• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.10
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• pp.73-82
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• 2015

This paper proposes an ripple reduction algorithm and analyzes the effects of offset and scale errors generated by voltage sensor while measuring grid voltage in grid-tied single-phase inverters. Generally, the grid-connected inverter needs to detect the phase angle information by measuring grid voltage for synchronization, so that the single-phase inverter can be accurately driven based on estimated phase angle information. However, offset and scale errors are inevitably generated owing to the non-linear characteristics of voltage sensor and these errors affect that the phase angle includes 1st harmonic component under using SRF-PLL(Synchronous Reference Frame - Phase Locked Loop) system for detecting grid phase angle. Also, the performance of the overall system is degraded from the distorted phase angle including the specific harmonic component. As a result, in this paper, offset and scale error due to the voltage sensor in single-phase grid connected inverter under SRF-PLL is analyzed in detail and proportional resonant controller is used to reduce the ripples caused by the offset error. Especially, the integrator output of PI(Proportional Integral) controller in SRF-PLL is selected as an input signal of the proportional resonant controller. Simulation and experiment are performed to verify the effectiveness of the proposed algorithm.

• Journal of Communications and Networks
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• v.8 no.1
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• pp.38-48
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• 2006

A synchronous multicarrier (MC) code-division multiple access (CDMA) system using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) for the downlink mobile communication system operating in a frequency selective Rayleigh fading channel is analyzed. Both carrier frequency offset and timing offset are considered in the analysis. Bit error rate performance of the system with both equal gain combining and maximum ratio combining are obtained. The performance is compared to that of the conventional system using correlation receiver. It is shown that when subcarrier number is large, the system using IFFT/FFT has nearly the same performance as the conventional one, while when the sub carrier number is small, the system using IFFT/FFT will suffer slightly worse performance in the presence of carrier frequency offset.

• Journal of the Korea Society for Simulation
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• v.4 no.2
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• pp.31-40
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• 1995

A hybrid simulation model consists of real physical entities as well as simulated ones. It also contains logical processes for decision making for each operation units, a group of the entities. During the execution of such simulations, the physical and the logical processes consume real clock time while the activity durations of the simulated ones are generated. Due to the inherent chracteristics of the subjects of the communication channels. Since one can not undo an real event already taken place, the traditional central clock approach is used for the synchronization of the events(Kim[6]). However, there are still chances of causality errors due to the randomness in the communication delays. This error is not found in the distributed pure simulations. This paper explains the error in details and proposes a prevention scheme that is simple to implement.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.11a
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• pp.21-23
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• 2017

본 논문에서는 스펙트럼 감지 무선 인지 네트워크에서 동기화 에러가 존재하는 환경을 고려한다. 동기화에러가 존재 할 때 주어지는 오검출 확률(miss detection probability)을 이용하여 일차 사용자와 이차 사용자들 간의 충돌 확률(collision probabliyt)를 유도한다. 유도된 수식을 몬테 카를로 모의실험(Monte Carlo simulation)을 통해 확인한다.

• 전자공학회논문지 IE
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• v.46 no.4
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• pp.78-82
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• 2009

We analyze an analysis of the performance of OFDM(Orthogonal Frequency Division Multiplexing) under multipath channel conditions, and to allow for different OFDM configurations. In this paper, the effects on multipath delay spread, peak power dipping, channel noise and time synchronization errors for the OFDM Signals are analyzed.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.274-276
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• 2001

A simple current controller for three-phase PWM power inverters using 3-level comparator is presented. All voltage vectors are accurately selected in order to minimize the current error using two three-level comparators and ${\alpha}-{\beta}$ current reference frame. The proposed algorithm have fast response and low current errors. This current controller is improved synchronization problem and increased the voltage utilization value. Usefulness of propose method are verified on the simulation result using Matlab/Simulink.

• ETRI Journal
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• v.36 no.4
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• pp.545-553
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• 2014

This paper proposes an algorithm to sense orthogonal frequency-division multiplexing (OFDM) signals in cognitive radio (CR) systems. The basic idea behind this study is when a primary user is occupying a wireless channel, the covariance matrix is non-diagonal because of the time domain cross-correlation of the cyclic prefix (CP). In light of this property, a new decision metric that measures the power of the data found on two minor diagonals in the covariance matrix related to the CP is introduced. The impact of synchronization errors on the signal detection is analyzed. Besides this, a likelihood-ratio test is proposed according to the Neyman-Pearson criterion after deriving probability distribution functions of the decision metric under hypotheses of signal presence and absence. A threshold, subject to the requirement of probability of false alarm, is derived; also the probabilities of detection and false alarm are computed accordingly. Finally, numerical simulations are conducted to demonstrate the effectiveness of the proposed algorithm.

• International journal of advanced smart convergence
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• v.11 no.3
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• pp.56-63
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• 2022

Cyber-physical systems (CPSs) can solve real problems by utilizing closely connected resources in the cyber world. Most problems arise because the physical world is uncertain and unpredictable. To address this uncertainty, information pouring from numerous devices must be collected in real-time, and each interconnected device must share the information. At this time, CPS must meet timing-related techniques and strict timing constraints that can deliver accurate information within predefined deadlines in order to interact closely beyond simply connecting the cyber and physical worlds. Timing errors in safety-critical systems, such as automobiles, aviation, and medical systems, can lead to catastrophic disasters. In this paper, we classify timing problems into two types: real-time delay and synchronization problems. The results of this study can be used in the entire process of CPS system design, implementation, operation, verification, and maintenance. As a result, it can contribute to securing the safety and reliability of CPS.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.27 no.2
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• pp.139-147
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• 2009

The gravity data collected and reserved in Korea is seriously biased in its distribution. That is, only the west-southern part of the peninsula including Chungcheong and Jeonla area has dense distribution while only a part is covered in Gyoungsang area. Especially, the low density of the gravity data in mountainous area basically limits the accuracy of the gravimetric geoid in Korea. As one of the solution to overcome the problem, an airborne gravity survey were conducted from Dec. 2008 $\sim$ Jan. 2009. In this study, free-air gravity anomaly derived from the airborne gravity data which has consistent quality are presented. The data processing for the airborne gravity is composed of several corrections of errors such as errors from gravity measurement, errors from flight dynamics, errors from GPS, and errors from time synchronization. We presented detailed explanations on the data processing with the final cross-over results. The free-air anomaly from airborne gravity finally shows the cross-over accuracy of 2.21mGal which reflects the precision of each track is 1.56mGal. It is expected that the result from this study will play a role as input data in precision geoid determination with ground and ship-borne gravity data after appropriate fusion process.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.108-116
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• 2005

Synchronizations of intra${\cdot}$intermedia for the lecture presentation in distributed multimedia environments are difficult to guarantee accurate temporal relationship between media, due to the asynchronous errors such as the delay or loss of transferred data or the transmission characteristics of each media. The jitter phenomenon occurs when the network delay has the media arrival rate abnormal because the intra-media synchronization reflects the presentation rate. And the cumulative effective of jitters on a per media stream basis results in a skew. This phenomenon cause confusion to contents recognition of learners due to network delay and can not provide effective interaction of sender and receiver in the distance education. Therefore, this paper can be solution to problems due to network delay by maintaining the requirements of temporal relationship between more than one media. And this paper enables to suggest the inter-media synchronization method that is subject to be influenced by presentation rate, and to implement lecture presentation system for distance education.