• 한국정보통신설비학회:학술대회논문집
• /
• 2008.08a
• /
• pp.7-11
• /
• 2008

Future electric lights will be composed of white LEDs (Light Emitting Diodes). Indoor wireless optical communication systems utilizing white LED lights have been studying about it. Generally, plural lights are installed in room. Therefore, their optical path difference must be considered. In this paper, the influence of an optical path difference has been investigated and two approaches against this problem are introduced. One uses OOK-RZ (On-Off Keying, Return-to-Zero) coding and the other uses optical OFDM (Orthogonal Frequency Division Multiplexing). From the results of computer simulations, we have found that these approaches are feasible for the wireless optical communication systems utilizing white LED lights.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.11 no.5
• /
• pp.608-614
• /
• 2018

In addition to the diffusion of ICT technology, various protocols of short range wireless communication technology are being applied for efficient information operation. However, due to limitations of short-range wireless communication, communication is not smooth in places where frequency environment is poor, such as frequency confusion and warehouse type factory. When an alternative is needed. The development of LED technology and expansion of infrastructure through LED based visible light communication is attracting attention as an alternative and spreading the usage in wide range now a days. In addition, the infrastructure has been expanded with solar panels in response to the development of smarthome built-in with renewable energy. In this situation, visible light communication using PD has been limitedly applied in a near environment where the receiving angle of the PD and the ambient light ensure the LoS and the influence of the ambient light is small. In order to solve this problem, we have implemented visible light communication using LED lighting with large current infrastructure and solar panel with large receiving area, and proposed a circuit for restoring accurate data even in ambient light. Through this study results, it is expected that visible light communication can be more widely used and this result used as the base data for visible light communication research using the solar panel as the receiver.

• Journal of the Optical Society of Korea
• /
• v.20 no.1
• /
• pp.36-41
• /
• 2016

Visible Light Communication (VLC) using Light Emitting Diodes (LEDs) within the existing lighting infrastructure can reduce the implementation cost and may gain higher throughput than radio frequency (RF) or Infrared (IR) based wireless systems. Current indoor VLC systems may suffer from poor downlink resource allocation problems and small system throughput. To address these two issues, we propose an algorithm called a conflict graph scheduling (CGS) algorithm, including a conflict graph and a scheme that is based on the conflict graph. The conflict graph can ensure that users are able to transmit data without interference. The scheme considers the user fairness and system throughput, so that they both can get optimum values. Simulation results show that the proposed algorithm can guarantee significant improvement of system throughput under the premise of fairness.

• Journal of Sensor Science and Technology
• /
• v.25 no.5
• /
• pp.303-309
• /
• 2016

In this paper, we introduce a new method for controlling the illumination of LEDs in visible light communication (VLC) by changing the duty cycle of Manchester code. When VLC data were transmitted in Manchester code, the average optical power of the LEDs was proportional to the duty cycle. In experiments, we controlled the illumination of a $3{\times}3$ LED array from 10% to 90% of its peak value by changing the duty cycle of the Manchester code. The synchronizing clocks required for encoding and decoding the Manchester code were supplied by pulse generators that were connected to a 220 V power line. All pulse generators made the same pulses with a repetition frequency of 120 Hz, and they were synchronized with the full-wave rectified voltage of the power line. This scheme is a very simple and useful method for constructing indoor wireless sensor networks using LED light.

• Journal of Sensor Science and Technology
• /
• v.24 no.3
• /
• pp.145-150
• /
• 2015

We introduce a new method of time-division visible light communication (VLC) using LED lamp light for the generation of synchronizing pulses. The LED lamp, driven by an AC 220-V power line, radiates light that has a 120-Hz frequency component. The pulse generator in each VLC system receives the LED lamp light and generates the synchronizing pulses that are required for time-division transmission of multiple VLC channels. The pulse period is subdivided into several time slots for VLC channels. In experiments, 120-Hz synchronizing pulses were generated using LED lamp light, and three VLC channels were transmitted independently without interfering with each other in a condition where the VLC signals overlapped in space. This configuration is useful in constructing multiple wireless sensor networks that are safe and without interference in locations where LED lamps are used for illumination.

• Current Optics and Photonics
• /
• v.2 no.4
• /
• pp.308-314
• /
• 2018

Visible light communication (VLC) is considered a strong future candidate for indoor wireless communication. However, its performance seems to be relatively unsatisfactory when compared to wireless local area network (WLAN) communication using millimeter waves. To improve the performance of VLC, numerous technologies have been proposed so far, in both electrical and optical domains. Among the proposals, optical beamforming (OB) is an optical-domain technology that can concentrate light in a specific direction or on a target spot. It can significantly improve VLC performance and can be widely used, because it does not depend on electrical modulation schemes. Therefore, this review discusses the concept, principle, and types of OB, the structure of a VLC system using OB, performance results of OB, and the combination of OB with electrical signal modulation in VLC. OB is expected to be one of the key techniques in future VLC implementations, similar to radio-frequency beamforming in millimeter-wave communication.

• Journal of information and communication convergence engineering
• /
• v.19 no.4
• /
• pp.269-275
• /
• 2021

Light-emitting diodes (LEDs) are modulated using a square wave pulse sequence for flicker prevention and dimming control in visible light communication (VLC). In a VLC transmitter, the high and low bits of the non-return-to-zero (NRZ) data are converted to two square waves of different frequencies, which continue for a finite time defined by the fill ratio in an NRZ bit time. As the average optical power was kept constant and independent of data transmission, the LED was flicker-free. Dimming control is carried out by changing the fill ratio of the square wave in the NRZ bit time. In the experiments, the illumination of the LED light was controlled in the range of approximately 19.2% to 96.2% of the continuous square wave modulated LED light. In the VLC receiver, a high-pass filter combined with a latch circuit was used to recover the transmitted signal while preventing noise interference from adjacent lighting lamps.

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

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.12
• /
• pp.1513-1519
• /
• 2013

A genetic algorithm (GA) is an optimization technique based on natural evolution theory to find the global optimal solution. Unlike the gradient-based method, it can design nanoscale structures in the electric field because it does not require sensitivity calculation. This research intends to design a nanoaperture with an unprecedented shape by the topology optimization scheme based on the GA and ON/OFF method in the visible frequency range. This research mainly aims to maximize the transmission rate at a measuring area located 10nm under the exit plane and to minimize the electric distribution at other locations. The finite element analysis (FEA) and optimization process are performed by using the commercial package COMSOL combined with the Matlab programming. The final results of the optimized model are analyzed by a comparison of the electric field intensity and the spot size of near field with those of the initial model.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.15 no.1
• /
• pp.5-11
• /
• 1978

Si-ZnSe n-n heterojunction was made by growing ZnSe thin film on the Si single crystal (111) surface with Bash evaporating method in vacuum. This heterojunction was found to be a useful device for frequency meter in the visible wave-length from the measuring of the photovoltaic effect of the heterojunction.