• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.360-370
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• 2010

In this paper, a distributed beamforming problem is considered in an amplify-and-forward (AF) wireless relay network consist of multiple source-destination pairs and relaying nodes. To exploit degree of freedom of the number of beamformers, in the first step, we proposed that the sources transmit their signals through orthogonal channels. During the second step, the relays transmit their received signals multiplied by complex weights to amplify and compensate for phase changes introduced by the backward channels through one common channel. The optimal beamforming vectors are obtained through minimization of the total relay transmit power while the signal-to-interference-plus-noise ratios (SINRs) at the destinations are above certain thresholds to meet a quality of services (QoSs) level. In the numerical example, it is shown that the proposed scheme needs less transmit power for moderate network data rates than other schemes, such as space division multiplexing or time-division multiplexing scheme.

• Journal of the Korea Society of Computer and Information
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• v.17 no.4
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• pp.91-98
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• 2012

A group key exchange (GKE) protocol is designed to allow a group of parties communicating over a public network to establish a common secret key. As group-oriented applications gain popularity over the Internet, a number of GKE protocols have been suggested to provide those applications with a secure multicast channel. Among the many protocols is Yi et al.'s password-based GKE protocol in which each participant is assumed to hold their individual password registered with a trusted server. A fundamental requirement for password-based key exchange is security against off-line dictionary attacks. However, Yi et al.'s protocol fails to meet the requirement. In this paper, we report this security problem with Yi et al.'s protocol and show how to solve it.

• Journal of the Korea Society of Computer and Information
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• v.15 no.3
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• pp.55-63
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• 2010

On Handoff, existing AP search has chosen one of various APs according to signal strength. However IEEE 802.11 uses Medium Access method with CSMA/CA(Carrier Sensing Multiple Access /Collision Avoidance) that competes to obtain a channel by sharing common medium. For that reason, network performance is heavily affected by the number of nodes and network congestion aside from signal strength. Consequently, in this paper we propose the method that choose one AP which ensures more improved network performance and set up a link, reflecting AP network information in Handoff area, on Handoff in the process of AP selection. We also demonstrate through simulation that it gets maximum performance even in the wireless network which many users concurrently access to, and it has considerable effects on aspects of resources and network management by distribution of users.

• Korean Journal of Acupuncture
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• v.28 no.1
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• pp.1-13
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• 2011

Objectives : The object of this study is to evaluate and develop the system that reflects acupoints electrical properties by the multi-frequency using the SPAC (Single Power Alternative Current) stimulation method based on BIA (Bioelectrical impedance method). Methods : The 12 channel meridian impedance measurement system (MIMS) was designed, which sets multi-frequency with 10 steps (1~10kHz). To check acupoints electrical properties, impedance of acupoints were measured from 11 acupoints selected from the LU and ST meridians. Results : Regarding distribution of measurement values by multi-frequencies, we found the lowest response at 1kHz was in common. But frequency bands which represent the highest response at each acupoint were various. Measurement values of each acupoint by multi-frequencies were expressed similar distribution (P<0.05). Also we could check same frequency band which showed the highest response at left/right equal acupoints (P<0.05). Conclusions : Through change of acupoints electrical properties by multi-frequency stimulation, we checked oriental medical diagnostic possibilities by using this system. We would progress variable clinical trials with this system for oriental medical diagnosis.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.1
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• pp.91-100
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• 2010

According to the recent increase in air traffic a more efficient air traffic flow control is required. This paper proposes the algorithm for efficient air traffic flow control. Aeronautical communication environment is different from the common communication environment since it needs a direct communication between stations (or airplanes) and requires a strict priority for safety message. Moreover, the wide area for basic service causes high propagation delay. In this paper, by using existing CSMA/CA Media Access Control (MAC) protocol, we set the message priorities according to air traffic condition (congestion airport area, approach control area, En route area, and ocean area). This prioritization scheme enables the data transmission with higher access probability. Simulation results confirm that our protocol shows better performance in terms of channel efficiency and success probability compared to exisiting CSMA/CA protocol.

• ETRI Journal
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• v.38 no.5
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• pp.981-987
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• 2016

We present a cost-effective dual polarization quadrature phase-shift coherent receiver module using a silica planar lightwave circuit (PLC) hybrid assembly. Two polarization beam splitters and two $90^{\circ}$ optical hybrids are monolithically integrated in one silica PLC chip with an index contrast of $2%-{\Delta}$. Two four-channel spot-size converter integrated waveguide-photodetector (PD) arrays are bonded on PD carriers for transverse-electric/transverse-magnetic polarization, and butt-coupled to a polished facet of the PLC using a simple chip-to-chip bonding method. Instead of a ceramic sub-mount, a low-cost printed circuit board is applied in the module. A stepped CuW block is used to dissipate the heat generated from trans-impedance amplifiers and to vertically align RF transmission lines. The fabricated coherent receiver shows a 3-dB bandwidth of 26 GHz and a common mode rejection ratio of 16 dB at 22 GHz for a local oscillator optical input. A bit error rate of $8.3{\times}10^{-11}$ is achieved at a 112-Gbps back-to-back transmission with off-line digital signal processing.

• Biomedical Science Letters
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• v.26 no.2
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• pp.93-100
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• 2020

Xerostomia is a relatively common oral disease that causes various problems such as pain, discomforted, tissue damage, and infection. When the activity of AQPs, which plays an important role in the microbial channel transmembrane activity in tissues, decreases saliva secretion and the oral cavity dryness occurs. In this study, we observed whether there was a change in tissue through the expression level of AQP-5 in the submandibular gland in the 4-DAMP-induced xerostomia model. First, in order to construct a xerostomia model, 4-DAMP (1 mg/kg) and 20% urethane (0.5 mL/kg) were administered intraperitoneal (i.p.) to experimental animals. To observe the changes in the submandibular gland was excised, H&E staining was performed and protein quantitation analysis was performed using the submandibular tissue to observe the changes in AQP5 protein expression involved in changes in saliva secretion. Also, cinnamaldehyde (5, 12.5, 25 and 50 mg/kg) dissolved in 20% DMSO, in distilled water for each concentration, and then orally administered at a dose of 1 mL for biopsy and protein quantitative analysis. As a result, it was observed that the submandibular tissue, a model of xerostomia was wider than the naïve group. And then western blot analysis, the expression level of AQP5 decreased in the 4-DAMP group compared to the naïve group, and the expression increased in the group administered orally with cinnamaldehyde. Therefore, administration of 4-DAMP resulted in histological changes for xerostomia, and cinnamaldehyde would be a material that can be developed by reducing xerostomia.

• Journal of the Korea Society of Computer and Information
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• v.18 no.6
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• pp.81-89
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• 2013

Currently Internet shopping (or shopping online) is becoming the common consumption channel for Chinese, and it is more likely to continue to grow. Although E-tailers (or the Internet shopping mall) in China is rapidly growing, there are not very many shopping malls that can meet customer satisfaction. E-tailers in Korea analyze the quality evaluation and customer satisfaction of shopping malls. If the Internet shopping that is suitable for Chinese students studying in Korea is built, it is expected to strengthen international competitive power. In this paper, the comparative analysis of Customer satisfaction for Internet shopping between Chinese students studying in Korea and Korean university students is provided. Furthermore, we analyze the customer satisfaction model of Chinese students studying in Korea by using the multi lease square support vector machine that obtains the global optimal solution. Analysis of customer satisfaction of Chinese students studying in Korea are not only used for E-tailers in Korea, but it can strengthen international competitive power.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.211-216
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• 2006

Within the frame of the MERCOSUR (South Common Market), one of the most important goals to achieve by its member states is a better cost effective international cargo transportation system. For this purpose the project of developing a commercial waterway linking the east region of Uruguay with the south of Brazil has been under study for a number of years now. Because of the high costs involved on the development of such waterway, the project has been indefinitely delayed. It is our intention to show an alternative way to reduce the present obstacles by using a budget oriented approach in order to determine the vessel best suited to use on the proposed waterway. So far, every study related to the project has been focused on the amount of work needed to modify the environment in order to accommodate the hardware already available in the region. The conclusions show that the cost of opening and maintaining the required navigation channel is high enough to discourage investment; the added responsibility to take care of any environmental damage incurred during the building and/or operation of the waterway makes searching for a less costly and hazardous option an interesting challenge. The proposed terminal on the Cebollat? River would be located at the heart of the Uruguayan rice growing region. Uruguay exports 90% of its rice production, being Brazil its biggest buyer. Wood chips and clinker are the other types of cargo considered to use the proposed waterway in route to either Brazil or to overseas destinations through the deep water port of Rio Grande. Through the analysis of local data by a Geographical Information System, international regulations regarding inland waterways and shallow draught vessel characteristics, we seek to propose a cost efficient alternative to apply on this particular scenario.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.11
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• pp.2685-2690
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• 2014

WPS determines position via a two-step process. In the construction phase, a radio map is constituted by collecting radio information signals. Positioning procedure is a step of comparing the radio signal newly acquired with the radio map. If the signals collected and the radio map are different the accuracy decreases. Even though the rate of accuracy is different according to positioning algorithms, accuracy drop is an issue common to all WPS systems. Signal strength fluctuation is caused by the malfunction of the device that receives positioning signals, obstruction and channel interference, etc. In this paper, in order to solve the problem caused by signal strength change, we propose a new radio map construction technique. The proposed method is intended to constitute a strong radio map to changes in the signal strength and updated by collecting the signal strength changes to the radio map. The use of this method is expected to enhance the accuracy of WPS by actively counteracting signal fluctuation.