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Modulations for Visible Light Communications With Dimming Control
Kwonhyung Lee,Hyuncheol Park IEEE 2011 IEEE photonics technology letters Vol.23 No.16
<P>Visible light communication (VLC) uses solid-state lightings to transmit information; therefore, it is necessary that modulation schemes for VLC provide dimming control. In this letter, we propose a multiple pulse position modulation (MPPM) to offer both functions of modulating data-stream and controlling the brightness at the same time. According to the dimming level, we control the number of pulses of MPPM in one symbol duration. We analyze communication performance in terms of the normalized power requirement and spectral efficiency. From our studies, we show that MPPM is superior to variable on-off keying (VOOK) and variable pulse position modulation (VPPM) proposed in the IEEE 802.15 VLC task group.</P>
Indoor Channel Characteristics for Visible Light Communications
Kwonhyung Lee,Hyuncheol Park,Barry, J R IEEE 2011 IEEE communications letters Vol.15 No.2
<P>In this letter, we present indoor multipath dispersion characteristics for visible light communications (VLC). Since the VLC uses a wide spectrum between 380 nm and 780 nm, the conventional narrowband model for infrared may not apply. We generalize the Barry's model by including wavelength-dependent white LED characteristics and spectral reflectance of indoor reflectors. We perform a computer simulation to compare the power delay profile of the VLC with that of infrared communications. From our studies, we show that the VLC provides a larger transmission bandwidth than infrared communications.</P>
Multi-user Chaotic UWB System for Wireless Connectivity Applications
Mi-Hyun Son,Kwonhyung Lee,Jaehyon Kim,Sang-Min Han,Hyuncheol Park 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this paper, the chaotic Ultra-wideband (UWB) system is described for multi-user wireless connectivity applications. A simple architecture is designed by using a chaotic UWB signal and a noncoherent detection scheme. We use the prime sequence code based on chaotic on-off keying (PSC?COOK) in an asynchronous transmission channel for a simultaneously operating piconets environment. Moreover, the suggested adaptive decision algorithm enables to recover the variance of received power due to change in the communication distance. The performance of prime sequence code based COOK system is simulated by computer simulations. The proposed system guarantees three users in a single band 500㎒ without degradation in performance.
권상석(Sangseok Kweon),이권형(Kwonhyung Lee) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
Nowadays, vehicles are essential to reduce carbon dioxide and improve fuel economy according to environmental regulations. Thereby vehicle companies are under researches on lightweight vehicle. Reducing weight of suspension system was difficult matter because suspension system is key security parts in the vehicle. A knuckle of the suspension system is a key part which has a great influence on vehicle’s steer ability and stability. For this reason, strength and durability must be considered as important matters during development of the knuckle. So it mainly made from steel. But production of aluminum knuckle has become possible due to the development of high strength aluminum alloy and manufacturing processes. The aluminum knuckle’s weight is lighter than a steel knuckle but other performances such as strength, vibration characteristics and clearance between related parts could be worse. So that must be carefully considered during the product development. In this study, CAE was used for structural design optimization. It helped the development of aluminum knuckle with reducing trial and error and solving predicted problems in advance. Structural analysis of aluminum knuckle was optimized by comparison of the steel knuckle with the aluminum knuckle. The optimized aluminum knuckle by structural analysis was checked on durability test and modal test. Aluminum knuckle has achieved lightweight and improved on natural frequency. Also the aluminum knuckle has confirmed equivalent durability with the steel knuckle.