• Proceedings of the Korean Society of Computer Information Conference
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• 2014.01a
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• pp.353-354
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• 2014

무선 센서 네트워크(WSN)환경에서는 저가의 센서 노드를 구성하기 위해 배터리, 제한된 에너지 등과 같은 하드웨어적인 제약을 갖고 있다. 특히, 센서 노드의 제한된 에너지는 네트워크 수명과 직접적인 관련이 있기 때문에 네트워크의 수명을 연장하기 위한 효율적인 기법들이 요구되는 실정이다. 이를 위해 본 논문에서는 WSN환경에서 고정 노드와 모바일 노드를 혼용하여 음영지역을 최소화할 수 있는 모바일 노드 이동 기법을 제안한다. 이는 대표 노드를 선정하여 네트워크의 밀도를 제어하고 각 노드들의 거리에 따라 신호 세기를 제어한다. 이를 통해 네트워크 지역의 확장과 각 노드의 에너지를 효율적으로 사용할 수 있다.

• Journal of Power Electronics
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• v.9 no.1
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• pp.26-35
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• 2009

A high efficiency active clamp sepic-flyback converter is presented for fuel cell generation systems. The proposed converter is a superposition of a sepic converter mode and. flyback converter mode. The output voltages of the sepic converter mode and flyback converter mode can be regulated by the same PWM technique with constant frequency. By merging the sepic and flyback topologies, they can share the transformer, power MOSFET and active clamp circuit. The result has outstanding advantages over conventional active clamp DC-DC converters: high efficiency, high power density, and component utilization. Simulation results and experimental results are presented to verify the principles of operation for the proposed converter.

• ETRI Journal
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• v.46 no.4
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• pp.595-603
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• 2024

This paper presents methods for reducing the peak-to-average power ratio (PAPR) of the orthogonal time frequency space (OTFS) signal. These methods mainly consist of two operations: symbol interferometry (SI) and either 𝜇-law or A-law companding. SI spreads the data of one OTFS symbol onto all symbols and is implemented using a simple inverse fast Fourier transform operation on each OTFS symbol. During the second operation, the PAPR of the OTFS signal is significantly reduced. For our performance analysis, the complementary cumulative distribution function, probability density function, and bit error rate are illustrated through simulations performed in MATLAB. The performance is also analyzed using a solid-state power amplifier at the transmitter and compared with OTFS, 𝜇-law-based OTFS, and SI OTFS systems. The results indicate that the proposed OTFS system achieves a low PAPR.

• Journal of Astronomy and Space Sciences
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• v.37 no.2
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• pp.117-129
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• 2020

In a Satellite communication system, a link budget analysis is the detailed investigation of signal gains and losses moving through a channel from a sender to receiver. It inspects the fading of passed on data signal waves due to the process of spreading or propagation, including transmitter and receiver antenna gains, feeder cables, and related losses. The extent of the proposed tool is to make an effective, efficient, and user-friendly approach to calculate link budget analysis. It is also related to the satellite communication correlation framework by building up a graphical interface link analysis tool utilizing STK^® software with the interface of C# programming. It provides better kinds of graphical display techniques, exporting and importing data files, printing link information, access data, azimuth-elevation-range (AER), and simulation is also possible at once. The components of the link budget analysis tool include transmitter gain, effective isotropic radiated power (EIRP), free space loss, propagation loss, frequency Doppler shift, flux density, link margin, elevation plot, etc. This tool can be useful for amateur users (e.g., CubeSat developers in the universities) or nanosat developers who may not know about the RF communication system of the satellite and the orbital mechanics (e.g., orbit propagators) principle used in the satellite link analysis.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.526-529
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• 2002

Various fluoride films on a glass substrate were prepared and characterized in order to determine the best seed layer for a microcrystalline silicon (${\mu}c$-Si) film growth. Among the various group-IIA-fluoride systems, the $CaF_2$films on glass substrates illustrated (220) preferential orientation and a lattice mismatch of less than 0.7% with Si. $CaF_2$ films exhibited a dielectric constant between $4.1{\sim}5.2$ and an interface trap density ($D_{it}$ as low as $1.8{\times}10^{11}\;cm^{-2}eV^1$. Using the $CaF_2$/glass structure, we were able to achieve an improved ${\mu}c$-Si film at a process temperature of 300 $^{\circ}C$. We have achieved the ${\mu}c$-Si films with a crystalline volume fraction of 65%, a grain size of 700 ${\AA}$, and an activation energy of 0.49 eV.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.6
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• pp.2838-2858
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• 2019

Traditional channel models for vehicle-to-vehicle (V2V) communication usually assume fixed velocity in static scattering environment. In the realistic scenarios, however, time-variant velocity for V2V results in non-stationary statistical properties of wireless channels. Dynamic scatterers with random velocities and directions have been always utilized to depict the non-stationary statistical properties of the channel. In this paper, a non-stationary geometry-based cooperative scattering channel model is proposed for multiple-input multiple-output (MIMO) V2V communication systems, where a birth-death process is used to capture the appearance and disappearance dynamic properties of moving scatterers that reflect the time-variant time correlation and Doppler spectrum characteristics. Moreover, our model has more straight and concise to study the impact of the vehicular traffic density on channel characteristics and thus avoid complicated procedure in deriving the analytical expressions of the channel parameters and functions. The numerical results validate our analysis and demonstrate that setting important parameters of our model can appropriately build up more purposeful measurement campaigns in the future.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.1
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• pp.115-122
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• 1987

In this paper, we proposed an improved weakly-coupled power divider(TAP UNIT) for CATV and/or MATV systems, by which the degree of freedom in design and density of coupling interval are signifcantly increased compared with the intrinsic one even though the turn ratios are still of discrete values. On the other hand, the new design theory of a generalized n-way power divider with arbitrary dividing ratios, for CATV and/or MATV systems, which consists of ideal multiwinding transformers and resistors only was presented. Since the circuit elements is not frequency dependent, the proposed power divider is to be of considerably broad bandwidth. Furthermore, the experimental verification has been achieved, and, hence, the validity of the design theory proposed here is confirmed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5434-5441
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• 2012

In the low-density branch line section of domestic railway, the necessity for development of new concept on-board centered train control system which can control the trackside equipment directly from the on-board of train is on the rise since it is problematic in the aspect of efficiency because of its operation in deficits, etc. in accordance with the operation of high-priced wayside equipment being applied to main lines. Accordingly, this paper proposed an on-board control system which can minimize wayside equipment and replace the existing system with it simultaneously by grafting the advanced domestic Information & Communication Technology(ICT), and presented contents of performing confirmation of function through results of concept and detailed design and by building model test environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.6 s.97
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• pp.615-621
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• 2005

In this paper, a model for simulating synthetic aperture radar(SAR) images of earth surfaces. The earth surfaces include forest area, rice crop field, other agricultural fields, grass field, road, and water surface. At first, the backscattering models are developed for bare soil surfaces, water surfaces, short vegetation fields such as rice fields and grass field, other agriculture areas, and forest areas. Then, the SAR images are generated from the digital elevation model(DEM) and digital terrain map. The DTM includes ten parameters, such as soil moisture, surface roughness, canopy height, leaf width, leaf length, leaf density, branch length, branch density, trunk length, and trunk density, if applicable. The scattering models are verified with measurements, and applied to generate an SAR image for an area.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.515-520
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• 2014

In this paper, the protograph-based block low density parity check (LDPC) code, which improves the performance and reduces the encoder/decoder complexity than the conventional Digital Video Broadcasting Satellite Second Generation (DVB-S2) LDPC code used for the marine satellite communication, is proposed. The computer simulation results verify that the proposed protograph-based LDPC code has the better performance in both the bit error rate (BER) and the frame error rate (FER) than the conventional DVB-S2 LDPC code. Furthermore, by analyzing the encoding and decoding computational complexity, we show that the protograph-based block LDPC code has the efficient encoder/decoder structure.