• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.8
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• pp.1485-1492
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• 1994

In this paper, we design and implement the Combline Bandpass Filters for the satellite transponder by using the least-squares curve-fitting method. The Combline Bandpass Filters are located front of the mixer and behind of it, which is the component of down converter. Comparing with the filters which have $\lambda$/4 resonance length. Combline Filter has wide range of stop-band by using $\lambda$/8. So, it is useful to the satellite transponder owing to its low mass and small size. The filters described are realized as coupled rectangular coaxial transmission lines. The choice of this type is due to the ease of machining and wide variations in coupling coefficients rather than the use of the round rod resonators. We determine 800 MHz bandwidths for the combline bandpass filters. By using Chebyshev filter function, we design and implement 4-pole combline filters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9C
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• pp.564-572
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• 2011

Distributed video coding (DVC) system has been proposed to reduce encoder complexity by using the correlation of frames in decoders. Since the block based motion estimation operation is not performed in the encoder of DVC system, lapped transforms, in which adjacent two blocks are transformed into one block, can be efficiently used in the DVC system. In this paper, an efficient DVC system using lapped transforms is proposed. The overlapped block motion compensated interpolation is used to produce side information, and the corresponding correlation noise between original Wyner-Ziv frame and side information is modeled. Extensive computer simulations show that the proposed DVC system outperforms conventional DVC systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6B
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• pp.483-488
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• 2012

With the fast growing data traffic, the performance of the convergent overlay network environment under the cognitive networking environment is crucial for the implementation of the efficient network structure. In order to achieve high capacity and reliable link quality in wireless communication of the overlay convergent networks with the cognitive networking based on the advanced capability of the mobile terminal, a Distributed Wireless Communication System (DWCS) can provide the capability of ambient-aware dual cell system's operation. This paper has considered virtual cell: the Dual Virtual Cell (DVC), and also proposes DVC employment strategy based on DWCS network. One is the Active Virtual Cell which exists for user's actual data traffic and the other is the Candidate Virtual Cell which contains a set of candidate antennas to protect user's link quality from performance degradation or interruption. The considered system constructs DVC by using cognitive ability of finding useful virtual signals. Also, for multi-user high-rate data transmission, the DWCS system exploits Space-Time Trellis Codes. The effects of changing environments on the system performance has been investigated thereafter.

• The Journal of the Korea Contents Association
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• v.6 no.1
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• pp.1-7
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• 2006

This paper proposes a new method that reduces the complexity of the combined system, which consists of the selective mapping(SLM) and the partial transmit sequence(PTS) in the Orthogonal Frequency Division Multiplexing(OFDM). In order to reduce the Peak-to-Average Power Ratio(PAPR), many techniques have been developed such as SLM and PTS. and their combined systems. However the method that simply combines PTS and SLM to improve the effectiveness of a system increases the complexity of calculation. The scheme employed in this research suggests a system that combines PTS and SLM reducing the complexity via the N($N=2^n$)-point inverse fast Fourier transforms(IFFT), which uses the decimation in time domain not only to improve PAPR but also to reduce the amount of calculation. The proposed method reduces the complexity by multiplying a phase sequence and a subblock index to the data sequences in the middle of IFFT, which yields an optimal sequence with minimal PAPR. The superiority of the proposed method is demonstrated by simulation results and analysis.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.138-144
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• 2011

The transport phenomena of electron and ion around the electrode have been analyzed, herein the computational program to simulate the electrochemical signal of cyclic voltammetry has been implemented. For the dominant mass-transfer system, the governing equation and its boundary conditions are confined to the semi-infinite diffusion model and the reversible reaction at the electrode. In order to obtain the numerical solutions of cyclic voltammetry, MATLAB was used for the explicit finite difference method. Experimental results from the cyclic voltammetry of electrochemical system(10 mM $K_3Fe(CN)_6$ and 0.1M KCl) upon the ITO glass substrate were compared with the numerical solutions. Present program explains the experimental results fairly well, where they approached the simulated ones closely with deceasing the scan rate. Furthermore, the effects of electrode area, electrochemical reaction constants and transfering coefficients in the cyclic voltammetry were discussed quantitatively.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.451-456
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• 2000

The development of an integrated technology including fabrication of corrosion defect specimens and their practical use is needed to enhance the reliability of eddy current test for nuclear steam generator tubing. In this paper, the necessity and importance are presented from the viewpoint of the structural integrity, simulation specimens for real defects, and experiences from the destructive examination of pulled tubes. The models for several corrosion defects we also briefly introduced, with the scheme for their practical use.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.6
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• pp.581-589
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• 2004

In this study, the capacitive micromachined ultrasonic transducer(cMUT) was developed based on the previous research results. The cross sectional image of the developed cMUT was characterized. To measure the membrane displacement of the cMUT, the Michelson phase modulation fiber interferometer was constructed. The measured membrane displacement was in good agreement with the result of the finite element analysis. To estimate the ultrasonic wave generated by the cMUT, an ultrasonic system including a pulser, receiver and charge amplifier was used. The cMUT developed in this study shows a good performance and hence will be widely used in the non-contact ultrasonic applications.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.21-28
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• 2017

Eddy current array (ECA) technology provides the ability to electronically scan without mechanical scanning for a footprint of probe that consists of several eddy current coils arranged side-by-side and two dimensionally. Compared to single-coil eddy current technology, the ECA technology has a higher inspection speed and reliability because a large area can be covered in a single-probe pass and the obtained images can facilitate data interpretation. In this study, we developed an eddy current array probe with $2{\times}16$ coil arrays and a multiplexer that can select transmit-receive coils sequentially and operate in transmit-receive mode. Surface inspection was performed using this probe for specimens that had various flaws and the characteristics of transmit-receive mode ECA technology was studied through an analysis of the obtained eddy current signals and C-scan images.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.503-503
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• 2012

본 연구에서는 최대전압 600 KV, 최대전류 88 KA, 펄스 폭 60 ns의 특성을 가지는 고전압 펄스 시스템 '천둥'을 이용하여 방전 챔버에 고전압 펄스를 인가하고 $N_2$와 $SF_6$ 혼합기체 종류와 여러 가지 기체압력에서 전기 트리거를 이용한 방전현상을 전기, 광학적으로 연구하였다. 전극은 구리텅스텐 합금재질의 표준전극을 사용하였고, 전극 간격은 10 mm로 고정하였다. 방전 챔버 압력을 100 torr, 1기압, 2 기압에서 실험을 진행하였고, $N_2$에 대한 $SF_6$의 혼합비율을 0~100%까지 변화시키며 실험을 진행하였다. 전기 트리거 신호가 인가된 펄스 방전 스위치의 방전전압 및 방전 기작원리, 트리거 스위칭 지연시간, 트리거 절연파괴 기작원리, 그리고 이때 생성된 플라스마의 전자 온도 및 밀도에 관한 전기광학 특성 등에 관한 기초연구를 수행하였다. 트리거 펄스가 있을 때의 방전개시전압은 트리거 지연시간 20 us 에서 최소가 되는 특성을 보이며, 이때의 SF6 함량에 따른 최소방전전압과 트리거 펄스가 없을 때의 방전전압을 서로 비교하였다. 이를 통하여 A-K gap 10 mm 조건에서 20 us의 트리거 펄스의 지연시간을 가지는 방전 개시전압은 트리거 펄스가 없을 때 전극 간격이 6 mm에 해당되는 방전개시 전압 값을 가짐을 실험적으로 보였다. 이는 트리거 펄스에 의하여 전극 주위에 쉬스가 형성되며, 이로 인한 전극 간격이 가까워지며, 이와 같은 효과 때문에 방전개시전압은 그만큼 낮아지는 것으로 해석 할 수 있다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.9
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• pp.848-857
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• 2011

Vision-based collision avoidance system for air traffic management requires a excellent multiple target detection algorithm under low signal-to-noise ratio (SNR) levels. The track-before-detect (TBD) approaches have significant applications such as detection of small and dim targets from an image sequence. In this paper, two detection algorithms with the TBD approaches are proposed to satisfy the multiple target detection requirements. The first algorithm, based on a dynamic programming approach, is designed to classify multiple targets by using a k-means clustering algorithm. In the second approach, a hidden Markov model (HMM) is slightly modified for detecting multiple targets sequentially. Both of the proposed approaches are used in numerical simulations with variations in target appearance properties to provide satisfactory performance as multiple target detection methods.