• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.361-366
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• 2009

We propose the performance enhancing method optimization of an asynchronous 2.5 Gbps/1.25 Gbps optical subscriber network with inverse RZ (Return to Zero) coded downstream and NRZ (Non Return to Zero) upstream re-modulation by adjusting threshold level control of a receiver. We theoretically analyze the BER (Bit Error Rate) performance by modeling the occurrence of BER by simulation with MATLAB according to the types of downstream data. The results have shown that the normalized threshold level in an optical receiver could be saturated at 1/3 as the SNR (Signal to Noise Ratio) increases. The needed SNR for obtaining the BER $10^{-9}$ can be reduced by $\sim$5 dB by optimizing the normalized threshold level at 1/3 instead of by using the conventional receiver with threshold level of 0.5. The proposed system can be a useful technology for asynchronous optical access networks with asymmetric upstream and downstream data rates, because the improved minimum receiving power could replace a light source with a source with lower power and lower cost in an OLT (Optical Line Termination).

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.6
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• pp.11-16
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• 2017

Multi-level holographic data storage requires modulation codes for avoiding two dimensional inter-symbol interference (2D-ISI). Modulation codes can remove the fatal ISI pattern of neighboring the largest and the smallest symbols. In this paper, we propose a 4-level 4/6 modulation code and its trellis encoding for error correction. The proposed 4/6 modulation code prevents that the symbol 0 and 3 are not adjacent in any direction. Also, we compare the proposed modulation code with the same code rate modulation codes for four-level holographic data storage.

• Journal of Electrical Engineering and Technology
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• v.6 no.5
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• pp.595-604
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• 2011

A three-phase three-level shunt active filter controlled by fuzzy logic current controller which can compensate current harmonics generated by nonlinear loads is presented. Three-level inverters and fuzzy controllers have been successfully employed in several power electronic applications these past years. To improve the conventional pwm controller performance, a new control scheme based on fuzzy current controller is adopted for three-level (NPC) shunt active filter. The scheme is designed to improve compensation capability of APF by adjusting the current error using a fuzzy rule. The inverter current reference signals required to compensate harmonic currents use the synchronous reference detection method. This technique is easy to implement and achieves good results. To maintain the dc voltage across capacitor constant and reduce inverter losses, a proportional integral voltage controller is used. The simulation of global system control and power circuits is performed using Matlab-Simulink and SimPowerSystem toolbox. The results obtained in transient and steady states under various operating conditions show the effectiveness of the proposed shunt active filter based on fuzzy current controller compared to the conventional scheme.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.35-44
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• 2014

Sound pressure levels in the receiving room while testing airborne sound insulation performance are varied by the measuring points. This may increase the measurement error, then decrease the measurement reliability. With this reason the research has carried out on the method to reduce deviations of sound pressure level in the ISO type rectangular laboratory focusing on the measurement of airborne sound insulation performance. Tests were made to see the effect of sound absorption in the receiving room, loudspeaker locations, microphones locations and flanking transmission path. Consequently, it was resulted that sound absorption in the receiving room and the loudspeaker location have influence on the sound level deviations especially in the low frequency. The microphone location was very important to get measurement reliability. The effective measuring point, which the sound level difference with average sound pressure level is within 2 dB, could yield most reliable average sound pressure level. Therefore it is necessary to find the effective measuring points in the receiving room. Flanking transmission path should be sealed using sound absorber or magnet etc. to prevent from lowering the sound insulation performance.

• Cross-Cultural Studies
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• v.22
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• pp.303-327
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• 2011

This study aims to uncover the learner's language proficiency shown in the writing data of Chinese elementary/intermediate level learners. Language proficiency of the learners acquired by error analysis provides only partial information, and thus this study analyses the interlanguage of Korean learners in terms of 'Mean Length of Utterance, MLU' to discover the overall aspect of learner's language proficiency more symmetrically. The analysis of vocabulary area is to be enforced after generally studying the learner's language development aspect in accordance with MLU-m(orpheme) and MLU-(w)ord found in compositions by Chinese speaking Korean language learners. In terms of MLU, it has been slightly increased as the level of proficiency between elementary level and intermediate level learners; however, the morpheme seemed to be difficult to use, since the difference between Chinese learners and Korean university students has been notably shown. Vocabulary diversity, using aspect for each word class, and using aspect of the predicate are studied for vocabulary area; more various and numerous vocabulary tend to be used as the level of proficiency increases. In terms of predicate use, Chinese learners use less numerous vocabulary types.

• Korean Journal of Remote Sensing
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• v.37 no.2
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• pp.221-232
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• 2021

This study analyzed co-registration results according to the geometric processing level of reference image, which are Level 1R and Level 1G provided from KOMPSAT-3 and KOMPSAT-3A images. We performed co-registration using each Level 1R and Level 1G image as a reference image, and Level 1R image as a sensed image. For constructing the experimental dataset, seven Level 1R and 1G images of KOMPSAT-3 and KOMPSAT-3A acquired from Daejeon, South Korea, were used. To coarsely align the geometric position of the two images, SURF (Speeded-Up Robust Feature) and PC (Phase Correlation) methods were combined and then repeatedly applied to the overlapping region of the images. Then, we extracted tie-points using the SURF method from coarsely aligned images and performed fine co-registration through affine transformation and piecewise Linear transformation, respectively, constructed with the tie-points. As a result of the experiment, when Level 1G image was used as a reference image, a relatively large number of tie-points were extracted than Level 1R image. Also, in the case where the reference image is Level 1G image, the root mean square error of co-registration was 5 pixels less than the case of Level 1R image on average. We have shown from the experimental results that the co-registration performance can be affected by the geometric processing level related to the initial geometric relationship between the two images. Moreover, we confirmed that the better geometric quality of the reference image achieved the more stable co-registration performance.

• Journal of the Korean earth science society
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• v.31 no.1
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• pp.95-105
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• 2010

The purpose of this study lies in applying generalizability theory depending on the aim of the usage of GALT to analyze the sources of error of single-facet considering item and person only and to analyze the sources of error of multi-facet considering item, person and domain. The study was conducted with 1016 students of local elementary, middle, and high schools. The 21 items of a full version were answered for 40 minute and then the 12 items of short version were sampled to analyze reliability using generalizability theory. Both the full version and the short version of the items were analyzed using Cronbach's alpha for data analysis, and we applied generalizability theory and separate $p{\times}i$ design and $p{\times}(i:h)$ design, G study and D study were performed. Results of analysis are as follows: First, the result of D study after $p{\times}I$ design both on the full version and the short version showed that in the case of the full version, the generalizability coefficient was 0.87 exceeding a normal level of 0.80, and the normal level of generalizability coefficient was achieved in 13 items as well. In case of short version, when 12 items were evaluated, generalizability coefficient was 0.77 not reaching the normal level, and the normal level was achieved in case of more than 15 items. Second, the result of D study after $p{\times}(I:H)$ design on the short version showed that once one domain consists of 2 items in 6 domains, generalizability coefficient was 0.71 which is lower than the normal level of 0.80, the normal level was achieved in more than 5 item cases.

• Journal of the Korean Institute of Intelligent Systems
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• v.3 no.2
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• pp.18-35
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• 1993

The water level control system of the steam generator in a pressurized water reactor and its control problems are analysed. In this work the stable control strategy during the low power operation and transient states is studied. To solve the problem, a fuzzy logic control method is applied as a basic algorithm of the controller. The control algorithm is based on the operator's knowledges and the experiences of manual operation for water level control at the compact nuclear simulator set up in Korea Atomic Energy Research Institute. From a viewpoint of the system realization, the control variables and rules are established considering simpler tuning and the input-output relation. The control strategy includes the dynamic tuning method and employs a substitutional information using the bypass valve opening instead of incorrectly measured signal at the low flow rate as the fuzzy variable of the flow rate during the pressure control mode of the steam generator. It also involves the switching algorithm between the control valves to suppress the perturbation of water level. The simulation results show that both of the fine control action at the small level error and the quick response at the large level error can be obtained and that the performance of the controller is improved.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.60-67
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• 2014

The purpose of this study is to suggest a new concept of the absolute sound level system in order to basically solve all the irrational aspects from the mastering stage to the output stage during the process of producing a sound source. Through this absolute sound level system, all the input absolute sound levels of sound sources become standardized based on 60 dB(S), and then sound source producers can implement a sound level they intend by using the differential sound level tag. Besides, by matching the output absolute sound level with the input absolute sound level, a target sound level can be implemented as a listener intends. With this system introduced, sound source producers are able to focus on the completion of a sound source itself without an unnecessary competition for sound levels, and only by inputting the differential reduction tag, they can implement a sound level balance as intended. At the same time, listeners are able to appreciate all kinds of sound sources fit for the standard of absolute s ound levels they want to listen to, without a process of trial and error, no matter what kinds of listening environments and sound systems they have.

• Phonetics and Speech Sciences
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• v.3 no.3
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• pp.35-47
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• 2011

The purpose of this study is to examine the influence of Chinese high and level vs. rising tone on the pitch pattern of corresponding Sino-Korean words delivered by Chinese learners of Korean and to examine the aspects how these two tones of corresponding Chinese words affect the pitch patterns of Sino-Korean words. Scope of this research is limited to the Chinese learners of Korean, especially when they pronounce same-form-same-meaning Sino-Korean words. In this study, Chinese learners pronounced both Chinese words and corresponding Sino-Korean words. By using the software learners' pitch pattern were recorded, analyzed, and compared with the tone of corresponding Chinese words. Experimental results showed that Sino-Korean words were affected by Chinese 'high and level tone - high and level tone', 'high and level tone - rising tone', 'high and level tone - falling-rising tone', 'high and level tone - falling tone' and 'rising tone - falling tone' when they started with lenis sounds. On the other hand when Sino-Korean words started with aspirated sounds they were affected by Chinese 'rising tone - high and level tone', 'rising tone - rising tone', 'rising tone - falling-rising tone', 'rising tone - falling tone'. In conclusion, the Chinese learners' pitch patterns of Sino-Korean words are affected by both Chinese high and level & rising tone, especially when Sino-Korean words started with lenis sounds they were more affected by Chinese high and level tone, on the other hand Chinese rising tone influence Sino-Korean words more when they were started with aspirated sounds.