• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.11
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• pp.2043-2047
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• 2010

This study is to solve problems of depletion of RF bandwidth frequency, confusion possibility, security that current wireless communications system have and is to confirm possibility of applying next generation network. To solve problems of current wireless communications system, visible light communications system for power line communications using ATmega16 Microcontroller is was realized and receiver property was analyzed. PLC exclusive chip APLC-485MA, Microcontroller ATmega16, 5pi bulb type LED and high flux LED, visible light receiving sensor LLS08-A1 were used for transmitter and receiver. Performance was analyzed by designed program and an oscilloscope. It was showed average 20% improved receiver rate rather than bulb type LED in the case of high flux LED through voltage change rate on communication distance and LED type of distance between 10 to 50 cm. The blue LED showed the best performance among measured LED types with above 10% of voltage decreasing rate. But As it gradually becomes more distant, the precise date was difficult to obtain due to weak light. To overcome these sort of problems, specific values such as changing conditions and efficiency value relevant to light emitting parts and visible light receiving sensor should be calculated and continuous study and improvements should also be accomplished for the better communications condition.

• Journal of IKEEE
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• v.23 no.3
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• pp.1082-1087
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• 2019

In this study, ECG signal amplifier, wireless transmitter/receiver circuit, signal processing filter circuit and A/D converter circuit design required for the development of small sized ECG module for wireless transmission/ reception were performed. In order to verify the performance of ECG sensors, the measurement was performed from 1 m to 3 m to measure the signal noise ratio according to the gateway distance. Experimental results showed that the signal noise ratio at 2 m distance was 17.18 dB on average, which fulfilled the requirements for commercialization. The experimental results obtained in this study are expected to contribute to the low cost, high efficiency mobile health field where remote monitoring diagnosis can be applied to small biometric devices for chronic disease management.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.12
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• pp.907-914
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• 2018

Wireless charging has been actively researched and popularized owing to the potential convenience of being able to charge electronic devices without wires for users. However, the receiver on the wireless charging pad is not charged when the center of the receiver is misaligned; thus, the center of the receiver must be adjusted well. This misalignment may greatly reduce the convenience of wireless charging. To overcome this limitation of wireless charging, a coil is designed to improve the positional freedom of the receiver. The positional freedom of the Rx coil is improved when the outer diameter of Tx coil is larger than when Rx and Tx coils are almost the same size. When the Tx coil has a larger outer diameter than that of the Rx coil, the efficiency at the center is somewhat lowered, but the efficiency is improved compared to when the center is out of order. In this paper, a double coil structure having an outer and an inner coil is proposed. The double coil structure further improves the efficiency, compared with one coil with the same outer size. The simulation and measurement results demonstrated that the tendency was consistent, and it was verified that the degree of freedom of the Rx coil is improved by adding the inner coil, while the size of the outer coil was the same. The measurement shows that the transmission efficiency of the conventional Tx coil is 37 %, the larger outer diameter coil is 45 %, and double coil is 47 % when the distance of the Tx/Rx coil is 3 mm, the misalignment is 15 mm and current flowing in the Rx coil is 1 A at an operating frequency of 105 to 210 kHz.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06a
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• pp.359-360
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• 2011

In this work. a new receiver-driven channel rendezvous mechanism is proposed for multi-channel communication in Wireless sensor networks (WSNs). The work is a light-weight scheduled scheme. seems to be incurring less overhead in compare to traditional common control channel based rendezvous mechanisms.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.2059-2062
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• 2002

For detection of digitally modulated signals, the receiver must be provide with accurate carrier phase and symbol timing estimates. So far, tots of algorithms have been suggested for those purposes. In general, a interpolation filter with TED(Timing Error Detection) like Gardner algorithm is popularly used for symbol timing estimate of digital communication receiver. Apart from the performance point of view, a multiplicative operation of any interpolation filter limits the symbol rate of the system. Hence, we suggest a new symbol timing estimate algorithm for high speed burst-mode fixed wireless communication system and analyze its performance in the AWGN channel.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.588-600
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• 2017

We develop a wireless, contact free power transfer mechanism that is safer than the direct metallic contact and robust to imperfect alignment on landing at the base station. A magnetic field is created using inductors on both the transmitting and receiving sides. We use the inductive wireless recharging to increase autonomy and decrease the sensor interference by reducing the inductor loop size. By locating four independent small receiver loops and corresponding four circuits around the quadrotor UAV, we can increase safety from circuit malfunctions in comparison to the use of just one loop. On the base station, four folding robotic bars are used to realign the receiver loops over the transmitter loops. After adequate recharging as measured by battery voltages or power consumption at the bae station, the UAV sends a signal to the base station to open the robotic bars and takes off once freed from the robotic bars.

• Journal of information and communication convergence engineering
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• v.17 no.3
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• pp.221-226
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• 2019

In this work, a transmitter/receiver front-end module (T/R FEM) with an automatic Tx/Rx switching scheme for a 2.4 GHz microwave power transfer is developed for a retro-reflective beamforming scheme. Recently, research on wireless power transfer techniques has moved to wireless charging systems for mobile devices. Retro-reflective beamforming is a good candidate for tracking the spatial position of a mobile device to be charged. In Tx mode, the T/R FEM generates a minimum of 1 W. It also comprises an amplitude and phase monitoring port for transmitting RF power. In Rx mode, it passes an Rx pilot signal from a mobile device to a digital baseband subsystem to recognize the position of the mobile device. The insertion loss of the Rx signal path is 4.5 dB. The Tx and Rx modes are automatically switched by detecting the Tx input power. This T/R FEM is a design example of T/R FEMs for wireless charging systems based on a retro-reflective beamforming scheme.

• Progress in Superconductivity and Cryogenics
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• v.17 no.1
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• pp.36-39
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• 2015

Many studies are being conducted to implement wireless charging, for example, for cellular phones or electronic tooth brushes, via wireless power transmission technique. However, the magnetic induction method had a very short transmission distance. To solve this problem, the team of Professor Marin Soljacic proposed a magnetic resonance system that used two resonance coils with the same resonance frequency. It had an approximately 40% efficiency at a 2m distance. The system improved the low efficiency and short distance problems of the existing systems. So it could also widen the application range of wireless power transmission. Many studies on the subject are underway. In this paper, the superconductor coil was used to improve the efficiency of magnetic resonance wireless power transmission. The resonance wireless power transmission system had a source coil, a load coil, and resonance coils (a transmitter and a receiver). The efficiency and distance depended on the characteristics of the transmitter and receiver coils that had the same resonance frequency. Therefore, two resonance coils were fabricated by superconductors. The current density of the superconductor was higher than that of the normal conductor coil. Accordingly, it had a high quality-factor and improved efficiency.

• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.156-158
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• 2006

A super-regenerative receiver is designed and tested at 433 MHz ISM band, The designed receiver has the data rate of up to 200 kbps and a power consumption of 10 mW. We carried out the system performance test for the TX power of 0.1 mW and 1 m distance. The result of the bit-error rate test shows one bit error among the 4000 bits.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.12
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• pp.873-875
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• 2014

In this paper we describe an asynchronous MAC protocol with receiver-initiated duty cycling for energy-efficiency in wireless sensor networks(WSN). Legacy asynchronous MAC protocols, X-MAC and PW-MAC, has weaknesses which generates too many control packets and has data collision problem between multiple transmitters, respectively. Therefore, we propose a receiver-initiated asynchronous MAC protocol which generates control packets from transmitter to complement these disadvantages. Compared to the prior asynchronous duty cycling approaches of X-MAC and PW-MAC, the proposed protocol shows a improvement in energy-efficiency, throughput and latency from simulation results.