• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.166-171
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• 2012

In this paper, short-range underwater wireless communication technique using visible LEDs is proposed. As an alternative to conventional acoustic system, visible LED communications show high quality and high speed data transmission characteristics. We design a frequency modulation-based optical wireless audio transmission system. The CD4046B phase-locked loop device is applied to implement the frequency modulation and demodulation. With a transmission modulation of 100 kHz, audio signal has successfully received at a transmission distance of 30 cm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.189-197
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• 2011

OFDM systems are much studied for the recent high speed wireless optical communication system. OFDM system has basically high PAPR and ICI easily generated because of non-linearity and RF impairments. In the wireless optical communication system, optical output power driven by current of LED is not linear so that transmission signals are distorted. Therefore, research about reception performance of this nonlinear optical output emitted by non-linear LED transfer function and OFDM signal has been conducted. Nonlinear effect of LED is different from nonlinear effect of OFDM system in the conventional radio communication system, which degrades the BER performance. In this paper, we apply non-linear transfer function of recently studied LED into OFDM system. So, for reducing the PAPR and suppressing the ICI in frequency domain of receiver, we suggest a new PAPR reduction technique to reduce non-linear distortion of LED and an adaptive ICI suppression algorithm so that BER performance may be improved. Also, the proposed method is verified through simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1A
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• pp.8-18
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• 2011

Visible light communication (VLC) using optical sources which can be simultaneously utilized for illumination and communication is currently an attractive option for wireless personal area network. Improving the data rate in optical wireless communication system is challenging due to the limited bandwidth of the optical sources. In this paper, we design the singular value decomposition (SVD)-based multiplexing multi-input multi-output (MIMO) system to support two data streams in optical wireless channels. In order to improve the spectral efficiency, the rate adaptation using multi-level pulse amplitude modulation (PAM) is applied according to the channel condition and we propose the method to allocate the optical power, the offset and the size of modulation scheme theoretically under the constraints of the nonnegativity of the modulated signals, the aggregate optical power and the bit error rate (BER) requirement. The simulation results show that the proposed allocation method gives the better performance than the method to allocate the optical power equally for each data stream.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1595-1600
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• 2011

We analyzed the noise effect from artificial light and sunlight on the signal performance in visible light communication systems based on Intensity Modulation/Direct Detection(IM/DD). System performance was experimentally demonstrated by transmitting 50ksysmbol/s QPSK signals at 2MHz sub-carrier. And received signals were analyzed using EVM and RF spectrum. Finally, the system performance was improved by utilizing a visor and we confirm that the outdoor visible light communication was possible using IM/DD method.

• Journal of Advanced Navigation Technology
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• v.23 no.1
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• pp.61-68
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• 2019

Underwater wireless light communication system is quite necessary to retrieve recorded data from underwater devices or the black box without taking back it body. In this paper, a research on the light sensor technology in underwater wireless light communication under turbid sea was studied. A noise source under turbid sea for light communication was analysed, and a sensor system for light sensing using the reference light signal to remove the noises and to improve the output swing power wasstudied. Also, an underwater communication system was manufactured to validate the good performance of the development system, and using the system, the good performance of the developed system was validated through the light communication test in the tank containing the turbid sea water was presented.

• TTA Journal
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• s.126
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• pp.69-72
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• 2009

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.288-290
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• 2001

서로 인접한 두 개의 무선광통신 빔에서 발생하는 혼신을 소거하기 위하여 수신부에 편광기를 사용하였다. 광원측에서는 두 개의 레이저다이오드의 편파가 서로 수직하도록 설치하고 수신부에서는 각각의 편파에 일치하도록 편광기를 설치한 자동정렬형 광검출기를 구성하였다. 수신부의 포토다이오드는 각각의 편파에 일치하는 빔의 최대점을 찾아서 자동적으로 정렬한다. 두 개의 광원의 파장이 유사하여 광학적 필터로 혼신의 소거가 어려운 구간에서 이 구조를 사용하면 쉽게 혼신을 해소한다.

• Korean Journal of Optics and Photonics
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• v.31 no.6
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• pp.259-267
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• 2020

We evaluate the degradation of receiver sensitivity induced by direct and indirect exposure to solar irradiance in free-space optical communication systems. For this purpose, we calculate the variances of numerous noise components arising from solar irradiance, and then estimate the receiver sensitivity penalties for intensity-modulation/direct-detection and coherent systems. The results show that the penalties are less than 1.3 dB when indirect sunlight impinges on the detector, regardless of the system. However, the sensitivity penalties are estimated to be larger than 30 dB when the sunlight is directly incident upon the receiver. These penalties are barely reduced if we insert an optical polarizer, or if we adjust the bandwidth of an optical filter at the receiver to be as narrow as the signal's bandwidth.

• Electronics and Telecommunications Trends
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• v.19 no.6 s.90
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• pp.13-23
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• 2004

각종 대용량 디지털 멀티미디어 기기의 보급과 사용자 주변 환경의 네트워크화에 따라 고밀도 환경에서 고품질 광대역 무선 서비스를 제공할 수 있는 광무선 통신 기술이 유비쿼터스 네트워크를 실현할 유망기술로 부각되고 있다. 전파를 사용한 무선통신 방식에 비해 무한대에 가까운 대역폭과 보안성을 갖는 광무선 통신 기술의 특성과 기본 원리를 소개하고, 지금까지 개발된 기술 수준과 활용 현황 및 고성능광무선 통신 기술의 실용화를 위해 우선적으로 해결해야 할 기술적 과제들과 최근 연구개발 동향을 살펴본다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.4
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• pp.127-134
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• 2015

VLC(Visible Light Communication) is the technology to send and receive data by using visible light that LED emits. The basic principle of VLC is the communication by using flashing(ON/OFF) of the light from the LED that changes electricity to light in short time. As the recent advances in LED technology, VLC is also received a lot of attention and the research about it is in progress actively. Especially, the interest about indoor VLC system is increasing because the visible light can't pass through the wall. In this paper, we compose the indoor SISO VLC system with NRZ-OOK and VPPM modulation schemes. Also, we apply SR-ARQ, a kind of re-transmission error control schemes, to the VLC system. And then, we compare and analyze the performance of communication according to the location of receiver and the type of modulation by using BER, the number of transmission and throughput.