• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.3
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• pp.419-425
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• 2001

In land mobile communications, multipath fading is one of the key factors which affect the system performance. Some extensive studies have been carried out to improve the degraded performance under this fading channels. The PSAM channel compensation method using channel fading estimation is widely used and TCM is a combined coding and modulation technique that has been shown to provide significant coding gain without increasing the transmission bandwidth. In this paper, we analyze the performance of PSA-TC-8PSK which combines PSAM and TCM over frequency nonselective fading channels. To estimate channel fading, Wiener filter which minimizes error variance is used as compensation method and we analyze the affects on the system performance of the number of filter taps, period of the pilot symbol frame, and the Doppler frequency. In addition, we consider the symbol timing recovery circuit which can be implemented in the full-digital method and analyze the effects of symbol timing error on the system performance.

• Elastomers and Composites
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• v.52 no.4
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• pp.309-316
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• 2017

In injection molding, the quality of an injection molded product varies greatly depending on the molding conditions. Many researche studies have been conducted on the quality analysis of molded parts according to the molding conditions such as injection pressure, injection temperature, and packing pressure. However, there have not been many studies on the V/P switchover timing. It is known that when a large pressure is applied to a cavity in the packing phase, the cavity pressure is most affected by the packing pressure. In addition, depending on the position (timing) of the packing pressure, it can have a direct influence on quality based on the shrinkage and dimensions of the molded parts. In this study, the change in pressure profile in the cavity according to the V/P switchover position is confirmed. A CAE analysis program (Moldflow) was used to simulate and analyze two models using the PC and PBT materials. In order to compare these results with the actual injection molding results, injection molding was performed for each V/P switchover position, and the correlation between simulation and experiment, especially for the shrinkage of molded parts, was evaluated.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.3
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• pp.207-214
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• 2020

In this paper, we implement linear-quadratic-Gaussian based vector tracking loop (LQG-VTL) instead of conventional extended Kalman filter based vector tracking loop (EKF-VTL). The LQG-VTL can improve the performance compared to the EKF-VTL by generating optimal control input at a specific performance index. Performance analysis is conducted through two factors, frequency thermal noise and frequency dynamic stress error, which determine total frequency tracking error. We derive the thermal noise and the dynamic stress error formula in the LQG-VTL. From frequency tracking error analysis, we can determine control gain matrix in the LQG controller and show that the frequency tracking error of the LQG-VTL is lower than that of the EKF-VTL in all C/N0 ranges. The simulation results show that the LQG-VTL improves performance by 30% in Doppler tracking, so the LQG-VTL can extend pre-integration time longer and track weaker signals than the EKF-VTL. Therefore, the LQG-VTL algorithm is more robust than the EKF-VTL in weak signal environments.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.2
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• pp.71-77
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• 2020

KRS which is subsystem of Korea Augmentation Satellite System (KASS) performs a role of collecting and monitoring GPS signals. In order to generate the accurate correction message, the site which meets the requirements should be selected and verification to meet each requirement should be accompanied. When the sites are selected, the environmental considerations are EMI, clear horizon (CH) and multipath. Of these, EMI and CH can be checked for satisfaction by instrumentation, but multipath error is difficult to predict. Therefore, multipath error analysis for the installation position of actual antenna at each KRS site should be preceded, and multipath scenario should be generated for each location to analyze the effects of the resulting system performance. In this paper, based on satellite signals collected from each KRS sites, the method for analyzing multipath error in each KRS sites is described, and the multipath error is analyzed. Also to perform an analysis of the effects on system performance due to multipath error, multipath error modeling is performed for the generation of simulation scenarios.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.30-36
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• 2016

The battery pack which is a main component of E-scooter needs the cooling system because it is the matter of battery safety in spite of the incresing of charge efficiency due to decress the internal resistence in the condition of high temperature. The purpose of this study is to analyse the effects of cooling methods which is the control of air's inlet and outlet operating timing. When each battery had large temperature deviation in the battery pack, the difference of battery's performance and efficiency were appeared. In this study, the cooling performance of battery pack has been improved by changing the operation timing of inlet and outlet fan, it improved the performance and efficiency of battery. The numerical analysis using a commercial code ANSYS CFX version 17.0 were used for the study.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.386-389
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• 2013

In this paper, for signal integrity analysing high-speed signal between a processor and a DDR2 memory, transient analysis is done and eye diagrams are generated using IBIS models of IC chips and S-parameters of transmission line. From the eye diagrams of such high-speed signals as DQ, DQS/DQSb, Clock, Address and Control, signal quality is assured through measuring timing and voltage margins during setup and hold times and verifying that the over-/under-shoot and the cross points of differential signals satisfy their specifications.

• Journal of ILASS-Korea
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• v.16 no.3
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• pp.126-133
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• 2011

In HCCI Engine, combustion is affected by change of compression speed corresponding to engine speed. The purpose of this study is to investigate the mechanism of influence of engine speed on HCCI combustion characteristics by using numerical analysis. At first, the influence of engine speed was shown. And then, in order to clarify the mechanism of influence of engine speed, results of kinetics computations were analyzed to investigate the elementary reaction path for heat release at transient temperatures by using contribution matrix. In results, as engine speed increased, in-cylinder gas temperature and pressure at ignition start increased. And ignition start timing was retarded and combustion duration was lengthened on crank angle basis. On time basis, ignition start timing was advanced and combustion duration was shortened. High engine speed showed higher robustness to change of initial temperature than low engine speed. Because of its high robustness, selecting high engine speed was efficient for keeping stable operation in real engine which include variation of initial temperature by various factors. The variation of engine speed did not change the reaction path. But, as engine speed increased, the temperature that each elementary reaction would be active became high and reaction speed quicken. Rising the in-cylinder gas temperature of combustion start was caused by these gaps of temperature.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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• pp.983-990
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• 2003

In this paper, a noncoherent code tracking loop is designed for 3GPP MODEM and its performance is analyzed in terms of steady-state jitter variance and transient response characteristics. An analytical closed-form formula for steady-state jitter variance is Int derived for AWGN environments as a general function of a pulse-shaping filter, timing offset, signal-to-interference ratio, and loop bandwidth, together with the analysis on the transient response characteristic of a tracking loop. Based on the analysis, the code tracking loop with variable loop bandwidth that is efficient for full digital H/W implementation is designed and its performance is compared with that of the code tracking loop with fixed loop bandwidth, along with the verification by computer simulations.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.1-9
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• 2022

Global Navigation Satellite System (GNSS) provides location information using signals from multiple satellites. However, a spoofing attack that forges signals or retransmits delayed signals may cause errors in the location information. To prevent such attacks, authentication protocols considering the navigation message structure of each GNSS can be used. In this paper, we analyze the authentication protocols of Global Positioning System (GPS), Galileo, and BeiDou, and compare the performance of Navigation Message Authentication (NMA) of the above systems, using several performance indicators. According to our analysis, authentication protocols are similar in terms of performing NMA and using Elliptic Curve Digital Signature Algorithm (ECDSA). On the other hand, they are different in several ways, for example, whether to perform Spreading Code Authentication (SCA), whether to use digital certificates and whether to use Timed Efficient Stream Loss-tolerant Authentication (TESLA). According to our quantitative analysis, the authentication protocol of Galileo has the shortest time between authentications and time to first authenticated fix. We also show that the larger the sum of the navigation message bits and authentication bits, the more severely affected are the time between authentications and the time to first authenticated fix.

• Journal of the Korea Society of Computer and Information
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• v.15 no.4
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• pp.37-45
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• 2010

A system which needs timely accuracy has to design and to verify correctly about execution-time for reliability. Accordingly, it is necessary for timing analysis tools, and much previous research worked. In timing analysis tool, there are two methods. One is a static analysis, and the other is a measurement based analysis. A static analysis is able to spend time less than a measurement based analysis method, but has low reliability of analysis result caused by hard to estimate time of I/O caused by various hardware. A measurement based analysis can be close analysis to real result, but it is hard to adapt to actual application, and spend a lot of time to get result of analysis. As such, this paper present a software monitoring architecture to supply reliability of static analysis process. In a presented architecture, it can select target as needed measurement through static analysis, and reuse result of measurement exist. Therefore, The architecture can reduce overload of time and performance for measurement, and improve the reliability which is the worst problem of static analysis.