• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.293-301
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• 2006

This paper proposes a control algorithm for STATic synchronous COMpensator(STATCOM), based on Space Vector Modulation(SVM) and Hysteresis Current Controller(HCC) techniques. STATCOM is used to reactive power compensation on a distribution network. The proposed algorithm utilizes the advantages of the fast dynamic response of the hysteresis current control and the reduced switching number of the SVM scheme. The controller determines a set of space vectors from a region detector and applies a space vector. A set of space vectors including the zero vector, to reduce the number of switching, is determined from output signals of two hysteresis comparators. The presented control system was tested with digital simulation in the Borland C++ program and demonstrate the advantage of the proposed hysteresis current controller.

• Convergence Security Journal
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• v.19 no.1
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• pp.3-10
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• 2019

The 5G network is a next-generation converged network that combines various ICT technologies to realize the need for high speed, hyper connection and ultra low delay, and various efforts have been made to address the security vulnerabilities of the previous generation mobile networks. However, the standards released so far still have potential security vulnerabilities, such as USIM deception and replication attack, message re-transmission attack, and race-condition attack. In order to solve these security problems, this paper proposes a new 5G-AKA protocol with PUF technology, which is a physical unclonable function. The proposed PUF-based 5G-AKA improves the security vulnerabilities identified so far using the device-specific response for a specific challenge and hash function. This approach enables a strong white-list policy through the addition of inexpensive PUF circuits when utilizing 5G networks in areas where security is critical. In addition, since additional cryptographic algorithms are not applied to existing protocols, there is relatively little burden on increasing computational costs or increasing authentication parameter storage.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.1
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• pp.24-29
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• 2022

Semantic role labeling task used in various natural language processing fields, such as information extraction and question answering systems, is the task of identifying the arugments for a given sentence and predicate. Predicate used as semantic role labeling input are extracted using lexical analysis results such as POS-tagging, but the problem is that predicate can't extract all linguistic patterns because predicate in korean language has various patterns, depending on the meaning of sentence. In this paper, we propose a korean predicate recognition method using neural network model with pre-trained embedding models and lexical features. The experiments compare the performance on the hyper parameters of models and with or without the use of embedding models and lexical features. As a result, we confirm that the performance of the proposed neural network model was 92.63%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4A
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• pp.502-511
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• 2000

The Gaussian Minimum Shift Keying (GMSK) modulation technique belongs to the class of nonlinear modulation technique, and it is known to be bandwidth efficient. The GMSK modulation is chosen for the digital cellular phone standard by the European Telecommunications Standards Institute (ETSI). In this paper, an efficient method for implementing all digital GMSK modulator is introduced. The proposed modulator is shown to be simple to implement as well as satisfying the required spectral shape recommended by the ETSI.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.11
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• pp.791-803
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• 2001

Mach-Zehnder type traveling-wave Ti：LiNb $O_3$ optical modulators were designed and fabricated. Optimum parameters of optical waveguides were calculated by means of the FDM. Design of CPW traveling-wave electrodes were performed by the FEM in the active region and by the CMM in the input/output section to obtain the conditions of MW effective index and impedance matching. From the measured S parameters, MW characteristics of the traveling-wane electrodes were extracted to be ${\alpha}_m$=0.05426 $\sqrt{f}$, $N_{eff}$=2.2025, and $Z_{c}$=39 ${\Omega}$. The calculated optical response R($\omega$) showed the 3 dB bandwidth of 10 GHz.z..

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1395-1401
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• 2014

In an effort to develop and implement an inertial balance with high performance, the response characteristics of a load cell, which are some of the critical parameters for optimal system design, were evaluated using a sample object of approximately 100 g under microgravity conditions. To this end, a 15-m drop-tower was used to produce microgravity conditions, and the response characteristics of the load cell were investigated in terms of the variations in the magnitude of the deceleration of the sample object, noting that the mass of a living animal should be determined in microgravity. An analysis of the ratio of the inertial forces clearly demonstrated that the average velocity of a load cell plate should be higher than 0.5 m/s to meet the design requirements.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.102-109
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• 2017

The high pressure pump of a diesel injection system compresses the fuel supplied at low pressure into high pressure fuel and maintains the fuel of the common rail at the required pressure level according to the engine operating conditions. The high pressure pump is required to operate normally in order to compress the fuel to a high pressure of 2000 bar during the entire lifetime of the vehicle. Consequently, a suitable design technique, material durability and high precision machining are required. In this study, the high pressure pump simulation model of a 1-plunger radial piston pump is modelled by using the AMESim code. The main simulation parameters are the displacement, flow rate and pressure characteristics of the inlet and outlet valves, cam torque characteristics, and operating characteristics of the fuel metering valve and overflow valve. In addition, the operating characteristics of the pump are simulated according to the parameter changes of the hole diameter and the spring initial force of the inlet valve. The simulation results show that the operation of the developed pump model is logically valid. This paper also proposes a simulation model that can be used for current pump design changes and new pump designs.

• Environmental and Resource Economics Review
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• v.28 no.4
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• pp.645-673
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• 2019

The hypothetical nature of stated preferences can lead to a hypothetical bias that might work as a normative pressure, influencing survey responses. This paper aims to test the impact of social desirability bias by comparing economic estimates based on both subjective and objective valuation questions. The case study is about an urban riverine restoration project in Deajeon, South Korea. As valuation methods both contingent valuation and choice experiments were comparatively applied. Based on a nationally representative sample of 1,000 respondents, the test results offered contrasting conclusions between two test approaches. Accroding to the estimation results based on the conventional valuation, the marginal willingness to pay estimates are 10,500 KRW from CV; and 18,600 KRW for improving water quality, 2,200 KRW for the inside view, 8,900 KRW for the outside view, and 5,800 KRW for biodiversity from CE. A segmentation-based approach is a conventionally used method, which showed a limited impact of social desirability on willingness to pay estimates. The alternative parameterization-based approach measures a model-wide impact of social desirability, proving a significant bias. Although the study positioned a cheap-talk statement before the valuation section of the survey questionnaires, which might have pre-screened the bias, the overall implications of the results suggest a caution in reducing and observing hypothetical bias. There might remain a significant and substantial hypothetical bias even after cheap-talk, particularly in situations with strong social desirability, so that the potential role of objective valuation questions is guaranteed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7C
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• pp.706-714
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• 2009

In this paper, we proposed a burst mode AGC loop and preamble detector applicable for VDL(VHF Digital Link) mode-2 using D8PSK modulation scheme and the performance analysis of proposed schemes is described. Generally the AGC scheme can be divided into two types, continuos and burst mode AGC. The continuos mode is performed well only with an analog feedback AGC loop. But the analog feedback AGC loop is not suitable for burst mode since its gain lock time is more than preamble duration, which causes the preamble detector misses preamble. Hence a fast digital AGC loop is required for burst mode. Also the AGC loop has to be designed with full gain during idle time to detect bursts although the signal level is very low. If the time to acquire gain lock is slow, the preamble detector fail to detect burst due to saturation of a lot of preamble samples. The receiver performance might be down even if the burst was detected because the preamble is used to estimate several parameters need to demodulation at receiver. In this paper we analysed relationships between the AGC loop and preamble detector. we present an AGC loop and preamble detector in burst mode.

• KIPS Transactions on Computer and Communication Systems
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• v.4 no.11
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• pp.369-382
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• 2015

Energy aware server clusters aim to reduce power consumption at maximum while keeping QoS(quality of service) compared to energy non-aware server clusters. They adjust the power mode of each server in a fixed or variable time interval to activate only the minimum number of servers needed to handle current user requests. Previous studies on energy aware server cluster put efforts to reduce power consumption or heat dissipation, but they do not consider energy efficiency well. In this paper, we propose an energy efficient cluster management method to improve not only performance per watt but also QoS of the existing server power mode control method based on autonomous learning. Our proposed method is to adjust server power mode based on a hybrid approach of autonomous learning method with multi level thresholds and power consumption prediction method. Autonomous learning method with multi level thresholds is applied under normal load situation whereas power consumption prediction method is applied under abnormal load situation. The decision on whether current load is normal or abnormal depends on the ratio of the number of current user requests over the average number of user requests during recent past few minutes. Also, a dynamic shutdown method is additionally applied to shorten the time delay to make servers off. We performed experiments with a cluster of 16 servers using three different kinds of load patterns. The multi-threshold based learning method with prediction and dynamic shutdown shows the best result in terms of normalized QoS and performance per watt (valid responses). For banking load pattern, real load pattern, and virtual load pattern, the numbers of good response per watt in the proposed method increase by 1.66%, 2.9% and 3.84%, respectively, whereas QoS in the proposed method increase by 0.45%, 1.33% and 8.82%, respectively, compared to those in the existing autonomous learning method with single level threshold.