• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.2
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• pp.73-79
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• 2014

Visible light communication is a communication method using an LED having a high-speed ON / OFF rate data to be transmitted, it is used as a wireless high speed data transmission. VLC system evolves, the problem of basic research is intended to improve performance and ensure reliability of the communication. The nature of the visible light communication, communication is performed only in the reach of the light, which indicates a big difference by the emission angle of the light. Therefore, in this paper, in the case of indoor environments generally, with the attributes of the multiple LED is equipped, was applied to a MIMO (Multiple Input Multiple Output) communication system. and analyzed SNR performance and total power can be obtained on the reception side by changing the emission angle of the transmitter. As a result of the simulation was run against this, it was confirmed that there is a significant impact on the performance of BER and SNR performance by the emission angle of the transmitter.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.12
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• pp.1203-1209
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• 2011

In this paper, the degradation evaluation method of VLC (Visible Light Communication) wireless module after high dose rate gamma-ray irradiation using the thermal infrared camera is proposed. First, the heating characteristics of the active devices embedded in the VLC wireless module during the condition of normal operation is monitored by thermal infrared camera. By the image processing technique, the trends of the intensity of the heat emitted by the active devices are calculated and stored. The feature of the blob area including the area of the active devices in the thermal infrared image is extracted and stored. The feature used in this paper is the mean value of the gray levels in the blob area. The same VLC module has been gamma irradiated at the dose rate of about 4.0 kGy/h during 72 hours up to a total dose of 288 kGy. And then, the heating characteristics of the active devices embedded in the VLC wireless module after high dose gamma ray irradiation is observed by thermal infrared camera. The high dose gamma-ray induced degradation of the active devices embedded in the VLC module was evaluated by comparing the mean value of the blob area to the one of the same blob area of the VLC module before the gamma ray irradiation.

• ETRI Journal
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• v.37 no.4
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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.

• Journal of Convergence for Information Technology
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• v.10 no.2
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• pp.32-38
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• 2020

In this paper, we analyze the modulation scheme for high speed transmission in visible light communication system, and study non-orthogonal multiplexing, dimming level and transmission power ratio. Conventional visible light communication has a disadvantage in that it is difficult to multi-transmit to increase the transmission speed. Multi-transmission technique is necessary for high-speed transmission at the transmitter. Since general visible light communication has a limitation in multiple transmission, various researches for high-speed transmission have been conducted. In order to solve this problem, this paper proposes a multiple modulation scheme for high-speed visible light communication using non-orthogonal multiplex transmission scheme and a future research direction.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.459-465
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• 2014

Visible light communications (VLC) using the intensity modulation of light-emitting diodes (LEDs) provides a new communication medium to overcome the shortage of radio spectrum, and allows reuse of LED lighting infrastructures. Orthogonal frequency-division multiplexing (OFDM) was introduced to VLC for its merits in mitigating the fading effects resulting from delay spread, and in avoiding low-frequency ambient interference. Noise and clipping are two major factors that degrade the performance of OFDM in VLC. A larger signal easily overcomes noise, but experiences impairment by clipping. Therefore, degradation due to clipping has a trade-off relationship with that due to noise, depending on the signal amplitude of OFDM. In this paper, the optimal signal amplitude in the trade-off is obtained by simulation when the dimming and LED intensity are given. The former indicates a user's requirement for lighting, and the latter represents the channel quality. The required LED intensity-to-noise ratio, as the channel quality that guarantees dimming as well as an adequate bit-error rate (BER), is also discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1233-1239
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• 2011

The visible light convergence communication technology is suitable for indoor wireless communication and digital lighting fixtures, it could be used as lighting devices as well as a communication device. However, because that VLC is the technology of came to world a few years ago, there are many problems which had to solve. The signal sensing of VLC transmitter is one of the most challenging issue in VLC systems. Therefore in this paper, we analysis the performance of various sensing scheme for efficient detection of VLC systems. The signal of user is OFDM signal and the wirelss channel between a user and VLC system is modeled as indoor VLC channel. From the simulation results, it is confirmed that the proposed scheme is very effective to signal sensing for VLC systems.

• Journal of Digital Convergence
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• v.12 no.8
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• pp.249-255
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• 2014

In this paper, we proposed to reduce the interference in the visible light Communication with multi-LEDs for improving the performance of BER and satisfied the QoS. LED is not only lighting device, but also transmitting device in the VLC. Our proposed system is aim to decrease the interference in the multi-LEDs. In addition, it occurred the ISI and CCI by transmitter to receiver different distance. To solve this problem, we proposed the multi-LEDs system using walsh code to reduce ISI and CCI. In addition, our proposed system is able to improve the performance of BER and satisfied the Qos to desire users.

• Journal of Sensor Science and Technology
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• v.23 no.5
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• pp.349-355
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• 2014

In this paper, we developed a new method to transmit multiple visible light channels in time division mode using the AC power line frequency in order to prevent the crosstalk between adjacent optical signals. Synchronizing pulses are generated from the 220 V power line, and one pulse period is subdivided into several time slots for visible light channels. Each channel transmits data in a predefined time slot without interfering adjacent channels. In experiments, synchronizing pulses with a repetition rate of 240 Hz were generated from the 60 Hz power line, and three VLC channels with a bit rate of 9.6 kbps transmitted data independently using the time slots between synchronizing pulses. This configuration is very useful in constructing time division VLC networks for multiple sensors.

• Journal of Korea Multimedia Society
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• v.22 no.2
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• pp.186-193
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• 2019

Visible light communication technology is being studied and developed in various ways due to advantages such as high transmission speed, excellent positioning and higher security. However, existing visible light communication systems have difficulties in entering the market because they use special transmitters and receivers. We will overcome the difficulty if we develope a VLC system that uses a conventional LED light as a transmitter and a smartphone camera as a receiver. What matters is that LED lights include a scatter filter to prevent glareness for human eyes, but the existing VLC(Visual Light Communication) method can not be applied. In this paper, we propose a method to encode data with On / Off patterns of LEDs in the lighting with $M{\times}N$ LEDs. We defined parameters like L-off-able and K-seperated to facilitate the recognition of On / Off patterns in the diffused Lights. We conducted experiments using an LED lighting and smart phones to determine the parameter values. Also, the maximum transmission rate of our encoding technique is mathematically presented. Our encoding scheme can be applied to indoor and outdoor positioning applications or settlement of commercial transactions.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.1
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• pp.76-79
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• 2015

Visible light communication (VLC) is a short range optical communication technology using light emitting diodes. In this paper, we implement variable pulse position modulation (VPPM) defined in the IEEE 802.15.7 standard with a Cortex-M processor, which is a new modulation scheme for VLC providing a dimming control mechanism for flicker-free optical communication. The synchronization procedure between the transmitter and receiver is not defined clearly in the VPPM standard. In order to synchronize the transmitter and receiver easily, two overhead bits are used including one start bit and one stop bit modulated by on-off keying (OOK). Experimental results under various environmental conditions show that the proposed VPPM can support a seamless 100 Kbps data rate with 10 levels in the dimming control.