• 센서학회지
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• 제30권2호
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• pp.99-104
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• 2021

In this study, we utilized the duty factor of the transition frequency modulation (TFM) for the illumination control of the light emitting diode (LED) light in visible light communication (VLC). The average optical power is linearly proportional to the duty factor in TFM waveforms. We used the transition frequencies of Na=5 and Nb=1 for the high and the low bits, respectively, of the non-return-to-zero (NRZ) data in the VLC transmitter. A resistor and capacitor high-pass filter (HPF) was used in the VLC receiver to eliminate the 120 Hz optical noise from adjacent lighting lamps and the spikes at the HPF output were used to recover NRZ data from the TFM waveform. In experiments, the illumination of the LED light was controlled in the range of 25-90% of the constant-wave optical power by changing the duty factor of the TFM waveforms.

• 한국통신학회논문지
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• 제36권9B호
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• pp.1117-1125
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• 2011

이 논문에서는 LED(Light Emitting Diode) 조명을 이용한 간편한 가시광 통신 시스템을 구현하기 위해, 비 캐리어 NRZ-OOK(non-return to zero on off keying) 변조 방식을 사용하고, 가시광 송신을 위한 발광소자인 $3{\times}3$ 백색 LED 배열과 가시광 수신을 위한 여러 가지 포토다이오드를 사용하여 송수신 소자사이의 거리가 약 2.5m이고, 전체 시스템 속도가 115.2kbps의 전송속도를 가지는 가시광 시스템을 설계하여 구현 한다. 구현된 시스템의 성능분석을 위해 LED 와 포토다이오드 종류, LED 배열 수, 전송속도 따른 최대 송수신 거리를 구하고 여러 가지 구현시스템의 성능을 실험을 통해 분석한다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1418-1421
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• 2009

A series of new light-emitting random copolymers with fully conjugated structure was prepared, for the first time through the well-known Gilch polymerization between 1,4-bis(chloromethyl)-2-ethylhexyloxy-5-methoxybenzene and 2,5-bis(bromomethyl)thiophene monomers in different ratios. The synthesized polymers (on thin film) showed the maximum wavelength of UV-visible absorbance and photoluminescence (PL) near 500 nm and near 600 nm, respectively. A single-layer light-emitting diode device, which has a simple ITO (indium-tin oxide)/polymer/Al configuration, was fabricated by spin-coating of polymers and then vacuum evaporation of Al metal. The threshold bias of PMEHPVTVs was in the range of 3.5-10 V. As in the PL spectra, the maximum wavelength of light emission near 600 nm was also shown in electroluminescence (EL) spectra of PMEHPVTVs when the operating voltage was about 7 - 14 V.

• 센서학회지
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• 제25권2호
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• pp.131-137
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• 2016

In this study, a multilevel visible light communication (VLC) system based on resistor ladder circuit is designed to transmit medical data. VLC technology is being considered as an alternative wireless communication due to various advantages such as ubiquity, license free operation, low energy consumption, and no radio frequency (RF) radiation characteristics. With VLC even in places where traditional RF communication (e.g., Wi-Fi) is forbidden, significant bio-medical signal including the electrocardiography (ECG) and photoplethysmography (PPG) data can be transmitted. More lives could be saved anywhere by this potential advantage of VLC with a fast emergency response time. A multilevel transmission scheme is adopted to improve the data capacity with keeping simplicity, where data transmission rate can increase by log2m times (m is the number of voltage levels) than that of conventional VLC transmission based on on/off keying. In order to generate multi-amplitudes, resistor ladder circuit, which is a basic principle of digital to analog convertor, is employed, and information is transferred through LED (Light-Emitting Diode) with different voltage level. In the receiver side, multilevel signal is detected by optical receiver including a photo diode. Then, the collected data are analyzed to serve the necessary medical care to the concerned patient.

• 한국정보통신학회논문지
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• 제22권1호
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• pp.140-146
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• 2018

최근 실내조명으로 사용하는 LED(Light Emitting Diode)와 무선통신 기술을 융합한 가시광통신이 주목받고 있다. 하지만 가시광 통신은 광 신호를 측정할 수 있는 커버리지 내에서만 통신이 가능하고, 비가시선 영역에서 통신이 단절되는 현상이 발생한다. 본 논문에서는 가시광 통신의 커버리지 확장과 비가시선 영역에서 통신 단절 현상 개선을 위해 VLC(Visible Light Communication) 릴레이 모듈을 제안한다. 제안하는 VLC 릴레이 모듈은 송신기로부터 전달받은 패킷을 VLC 릴레이 모듈 및 수신기로 전송한다. 1개의 VLC 송신기와 3개의 VLC 릴레이 모듈을 설치하여 실험을 진행하였으며, VLC 릴레이 모듈의 증가에 따른 통신 커버리지 확장과 비가시선 영역에서 통신 단절 현상 개선을 확인하였다. 또한, 이중 샘플링 기법을 사용하여 광 신호 측정 성능이 2.4배 향상됨을 확인하였다.

• ETRI Journal
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• 제35권5호
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• pp.927-930
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• 2013

We propose a visible light communication system in which the color and brightness are controllable. Pulse width modulation and variable pulse position modulation (VPPM) schemes are used to control the color and brightness, respectively. A digital algorithm to decode VPPM signals is suggested and implemented. A seamless transmission is observed in a testbed experiment under various environmental conditions. The proposed scheme can be applied to emotional-lighting-based wireless optical communication.

• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.169-174
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• 2014

This paper proposes a novel beehive-shaped reflector for application to light-emitting diode (LED) transceivers for illumination and bi-directional visible light communication (VLC). By using a diffuse propagation model extended to line-of-sight and direct signals, the distribution of illuminance and the path loss of the transceiver are investigated to evaluate the performance of the beehive-shaped reflector. To verify bi-directional communication, a VLC-based image capture system, comprising a complementary metal-oxide semiconductor (CMOS) image sensor and video processor unit, is demonstrated. Real-time images captured by the CMOS camera are successfully transmitted to the monitoring system via a free-space channel at a rate of 115.2 kbps.

• Current Optics and Photonics
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• 제1권2호
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• pp.90-94
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• 2017

Visible light identification (VLID) is a user identification system for a door lock application using smartphone that adopts visible light communication (VLC) technology with the objective of high security, small form factor, and cost effectiveness. The user is verified by the identification application program of a smartphone via fingerprint recognition or password entry. If the authentication succeeds, the corresponding encoded visible light signals are transmitted by a light emitting diode (LED) camera flash. Then, only a small size and low cost photodiode as an outdoor interface converts the light signal to the digital data along with a comparator, and runs the authentication process, and releases the lock. VLID can utilize powerful state-of-the-art hardware and software of smartphones. Furthermore, the door lock system is allowed to be easily upgraded with advanced technologies without its modification and replacement. It can be upgraded by just update the software of smartphone application or replacing the smartphone with the latest one. Additionally, wireless connection between a smartphone and a smart home hub is established automatically via Bluetooth for updating the password and controlling the home devices. In this paper, we demonstrate a prototype VLID door lock system that is built up with LEGO blocks, a photodiode, a comparator circuit, Bluetooth module, and FPGA board.

• Journal of Advanced Marine Engineering and Technology
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• 제29권7호
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• pp.795-800
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• 2005

The optical properties of $ZnS_{y}Se_{1-x-y}:Te_x\;(x\;<\;0.08,\;y\∼0.11$) alloys grown by molecular beam epitaxy (MBE) have been investigated by photoluminescence (PL) and PL-excitation (PLE) spectroscopy. Good optical properties and high crystal quality were established with lattice match condition to GaAs substrate. At room temperature, emission in the visible spectrum region from blue to green was obtained by varying the Te content of the ZnSSe:Te alloy. The efficient blue and green emission were assigned to $Te_{1}$Tel and $Te_{n}$ (n$\geq$2) cluster bound excitons, respectively. Bright blue (462 nm) and green (535 nm) light emitting diodes (LEDs) have been developed using ZnSSe:Te system as an active layer.

• 한국정보전자통신기술학회논문지
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• 제6권1호
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• pp.51-56
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• 2013

본 논문에서는 LED 조명을 기반으로 미디어 전송기법 가시광통신 시스템 모듈 설계 및 효율 연구와 성능분석을 하였다. 고휘도 Withe LED조명을 이용한 가시광통신(Visible Light Communication) 송 수신기 모듈을 통해 미디어 전송 시스템을 구현하기 위해 송신부에는 1~12개의 LED 발광 소자와 수신부에는 PD(Photo Diode)센서를 구성하여 전송속도에 따른 최대 송 수신의 통신 거리를 실험해 보고자 가시광통신 시스템을 제안하였다. 또한 미디어 전송 시스템의 효율을 증대시키기 위해 LED모듈에 렌즈 착용시와 미착용시 각각의 성능을 측정하여 약 20%의 효율이 증가하였음을 확인 할 수 있었다.