• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3600-3607
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• 2009

This paper describes the development of a power sensor for wireless signal over the ultra wideband range of 300~3800MHz with the detecting range of 150mW~150W. The proposed power sensor fundamentally has the function of not only detecting wireless power, but recognizing frequency and measuring VSWR. The development of the power sensor is completed through the design of dual directional coupler, design of power detector block which produces DC data using the corresponding RF input power level, and establishment of collecting the exact calibration data. The dual directional coupler has the operating frequency of 300~3800MHz with the 0.085dB of insertion loss, and directivity of 30dB at least at 3800MHz. The developed power sensor has the capability of power sensing with less than 0.25dB of resolution as well as measuring VSWR of 1.17~1.96 under the practical operating situation of very high power up to 150W at 300~3800MHz.

• The KIPS Transactions:PartC
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• v.15C no.6
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• pp.573-586
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• 2008

The improved performance and miniaturization of computer and the improvement of wireless communication technology have enabled the emergence of many high quality services. Among them multicast services are receiving much attention and their usage is increasing due to the increase of Internet multimedia services such as video conference, multimedia stream, internet TV, etc. Security plays an important role in mobile multicast services. In this paper, we proposed a secure multicast protocol for a hierarchical micro-mobility environment. The proposed secure multicast protocol provides security services such as authentication, access control, confidentiality and integrity using mechanisms including symmetric/asymmetric key crypto-algorithms and capabilities. To provide forward/backward secrecy and scalability, we used sub-group keys based on the hierarchical micro-mobility environment. With this security services, it is possible to guard against all kinds of security attacks performed by illegal mobile nodes. Attacks executed by internal nodes can be thwarted except those attacks which delete packet or cause network resources to be wasted. We used simulator to measure the performance of proposed protocol. As a result, the simulation showed that effect of these security mechanisms on the multicast protocol was not too high.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.54-67
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• 2000

It is known that the performance of a DS-CDMA system mainly depends on Multiple Access Interference(MAI). The effect of MAI in a reverse link is larger than that of a forward link because of the absence of orthogonality among mobile stations. In this paper we investigate the effect of synchronous transmission in the reverse link, which is compared to the performance of asynchronous transmission in the reverse link. In addition, we consider the effect of interference from Mobile Stations(MSs) in a hand-over region. That is, if we assume that a MS is moving from a serving base station(sowing BS) to a target base station(target BS), the signal of the MS is not orthogonal with the signals of all other MSs within the target BS because the MS is only synchronized with the serving BS. Finally we suggest an interference cancellation scheme to reduce the interference from MSs in the region of hand-over, which can be one of solutions for the capacity degradation due to interference from the MSs in the hand-over region in reverse link synchronous transmission.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.10A
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• pp.922-929
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• 2005

This paper proposes an adaptive pilot beacon equipment for mobile communication systems based on direct spread spectrum technology which generates the pilot channel for handoff between base stations by using the information acquired from the downstream wireless signal regarding the overhead channel information. Such an adaptive pilot beacon equipment will enable low power operation since among the wireless signals, only the pilot channel will be generated and transmitted. The pilot channel in the downstream link of the CDMA receiver is used to acquire time and frequency synchronization and this is used to calibrate the offset for the beacon, which implies that time synchronization using GPS is not required and any location where forward receive signal can be received can be used as the installation site. The downstream link pilot signal searching within the CDMA receiver is performed by FPGA and DSP. The FPGA is used to perform the initial synchronization for the pilot searcher and DSP is used to perform the offset correction between beacon clock and base station clock. The CDMA transmitter the adaptive pilot beacon equipment will use the timing offset information in the pilot channel acquired from the CDMA receiver and generate the downstream link pilot signal synchronized to the base station. The intermediate frequency signal is passed through the FIR filter and subsequently upconverted and amplified before being radiated through the antenna.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.160-173
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• 2013

In this paper, we propose a new visual odometry technique by combining a forward-looking stereo camera and a backward-looking monocular camera. The main goal of the proposed technique is to identify the location of a moving vehicle which travels long distance and comes back to the initial position in urban road environments. While the vehicle is moving to the destination, a global 3D map is updated continuously by a stereo visual odometry technique using a graph theorem. Once the vehicle reaches the destination and begins to come back to the initial position, a map-based monocular visual odometry technqieu is used. To estimate the position of the returning vehicle accurately, 2D features in the backward-looking camera image and the global map are matched. In addition, we utilize the previous matching nodes to limit the search ranges of the next vehicle position in the global map. Through two navigation paths, we analyze the accuracy of the proposed method.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.144-149
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• 1999

The two distinct adsorption sites and transition between the under and over-potentially deposited hydrogen (UPD H and OPD H) on the polycrystalline iridium (poly-Ir) surface in the 0.2 M LiOH electrolyte have been studied using the phase-shift method. At the forward and backward scans, the UPD H peak occurs on the cyclic voltam-mogram. The transition region on the phase-shift profile or the Langmuir adsorption isotherm occurs at ca. -0.80 to -0.95 V vs. SCE. At the transition region (-0.80 to -0.95 V vs. SCE), the equilibrium constant (K) for H adsorption transits from $7.9\times10^{-2}\;to\;1.5\times10^{-4}$ and vice versa. Similarly, the standard free energy $({\Delta}G_{ads})$ of H adsorption transits from 6.3 to 21.8kJ/mol and vice versa. The UPD H and OPD H on the poly-Ir surface act as two distinguishable electroadsorbed H species. Both the UPD H peak and the transition region are attributed to the two distinct adsorption sites of the UPD H and OPD H on the poly-Ir surface.

• Transactions of the KSME C: Technology and Education
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• v.3 no.3
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• pp.217-223
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• 2015

The patterning of microbead in microfluidics channel is a practical technique for application in bio and medical areas. An approach is described for a direct patterning of magnetically active microbeads in microfluidic devices without inner structure. Local magnet arrangements - flat arrangement and stack arrangement - contacting same poles or opposite poles of magnet were utilized for generating trapping magnetic fields. The arrangement of magnets contacting same poles generated isolated patterns by repelling of magnetic field. The flat arrangement of vertically reverse magnet arrays shaped trapping patterns repelling magnetic field line between same poles. Spatially, the stack compositions of magnet arrangements allow diverse isolated trapped patterns of magnetic particles. Trapped magnetic particles in fluidic channels were stable on the $18m{\ell}/hr$ flow conditions and magnetic force of 1.08 mT in the all experiments. This experimental study suggests the simple and versatile methods to pattern magnetic particles, and has potential of wide application to bio and medical area.

• Journal of the Korea Society of Computer and Information
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• v.19 no.3
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• pp.63-71
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• 2014

We analyze the execution time of Reed-Solomon coding, which is the MAC-layer forward error correction scheme used in CDMA2000 1xEV-DO broadcast services, under different air channel conditions. The results show that the time constraints of MPEG-4 cannot be guaranteed by Reed-Solomon decoding when the packet loss rate (PLR) is high, due to its long computation time on current hardware. To alleviate this problem, we propose three error control schemes. Our static scheme bypasses Reed-Solomon decoding at the mobile node to satisfy the MPEG-4 time constraint when the PLR exceeds a given boundary. Second, dynamic scheme corrects errors in a best-effort manner within the time constraint, instead of giving up altogether when the PLR is high; this achieves a further quality improvement. The third, video-aware dynamic scheme fixes errors in a similar way to the dynamic scheme, but in a priority-driven manner which makes the video appear smoother. Extensive simulation results show the effectiveness of our schemes compared to the original FEC scheme.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.308-315
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• 2009

Wave-current interaction due to strong ambient currents causes to alter wave properties such as wave height, wave profile and wave spectrum. In this study we first examined the SWAN model's applicability by comparing with an analytical solution of Suh et al. (1994) for wave-current interaction in finite water-depth. Numerical experiments using SWAN model have been conducted for Garolim Bay to estimate the design waveheights influenced by strong tidal currents. For the design wave periods of 8~10 sec, the design wave height of 3 m in NNW direction was increased by up to 40% when the incident waves encounter the opposing currents of 1.4 m/s while the wave height was reduced by 26% due to the following currents of 1.1 m at the bay mouth. This result indicates that the effect of wave-current interaction must be included to determine the design wave height if there exists a strong current.

• The Journal of Engineering Geology
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• v.26 no.3
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• pp.403-411
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• 2016

A three-dimensional finite element analysis was conducted to analyze the predictable distances of a fault zone by using longitudinal displacement on tunnel face, trend line, L/C ratio, and C/C₀ ratio at tunnel crown. The analysis used 28 numerical models with various fault attitudes. As a result, those faults that have drives with dip could be predicted earliest in L/C and C/C₀ ratio analysis. And those faults that have drives against dip could be predicted earliest in L/C ratio and longitudinal displacement analysis. In addition, the fault zone ahead of tunnel was predicted in most models by using longitudinal displacement, trend line, L/C ratio, and C/C₀ ratio. However, the longitudinal displacement among these methods may be most usefully predict a fault zone since it is displacements can be measured immediately after tunnel excavation.