• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.44-51
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• 2002

This paper describes the performance evaluation and analysis of an Orthogonal Frequency-Division Multiplexing (OFDM) system having the least Inter Symbol Interference (ISI) in a multi-path fading channel environment. Wireless Local Area Network (W-LAN) in accordance with IEEE 802.11a and IEEE 802.11b provides high-speed transmission to universities, businesses and other various places. In addition, service providers can offer a public W-LAN service on restricted areas such as a subway. The proliferation of W-LAN has led to greater W-LAN service demands, but problems are also on the rise in offering a good W-LAN service. In particular, urban areas with high radio wave interference and many buildings are vulnerable to deteriorated QoS including disconnected data and errors. For example, when high-speed data is transmitted in such areas, the relatively high frequency generates ISI between Access Points (AP) and Mobile Terminals (such as a notebook computer), leading to a frequency selective fading channel environment. Consequently, it is difficult to expect a goodW-LAN service. The simulation proves that the OFDM system enables W-LAN to implement QoS in high-speed data transmission in a multi-path fading channel environment. The enhanced OFDM performance with 52 sub-carriers is verified via data modulation methods such as BPSK, QPSK and 16QAM based on IEEE 802.11a and punched convolutional codes with code rate of 1/2 and 3/4 and constraint length of 7. Especially, the simulation finds that the OFDM system has better performance and there is no data disconnection even in a mobile environment by applying a single tap equalizer and a decision feedback equalizer to a mobile channel environment with heavy fading influence. Given the above result, the OFDM system is an ideal solution to guarantee QoS of the W-LAN service in a high-speed mobile environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.78-89
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• 1999

In this paper, to improve bandwidth amplitude fluctuation for the broadband signal in indoor propagation environment, we measured and analyzed broadband signal using a vertically polarized, horizontally polarized and circularly polarized antenna, conducting by frequency sweeping method in NLOS (Non-Line-of-Sight) environment. And, to investigate the optimum condition for the improvement of broadband propagation characteristics we also examined the effects of both human motions and transmission antenna height in the NLOS environment. As a result, in the case of NLOS environment, it was found that the amplitude deviation characteristics in frequency bandwidth can be improved by polarization diversity reception. Especially, we found that it is the best effective one to make polarization diversity reception branches, which install the circularly polarized antenna at transmitting end and install the polarized diversity branches received vertical or/and horizontal polarized wave at receiving end. The affection of a human motions is not so much in LOS and NLOS environment, but it can lead to the cause of burst error in indoor digital radio communications as the fade of signal strength become more deeper. And also, when raise the transmitting antenna up to the ceiling, the LOS and NLOS environment could be coexisted. In this case, it can be also inferred that frequency bandwidth amplitude deviation must be fundamentally improved by using polarization diversity reception technique to make the possibility of high transmission rate.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.750-755
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• 2003

This paper proposes a new three-line balun. The equivalent circuit of the proposed three-line balun is presented, and impedance matrix［Z］of the equivalent circuit is derived from the relationship between the current and voltage at each port. The design equation for a given set of balun impedance at input and output ports is presented using［S］parameters, which is transferred fom impedance matrix,［Z］. To demonstrate the feasibility and validity of design equation, multi-layer ceramic(MLC) chip balun operated in the 2.4 GHz ISM band frequency is designed and fabricated by the use of the low temperature co-fired ceramic(LTCC) technology. By employing both the proposed new three-line balun equivalent circuit and multi-layer configuration provided by LTCC technology, the 2012 size MLC balun is realized. Measured results of the multi-layer LTCC three-line balun match well with the full-wave electromagnetic simulation results, and measured in band-phase and amplitude balances over a wide bandwidth are excellent. This proposed balun is very easily applicable to multi-layer structure using LTCC as shown in the paper, and also can be realized with microstrip lines on PCB. This distinctive performance is very favorable for wireless communication systems such as wireless LAN(Local Area Network) and Bluetooth applications.

• Journal of Navigation and Port Research
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• v.26 no.1
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• pp.22-27
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• 2002

The 25 Watt hybrid MIC SSPA has been developed in the frequency rang from 1.6265 GHz to 1.6465 GHz for uplink of INMARST's earth station. To simplify the fabrication process, the whole system is designed of two parts composed of a friving amplifier and a power amplifier. The Motorolas MRF-6401 is used for driving part, the Motorolas MRF-16006 and MRF-16030 is used the power amplifier. We reduced weight and volume of high power amplifier through arranging the bias circuits in the same housing. The realized SSPA has more than 30 dB for gain within 20 MHz bandwidth, and the voltage standing wave ratios(VSWR) of input and output port are less than 1.7, respectively. The output power of 44 dBm is achieved at the 1 dB gain compression point of 106365 GHz These results reveal a high power amplifier of 25 Watt which is the design target. The Proposed SSPA manufacture techniques in this paper can be applied to the implementation of high power amplifiers for some radars and SCPC.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.1
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• pp.90-95
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• 2014

The researchs using brain-computer interface, the new interface system which connect human to macine, have been maded to implement the user-assistance devices for control of wheelchairs or input the characters. In recent researches, there are several trials to implement the speech recognitions system based on the brain wave and attempt to silent communication. In this paper, we studied how to extract features of vowel based on international phonetic alphabet (IPA), as a foundation step for implementing of speech recognition system based on electroencephalogram (EEG). We conducted the 2 step experiments with three healthy male subjects, and first step was speaking imagery with single vowel and second step was imagery with successive two vowels. We selected 32 channels, which include frontal lobe related to thinking and temporal lobe related to speech function, among acquired 64 channels. Eigen value of the signal was used for feature vector and support vector machine (SVM) was used for classification. As a result of first step, we should use over than 10th order of feature vector to analyze the EEG signal of speech and if we used 11th order feature vector, the highest average classification rate was 95.63 % in classification between /a/ and /o/, the lowest average classification rate was 86.85 % with /a/ and /u/. In the second step of the experiments, we studied the difference of speech imaginary signals between single and successive two vowels.

• Journal of Intelligence and Information Systems
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• v.16 no.4
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• pp.173-193
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• 2010

The World Wide Web is transitioning from being a mere collection of documents that contain useful information toward providing a collection of services that perform useful tasks. The emerging Web service technology has been envisioned as the next technological wave and is expected to play an important role in this recent transformation of the Web. By providing interoperable interface standards for application-to-application communication, Web services can be combined with component-based software development to promote application interaction and integration within and across enterprises. To make Web services for service-oriented computing operational, it is important that Web services repositories not only be well-structured but also provide efficient tools for an environment supporting reusable software components for both service providers and consumers. As the potential of Web services for service-oriented computing is becoming widely recognized, the demand for an integrated framework that facilitates service discovery and publishing is concomitantly growing. In our research, we propose a framework that facilitates Web service discovery and publishing by combining clustering techniques and leveraging the semantics of the XML-based service specification in WSDL files. We believe that this is one of the first attempts at applying unsupervised artificial neural network-based machine-learning techniques in the Web service domain. We have developed a Web service discovery tool based on the proposed approach using an unsupervised artificial neural network and empirically evaluated the proposed approach and tool using real Web service descriptions drawn from operational Web services repositories. We believe that both service providers and consumers in a service-oriented computing environment can benefit from our Web service discovery approach.

• Journal of Intelligence and Information Systems
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• v.16 no.2
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• pp.33-54
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• 2010

The World Wide Web is transitioning from being a mere collection of documents that contain useful information toward providing a collection of services that perform useful tasks. The emerging Web service technology has been envisioned as the next technological wave and is expected to play an important role in this recent transformation of the Web. By providing interoperable interface standards for application-to-application communication, Web services can be combined with component based software development to promote application interaction both within and across enterprises. To make Web services for service-oriented computing operational, it is important that Web service repositories not only be well-structured but also provide efficient tools for developers to find reusable Web service components that meet their needs. As the potential of Web services for service-oriented computing is being widely recognized, the demand for effective Web service discovery mechanisms is concomitantly growing. A number of public Web service repositories have been proposed, but the Web service taxonomy generation has not been satisfactorily addressed. Unfortunately, most existing Web service taxonomies are either too rudimentary to be useful or too hard to be maintained. In this paper, we propose a Web service taxonomy generation framework that combines an artificial neural network based clustering techniques with descriptive label generating and leverages the semantics of the XML-based service specification in WSDL documents. We believe that this is one of the first attempts at applying data mining techniques in the Web service discovery domain. We have developed a prototype system based on the proposed framework using an unsupervised artificial neural network and empirically evaluated the proposed approach and tool using real Web service descriptions drawn from operational Web service repositories. We report on some preliminary results demonstrating the efficacy of the proposed approach.

• Korean Journal of Social Welfare Studies
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• v.40 no.3
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• pp.327-348
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• 2009

The purpose of this study is to understand the diverse lifestyles of Korean older adults by analyzing the consumption pattern of older households and its determinants. The 9th wave of the Korea Labor and Income Panel Study(KLIPS) data was used for analysis. The twenty consumption items provided by the dataset was reduced to thirteen according to the consumption purpose inherent in the item. K-means cluster analysis and multinomial logistic regression was employed to categorize the consumption pattern of older households and to analyze the determinants. The results are as follows. The consumption pattern of Korean older adults was clustered into six distinctive groups named Breadwinner, Leisure-time pursuer, Friendly outgoes, Daily-life survivor, Illness sufferer and Shelter seeker. Breadwinner, Leisure-time pursuer and Friendly outgoes were lifestyles that earn and spend more compared to the other three. Nevertheless, they differed according to the family size, indicating that the parenting burden might have direct influence on the lifestyle of Korean older adults. Older adults without parenting burden and with high level of education and economic capacity were likely to show Friendly outgoes lifestyle. On the other hand, Daily-life survivor, Illness sufferer and Shelter seeker showed lower level of spending, indicating that for those lacking in economic capacity, urgent needs such as medical need or housing need dominates the lifestyle. The results call for adequate custom policies that best fit the needs of older adults.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.331-337
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• 2003

This paper represents 50 ㎓ narrow band pass filters for fiber optical communication fabricated by dual ion beam sputtering method. We have analyzed the characteristics of the TA$_2$ $O_{5}$ and $SiO_2$ single layers in order to optimize the process conditions for the 50 ㎓ narrow band pass filters, and controlled the film thickness uniformity to less than 0.1 nm deviation by dual peak spike filter pre-deposition. We designed and fabricated 50 ㎓ narrow band pass filters that consist of 216 layers including 4 cavities based on quarter wave optical thickness. Class substrates with high thermal expansion coefficients were used to reduce the film stress. Anti-reflection coating at the rear side of the substrate was also needed to reduce the optical thickness errors of the Optical Monitoring System caused by multiple beam interference between the front side and the rear side of substrate. The optical characteristics of this 50 ㎓ narrow band pass filters are insertion loss of 0.40 ㏈, pass band ripple of 0.20 ㏈, and pass bandwidth at -0.5 ㏈ of 0.20 nm. and isolation bandwidth at -25 ㏈ of 0.6 nm, which satisfy specifications of dense WDM system in fiber optical communications.tions.

• Journal of Family Resource Management and Policy Review
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• v.25 no.4
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• pp.87-99
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• 2021

The life of middle-aged one-person households is rising as one of the most important family policy issues in Korean society. In Japan, even in multi-person households, the issues of middle-aged sons and daughters living with their old parents have been a concern. Data are from the 13^th wave of the Korea Welfare Panel Study analyzing 482 middle-aged singe males regardless of their past marital status. The purpose of this study is to investigate the effects of human capital and social capital on the life satisfaction of middle-aged single persons by comparing one-person and multi-person households, respectively. Major results were as follows: First, the level of human capital of one-person households of middle aged males was lower than their counterparts in multi-person households. Second, the level of social capital in the group of divorced or widowed, nonhouseholder middle-aged males in multi-person households was lower than their counterparts in one-person households. Third, the effects of human capital and social capital on life satisfaction was significantly different by their marital status and household types in the group of middle-aged single males. Based on the results, policy implications on the community programs for middle-aged males including not only one-person households but also multi-person households were discussed.