• Journal of Digital Contents Society
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• v.19 no.8
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• pp.1545-1554
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• 2018

In order to support the mobility of the wireless devices, at least two APs (Access Points) must be arranged in a single AP area to maintain communication area. In the WLAN (Wireless LAN) environment, seamless handover is one of the most important issues in terms of effective utilization of wireless networks and maximization of services for users. On the other hand, SDN (Software-Defined Networking), which is emerging rapidly in recent years, is revolutionizing network management in terms of flexibility, fine control, and convenience. SDN originally reduces latency time or increases network robustness by real-time flow table control reducing or bypassing paths between switches in LAN-based data centers. In this study, we apply OpenFlow, a SDN platform focused on wired LAN, to a dense WLAN environment using legacy APs to implement and evaluate seamless handover for streaming services of digital contents.

• The Plant Pathology Journal
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• v.24 no.3
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• pp.289-295
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• 2008

RNA-RNA interactions and the dynamic RNA conformations are important regulators in virus replication in several RNA virus systems and may also involved in the regulation of many important virus life cycle phases, including translation, replication, assembly, and switches in these important stages. The 5' non-translated region of Potato virus X(PVX) contains multiple cis-acting elements that facilitate various viral processes. It has previously been proposed that RNA-RNA interactions between various RNA elements present in PVX RNA genome are required for PVX RNA accumulation(Hu et al., 2007; Kim and Hemenway, 1999). This model was based on the potential base-pairing between conserved sequence elements at the upstream of subgenomic RNAs(sgRNAs) and at the 5' and 3' end of RNA genome. We now provide more evidence that RNA-RNA base-pairing between elements present at the 5' end and upstream of each sgRNA is required for efficient replication of genomic and subgenomic plus-strand RNA accumulation. Site-directed mutations introduced at the 5' end of plus-strand RNA replication defective mutant(${\Delta}12$) increasing base-pairing possibility with conserved sequence elements located upstream of each sgRNAs restored genomic and subgenomic plus-strand RNA accumulation and caused symptom development in inoculated Nicotiana benthamiana plants. Serial passage of a deletion mutant(${\Delta}8$) caused more severe symptoms and restored wild type sequences and thus retained possible RNA-RNA base-pairing. Altogether, these results indicate that the RNA element located at the 5' end of PVX genome involved in RNA-RNA interactions and play a key role in high-level accumulation of plus-strand RNA in vivo.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.2
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• pp.1-8
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• 1999

We analyze the transmission performance of WDM system based on cascaded optical add/drop multiplexers. The considered factors degrading the performance in this paper include the intra-channel corosstalk caused from space switches and demultiplexers/multiplexers, the amplified spontaneous emission noise, and the extinction ratio. To ensure the power penalty within 1dB, the extinction ration more than 13dB, the switch corosstalk less than 39dB, and the demultiplexer/multiplexer crosstalk less than 20dB are required. Under the assumption of switch corosstalk less than 30dB, performance degradation due to the ASE noise is dominant compared to the crosstalk. With the fixed decision threshold in an optical receiver, the maximum number of cascaded nodes reduces to a half compared to the case of the optimum decision threshold.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.6
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• pp.131-138
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• 2008

Mobile Ad hoc NETworks (MANETs) refer to autonomous networks in which wireless data communications are established between multiple nodes in a given coverage area without a base station or centralized administration. Because of node mobility and limited battery life, the network topology may changes frequently. Selecting the most reliable path during route discovery process is important to improve performance in ad hoc networks. In this paper, an enhanced routing protocol based on AODV(Ad hoc On-demand Distance Vector routing) by monitoring variation of receiving signal strength is proposed. New metric function that consists of node mobility and hops of path is used for routing decision. For preventing route failure by node movement during data transmission, a new route maintenance named as LRC (Local Route Change) is presented. If the node movement is detected, the routing agent switches path to its neighbor node in LRC. Simulation results show that the performance of the proposed routing scheme is superior to previous AODY protocol.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.9
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• pp.12-20
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• 2013

In this paper, a co-planar waveguide(CPW) fed zeroth-order resonant(ZOR) antenna with frequency reconfigurable radiating structures is fabricated and measured. The unit cell of proposed antenna consists of a series metal-insulator-metal(MIM) capacitor and two shunt line inductors which are shorted through the via. The proposed antenna is designed based on a composite right/left-handed(CRLH) transmission line with two unit cells and it has open ended structure in order to radiate electromagnetic energy mainly on the shunt arm. In order to reduce the antenna size and to exhibit a frequency reconfigurable ability using diode switches four straight strips bent by 90 degrees are used as shunt inductors. The total size of fabricated antenna is $0.22{\lambda}_0{\times}0.16{\lambda}_0$ at zeroth-order resonant(ZOR) frequency. The measured maximum gain and bandwidth (VSWR ${\leq}2$) are 3.1 dBi and 56MHz at ZOR frequency of 2.97 GHz, respectively. This type of antenna can be applied to a frequency reconfigurable antenna system with triple bands.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.6
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• pp.760-770
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• 2016

A 12-bit 750 kS/s Dual-Sampling Successive Approximation Register Analog-to-Digital Converter (SAR ADC) technique with reduced Capacitive DAC (CDAC) is presented in this paper. By adopting the Adaptive Power Control (APC) technique for the two-stage latched type comparator and using bootstrap switch, power consumption can be reduced and overall system efficiency can be optimized. Bootstrapped switches also are used to enhance the sampling linearity at a high input frequency. The proposed SAR ADC reduces the average switching energy compared with conventional SAR ADC by adopting reduced the Most Significant Bit (MSB) cycling step with Dual-Sampling of the analog signal. This technique holds the signal at both comparator input asymmetrically in sample mode. Therefore, the MSB can be calculated without consuming any switching energy. The prototype SAR ADC was implemented in $0.18-{\mu}m$ CMOS technology and occupies $0.728mm^2$. The measurement results show the proposed ADC achieves an Effective Number-of-Bits (ENOB) of 10.73 at a sampling frequency of 750 kS/s and clock frequency of 25 MHz. It consumes only 0.13 mW from a 5.0-V supply and achieves the INL and DNL of +2.78/-2.45 LSB and +0.36/-0.73 LSB respectively, SINAD of 66.35 dB, and a Figures-of-Merit (FoM) of a 102 fJ/conversion-step.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.2
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• pp.113-121
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• 2013

In this paper, quadruple polarized antenna system with a reconfigurable feeding network is presented. The proposed antenna system consists of the reconfigurable feeding network for fourth polarization such as vertical/horizontal linear polarization and right-handed/left-handed circular polarizations or 45 degree tilted vertical/horizontal linear polarization and patch antenna to receive the signals with various polarizations. In order to receive a signal in any direction, the proposed antenna is designed by electrical switches for reconfigurable polarization. The insertion loss of the designed feeding network in the proposed antenna system is approximately 1.2 dB. The measured 3 dB axial bandwidth and gain of the proposed antenna are about 2 % and 4 dBi(c).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.4
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• pp.298-308
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• 2017

This paper presents a Interleaved Buck Converter(IBC) system with Random PWM to reduce electromagnetic noise by harmonics. Swithced mode power supply generally controlled by high switching frequency have a electromagnetic interference(EMI) issue due to the high-voltage/high-current switching to regulate the voltage in buck converter. To solve the problem. we present a novel IBC system with PRBS. IBC system has two active switches with 180 phase difference that controll the cicuit with two PWM signal. IBC system may be disadventageous for the cost due to the addtion of one set of switch, but it has adventages of power distribution, current ripple cancellation, fast transient response, and passive component size reduction. To verify the validity of study, simulation program has been bulit using PSIM and the experimental results of IBC system using RPWM was compared with the conventinal PWM and randomized PWM.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.147-154
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• 2009

This paper presents a grating~integrated SPR (Surface Plasmon Resonance) sensor chip for simple and inexpensive biomolecule detection. The grating-integrated SPR sensor chip has two sensing channels having a nano grating for SPR coupling. An external mirror is used for multi channel SPR sensing. The present sensor chip replaces bulky and expensive optical components, such as fiber-optic switches or special shaped prisms, resulting in a simple and inexpensive wavelength modulated multi-channel SPR sensing system. We fabricate a SPR sensor chip integrated with 835 nm-pitch gratings by a micromolding technique to reduce the fabrication cost. In the experimental characterization, the refractive index sensitivity of each sensing channel is measured as $321.8{\pm}8.1nm$/RI and $514.3{\pm}8.lnm$/RI, respectively. 0.5uM of the target biomolecule (streptavidin) was detected by a $1.13{\pm}0.16nm$ shift of the SPR dip in the 10%-biotinylated sample channel, while the SPR dip in the reference channel for environmental perturbation monitoring remained at the same position. From the experimental results, multi-channel biomolecule detection capability of the present grating-integrated SPR sensor chip has been verified. On the basis of the preliminary experiments, we successfully measured the binding reaction rate for the $2\;nM{\sim}200\;nM$ monoclonal-antibiotin, thus verifying biomolecule concentration detectability of the present SPR sensor chip. The binding reaction rates measured from the present SPR sensor chip agredd well with those from a commercialized SPR sensor.

• Structural Monitoring and Maintenance
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• v.1 no.1
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.