• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.959-966
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• 2015

In this paper, we propose an indoor visible light communication(VLC) localization using Walsh code which can identify overlapped signals transmitted from the different LED sources as each of orthogonal signal at a receiver and using Manchester code which can eliminate the flicker of LED light and maintain a constant brightness. The proposed system can estimate the relative position of the receiver by using Lambertian radiation properties and trilateration method that are applied to the location information of fixed LED sources and the received signals from them. In order to verify the feasibility of the proposed system, we carried out the simulation in an indoor space with $6{\times}6{\times}1.5m^3$ installed LED lamps of 16. The simulation result shows that the proposed method achieves an average positioning error of 0.0536 m and a maximum positioning error of 0.2977 m.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.8
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• pp.1773-1779
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• 2015

Shore-to-sea visible light communication using color clustered multiple-input and multiple-output (MIMO) is presented. The proposed maritime visible light communication (MVLC) offers a low-cost, high-speed wireless link for shore-to-sea maritime communications. Each color cluster is comprised of 50 red, green and blue (RGB) light emitting diodes (LEDs) and is modulated using on-off-keying (OOK). Selection combining is performed at the receiver, producing diversity effect within that color cluster. In this paper, we employ sea states (wave height, wind speed, etc.) data from both Pierson-Moskowitz and JONSWAP spectrum models under atmospheric turbulence conditions. Based on the simulation model, the maritime link quality is analysed in terms of coverage distance and bit error rate performance. The results show that the proposed system provides an efficient MVLC, while satisfying International Association of Lighthouse Authorities (IALA) requirements for maritime buoyage system and also offering sufficient illumination from high power LEDs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.262-271
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• 2004

There are channel errors when video data are transmitted between encoder and decoder. These channel errors would make decoded image incorrect, so it is very important to detect and recover channel errors. This paper proposes a method of error detection and recovery by hiding specific information into video bitstream using fragile watermark and checking it later. The proposed method requires no additional bits into compressed bitstream since it embeds a user-specific data pattern in the least significant bits of LEVELs in VLC codewords. The decoder can extract the information to check whether the received bitstream has an error or not. We also propose to use this method to embed essential data such as motion vectors that can be used for error recovery. The proposed method can detect corrupted MBs that usually escape the conventional syntax-based error detection scheme. This proposed method is quite simple and of low complexity. So the method can be applied to multimedia communication system in low bitrate wireless channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.889-891
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• 2017

Visible light communication technology, which is a communication using LED lighting, is defined by IEEE 802.15.7 WG and active research is under way. Visible light communication is advantageous not only to avoid interference with existing RF communication but also to provide location based service through accurate positioning by utilizing LOS (Line of Sight) characteristic. Therefore, it is very easy and efficient to locate and track the user's location. In this paper, we implemented a visible light communication transceiver using USB interface for easy application to portable devices. It supports the mobility of mobile devices through internet protocol and showed BER performance of less than $10^{-3}dBm$ at over 1m, which is the height of lighting and smart device during walking.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.480-483
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• 2018

In this paper, we study the interference canceling and image sensing processing technology of multiple light sources for high speed transmission in CMOS sensor based visible light communication system. To improve transmission capacity in optical camera communications via image sensors, different data must be transmitted simultaneously from each LED. However, multiple LED light source environments for high-speed transmission can cause interference between adjacent LEDs. In this case, since the visible light communication system generally uses intensity modulation, when a plurality of LEDs transmit data at the same time, it is difficult to accurately detect the respective LEDs due to the light scattering interference of the adjacent LEDs. In order to solve this problem, the ON / OFF state of many LEDs of the light source is accurately recognized by using a dual CMOS sensor, and the spectral estimation technique and the pixel image signal processing technique of each LED are proposed. This technique can accurately recognize multiple LED pixels and improve the total average bit error rate and throughput of a MISO-VLC system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.6
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• pp.476-481
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• 2014

In this paper, we design the pre-equalizer of transmitter circuit in order to enhancement modulation bandwidth of white LED which is light source of VLC (Visible Light Communication). Also, we eliminate yellow light component by optical filtering which mitigate frequency response of white LED. Power loss by optical filtering is overcome by using convex lens. By applying proposed system, 3 dB bandwidth deciding modulation bandwidth of white LED increases from 3 MHz to more than 25 MHz and the transmission distance increases by optical design which secure additional signal power. We optically modulate NRZ-OOK signal to LED and receive light signal using APD. We analyze received data using CSA and RFSA. As a result, we experimently demonstrate the possibility that transmits NRZ-OOK signal up to 30 Mbps in 4.5 m, 50 Mbps in 1.5 m through the pre-equalizer and optical design.

• Restorative Dentistry and Endodontics
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• v.20 no.2
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• pp.721-731
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• 1995

The purpose of this study was to evaluate the adaptability to tooth structure of light-cured glass ionomer cements. In this, study, class V cavities were prepared on the buccal surfaces of thirty extracted human premolar teeth, and they were randomly assigned into 3 groups with 10 teeth. The cavities of each groups were filled with the Fuji II LC(GC International Corp., Japan), Vitremer(3M Dental Products Division, U.S.A) and VariGlass VLC(Caulk/Dentsply Inc., U.S.A.). The specimens were immersed in 1% methylene blue solution and stored in 100% realtive humidity at $37^{\circ}C$ for 5 days. And then, the specimens sectioned buccolingually. Degree of eke penetration at tooth--restoration interfaces were examined by magnifying glass at occlusal and gingival margin. The results were as follows : 1. On the occlusal margin, among the experimental groups, the group 2 showed the lowest microleakage($1.40{\pm}1.17$) and the group 1 showed the highest microleakage($3.10{\pm}0.99$). There was significant difference between group 1 and group 2(P<0.01). 2. On the gingival margin, among the experimental groups, the group 2 showed the lowest microleakage($2.50{\pm}1.08$) and the group 1 showed the highest microleakage($3.50{\pm}0.84$). But there was not significant. difference among the experimental groups(P>0.05). 3. The degree of microleakage at occlusal margin was less than gingival margin in all experimental groups.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1840-1846
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• 2014

An experimental outdoor optical wireless data communication system with an optical filter in the presence of sunlight or artificial light is presented. For the efficient blocking of light noise outdoors, we employ an optical filter made of microlouver film on the top of the photo diode. This filter is designed to block any light noise incident from an angle higher than $30^{\circ}$ on the assumption that light noise does not face the photo diode horizontally. Outdoor experiments daytime with the optical filtering have been conducted. The experimental results demonstrate that the optical filter effectively blocks nearly all light noise incident from the specified angle or higher and more than 90% of the transmitted data packets are successfully received. The proposed outdoor visible light data communication can thus facilitate a practical free space outdoor optical wireless data transmission.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.6296-6302
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• 2014

A new technique, which can increase the channel bandwidth in an optical wireless orthogonal frequency division multiplexing (OFDM) link based on a light emitting diode (LED), is proposed. The technique uses adaptive sampling to convert an OFDM signal to a sparse waveform. In compressive sensing (CS), a sparse signal that is sampled below the Nyquist/Shannon limit can be reconstructed successively with sufficient measurements. The data rate of the proposed CS-based visible light communication (VLC)-OFDM link increases from 30.72 Mb/s to 51.2 Mb/s showing an error vector magnitude (EVM) of 31 % at the quadrature phase shift keying (QPSK) symbol.

• Restorative Dentistry and Endodontics
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• v.18 no.1
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• pp.122-132
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• 1993

The aim of this study was to investigate the level of radiopacity of glass ionomer cements and to determine the optimum level of radiopacity that is the most compatible with the radiographic diagnosis of secondary caries. The experiments were performed in two parts. In the first part, the radiopacities of 9 glass ionomer cements (FI, FII, FI-LC, FII-LC, SI, SII, Vit, B-VLC, AC) and base materials(Ultra-Blend, Zinc phoaphate cements, Cavitec, Dycal) were measured by densitometer. Then all experimental materials were divided into 5 groups based on the level of radiopacity of enamel and dentin. In the second part, class III cavities with or without secondary caries were prepared in extracted anterior teeth. The representative materials of each group with different radiopacities were inserted into each cavity. The radiographs were interpreted by 15 dentists and seconsary caries were diagnosed according to a five-point confidence rating. Sensitivity and ROC analysis were used to compare observer performance. The following results were obtained : 1. The radipacity of glass ionomer cements varied between 1.111mm Al and 6.011mm Al equivalent. 2. Among experimental materials, three materials in group I had lower radiopacity than that of dentin. The radiopacity of two materials in group II slightly exeeded that of dentin. Three materials in group III had slightly lower radiopacity than that on enamel. The radiopacity of one material in group W was slightly higher than that of enamel. Four materals in group V had the radiopacity that exeeded over 2.0mm AI equivalent to that of enamel. 3. The group IV was the highest for sensitivity and the group V was the highest for ROC area. However, no significant differences were obtained among group II, III, IV and V (P<0.05) but only group I was significantly lower(P<0.01). 4. In comparison with the observer performance for the radiographic diagnosis of secondary caries, the group II, III, IV, and V were superior to the group I (P<0.01). And so the optimum level of radiopacity to detect the secondary caries was the radiopacity that is higher than that of dentin.