• 융합정보논문지
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• 제11권2호
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• pp.25-30
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• 2021

본 논문에서는 가시광 통신시스템에서 플리커 완화 및 BER 성능 향상을 위한 코딩 기법에 관해서 연구하였다. 가시광 통신의 전송 속도를 높이기 위해 다수의 LED를 사용하는 멀티전송 다중 LED 전송시스템이 활발히 연구되고 있다. 그러나 N개의 LED를 사용하는 다중 LED 가시광 통신시스템에서 N개의 LED를 통해 데이터를 전송할 때, 데이터 시퀀스에 따라 동시에 0이 전송되는 연집 Zero 구간이 발생하고, 또한 1의 전송 구간이 서로 다르기 때문에 플리커 현상과 Dimming level의 변화로 인한 조명 성능 저하 현상이 발생하게 된다. 가시광 통신시스템은 통신 및 조명 기능을 동시에 수행하는 통신시스템이다. 따라서 통신의 전송 효율과 조명의 밝기를 동시에 고려되어야 한다. 우리는 이러한 문제를 해결하기 위해 각각의 LED 데이터 시퀀스의 코딩 맵핑을 통해 플리커 현상과 Dimming level 문제를 완화하고 에러 검출 및 BER 성능을 향상시킬 수 있는 플리커 완화 기법을 제안하였다.

• 조명전기설비학회논문지
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• 제21권10호
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• pp.150-158
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• 2007

규모가 큰 제철소는 전기로를 포함한 시간에 따라 변하는 비선형 부하를 가지고 있다. 이들 비선형 부하는 고조파 전류를 발생시키고, 전력계통의 전압을 왜곡시킨다. 플리커는 전압 변동의 크기에 따라 램프의 방출 변화에 의한 인간의 지각 효과로 정의된다. SVC의 주 목적은 공통결합점에서 전압을 한계값 이하로 유지하는데 있다. 본 논문에서는 SVC 투입 전후의 고조파와 플리커 저감 효과를 분석하고, IEC 61000-3-6과 IEC 61000-3-7에 의해 평가하였다.

• Journal of Electrical Engineering and Technology
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• 제3권3호
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• pp.314-319
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• 2008

Power quality simulation plays an important role in many practical cases, for example, when deciding the capacity of the related mitigation devices, assessing the influence of installing a nonlinear load in the distribution part, dissolving the quality issues between utilities and customers, and so on. For these purposes, many dedicated tools have been used in order to assess the level of quality distortions by various kinds of PQ indices. However, there are few modules that can accurately simulate the flicker phenomenon, that is, $P_{st}$ and the nonlinear and chaotic behavior of the electrical arc furnace, which is one of the representative nonlinear loads. This paper deals with the useful and simple modules for the voltage flicker simulation in the distribution and transmission level under the environment of Matlab/Simulink. With these modules, the various conditions of distribution systems and the capacities of arc furnaces with the chaotic characteristic can be easily taken into account.

• ETRI Journal
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• 제37권4호
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• pp.677-684
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• 2015

Recently, orthogonal frequency-division multiplexing (OFDM) was applied to VLC systems owing to its high rate capability. On the other hand, a real-valued unipolar OFDM signal for VLC significantly reduces bandwidth efficiency. For practical implementation, channel estimation is required for data demodulation, which causes a further decrease in spectral efficiency. In addition, the large fluctuation of an OFDM signal results in poor illumination quality, such as chromaticity changes. This paper proposes a spectrally efficient method based on a hidden-pilot-aided precoding technology for VLC with less flickering than a conventional OFDM-based method. This approach can obtain channel information without any loss of bandwidth efficiency while ensuring illumination quality by reducing the flickering effect of an OFDM-based VLC. The simulation results show that the proposed method provides a 6.4% gain in bandwidth efficiency with a 4% reduction in flicker compared to a conventional OFDM-based method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 F
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• pp.2076-2078
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• 1998

This paper presents STATCON(Static Condenser) control schemes for voltage regulation, power factor correction and harmonics mitigation. Each control scheme can be applied in the system depending on the system requirements. The 20KVA STATCON is developed and tested in the reduced system model for the verification of three different control algorithms. The results of proposed controls are compared for power factor correction and voltage regulation algorithms. For each algorithm, harmonic mitigation scheme is adopted as a part of control. Finally verification of STATCON for the transient response is implemented by voltage flicker test.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권4호
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• pp.1276-1291
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• 2014

In the field of visible light communication (VLC), light-emitting diodes (LEDs) are used for transmitting data via visible light. In this study, we analyze pulse dual slope modulation (PDSM) as a means of delivering information in VLC. PDSM involves the modulation of symmetrical slope pulses to encode binary 0s and 1s, and owing to the moderately increasing and decreasing pulse shapes that are created, this method enables more spectral efficiency than the variable pulse position modulation (VPPM) technique currently adopted in IEEE 802.15.7. In particular, PDSM allows for the avoidance of intra-frame flicker by providing idle pulses in a spectrum-efficient way. A simple detection scheme is proposed for PDSMsignals, and its bit error rate (BER) is analyzed mathematically at varying slopes to validate the process through simulation. The BER performance of PDSM detection using dual sampling is compared to the performances of PDSM and VPPM using correlation detection. It is found that, when the probability of idle pulse transmission is less than 0.08 and higher than 0, the BER of dual sampling PDSM is lower than that of PDSM using correlation detection over the entire light intensity range.

• Current Optics and Photonics
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• 제2권5호
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• pp.422-430
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• 2018

Rolling shutter operation of CMOS cameras can be utilized in optical camera communications in order to transmit data from an LED to mobile devices such as smart-phones. From temporally modulated light, a spatial flicker pattern is obtained in the captured image, and this is used for signal recovery. Due to the degradation of rolling shutter images caused by light smear, motion blur, and focus blur, the conventional decoding schemes for rolling shutter cameras based on the pattern width for 'OFF' and 'ON' cannot guarantee robust communications performance for practical uses. Aside from conventional techniques, such as polynomial fitting, histogram equalization can be used for blurry light mitigation, but it requires additional computation abilities resulting in burdens on mobile devices. This paper proposes a transition-based decoding scheme for rolling shutter cameras in order to offer simple and robust data decoding in the presence of image degradation. Based on the designed synchronization pulse and modulated data symbols according to the LED dimming level, the decoding process is conducted by observing the transition patterns of two sequential symbol pulses. For this, the extended symbol pulse caused by consecutive symbol pulses with the same level determines whether the second pulse should be included for the next bit decoding or not. The proposed method simply identifies the transition patterns of sequential symbol pulses other than the pattern width of 'OFF' and 'ON' for data decoding, and thus, it is simpler and more accurate. Experimental results ensured that the transition-based decoding scheme is robust even in the presence of blurry lights in the captured image at various dimming levels