 요소이다. RFID 태그로 사용되기 위해서는 건전지로 구동될 수 있도록 저전력소모가 요구되며 또한 통신의 시작과 충돌을 파악할 수 있는 캐리어 감지기능이 필수적이다. 본 논문에서는 이러한 조건들을 만족하는 Chipcon 사(社)의 양방향 RF IC를 사용하였다. Chipcon 사(社)의 양방향 RF IC는 다중 주파수 대역의 선택과 변조방식을 시리얼통신을 통해서 손쉽게 변경할 수 있기 때문에 충돌감지시 다양한 회피알고리즘을 상황에 맞게 구현할 수 있다. 본 논문에서는 양방향 RF IC를 사용하여 충돌을 감지하고 회피할 수 있는 RFID시스템을 설계하고 구현하였다.

• Journal of Broadcast Engineering
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• v.1 no.1
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• pp.1-6
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• 1996

Digital DBS service using Korea Sat starts at Korea Telecom's Yong-in transmission site. Total 6 transmitting stations are needed. At each transmitting station, 4 TV programs are compressed and multiplexed using MPEG-2, modulated into IF, RF signals, then finally transmitted through antenna. At DBS transponder, received signal is down converted, amplified and re-transmitted to earth. At receiver, signal is received by 45cm dish antenna, then wanted program is selected, demultiplexed and decoded. Transmission performance of BER lOE-ll is implemented by using FEe coding and QPSK modulation. For pay TV management, conditional access system, smart card and modem are used.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.2
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• pp.226-237
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• 1998

In recent SATCOM systems, transparent transponders are widely used. The transponder is, however, the most vulnerable part in SATCOM systems against jamming interference. All signals within the transponder bandwidth are frequency-converted and retransmitted with IM(intermodulation) products. In this paper, the method is proposed that makes the SJR(Signal-to-Jammer ratio) better. The bandwidth spreading of the user signal can reduce the jammers effects. The geostationary satellite system is modeled to simulate and to certificate the capability of suppression of jammers by DSSS. If signal is partially-overlapped by jammer and PG(processing gain) is 16.9 [dB] for 2ASK jammer and about 16.8 [dB] for QPSK jammer, when BER is $10^{-3}$.

• Composites Research
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• v.17 no.2
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• pp.28-33
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• 2004

Failure detection in a cross-ply laminated composite beam under tensile loading were performed using a fiber Bragg grating (FBG) sensor. A Passive Mach-Zehnder interferometric demodulator was proposed to enhance sensitivity and bandwidth. The proposed FBG sensor system without active device such as a phase modulator is very simple in configuration, easy to implement and enables the measurement of high-frequency vibration with low strain amplitude such as impact or failure signal. Failure signals detected by a FBG sensor had offset value corresponding to the strain shift with vibration at a maximum frequency of several hundreds of kilohertz. at the instant of transverse crack propagation in the 90 degree layer of composite beam.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4B
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• pp.288-299
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• 2012

To ensure data confidentiality and fine-grained access control in business environment, system model using KP-ABE(Key Policy-Attribute Based Encryption) and PRE(Proxy Re-Encryption) has been proposed recently. However, in previous study, data confidentiality has been effected by decryption right concentrated on cloud server. Also, Yu's work does not consider a access privilege management, so existing work become dangerous to collusion attack between malicious user and cloud server. To resolve this problem, we propose secure system model against collusion attack through dividing data file into header which is sent to privilege manager group and body which is sent to cloud server and prevent modification attack for proxy re-encryption key using d Secret Sharing, We construct protocol model in medical environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.725-733
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• 2006

In this paper, we propose an algorithm which makes the frequency of output signal synchronize with frequency of input signal in Equalization Digital On-channel Repeater (EDOCR) system which was proposed to overcome the disadvantage of conventional Digital On-Channel Repeater (DOCR). Also, we verify the algorithm by using the mathematical equivalent model and analysis the performance by implying the algorithm to EDOCR. The main idea is to use the frequency offset information, which comes from carrier recovery in the receiving part of EDOCR, when the demodulated symbol is re-modulated in transmitting part. Based on the proposed algorithm, EDOCR not only makes the output signal synchronized with input signal in frequency but also emit the output signal which satisfies the ATSC transmission standard without additional equipments such as Global Positioning System (GSP).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4C
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• pp.232-240
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• 2011

While the water-filling algorithm is an efficient power allocation method that maximizes the ergodic capacity of adaptive MIMO systems, its excessive residual power causes spectrum loss in real systems employing discrete modulation indices. In this paper we propose new power allocation algorithms that improve the spectral efficiency of MIMO systems by efficiently reallocating the residual power of the water-filling algorithm. We apply the proposed algorithms to the adaptive turbo-coded MIMO system to verify their performance through computer simulation in various environments. Simulation results show that the spectral efficiency of the proposed algorithms is better than that of the water-filling algorithm by about 8.9% at SNR of 20dB in Rayleigh fading environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.3
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• pp.309-315
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• 1998

This paper is analyzed the performance of coded MC-CDMA system using the multi-carrier with narrow band that is suggested to solve ISI and ICI of DS-CDMA system. In this paper, considered channel model is indoor mobile radio communication environment with Rician fading distribution and fading of multi-carrier have mutual independent characteristics. For the performance analysis of MC-CDMA system, first, bit error probability of uncoded system is simulated in the reverse and forward Rician channels. And then, it is simulated that bit error probability of coded MC-CDMA system for users, multicarriers and SNR, using (7,4) Hamming code, (15,7) BCH code and 1/2-convolutional code with 7 constraint length.