• Journal of Digital Convergence
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• v.17 no.9
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• pp.161-171
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• 2019

Government transactions over wireless electronic devices are not safe and hence the messages are prone to attack. Thereby, devices supporting wireless Internet must assure the same level of security and privacy as the wired network. National public key infrastructure (NPKI) for electronic government used in the wired environment is not suitable for wireless environment for mobile government (mGovernment) because of the limitations of computing power, memory capacity and restricted battery power. This requires the development of a new NPKI for mGovernment, denoted as mNPKI, to developing countries, which provides the same security level as the wired NPKI. For the wireless environment requirements, mNPKI is based on short lived certificates. Analysis shows that mNPKI is well suited to wireless Internet and provides the same security requirement from the wired NPKI.

• Journal of IKEEE
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• v.17 no.3
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• pp.317-323
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• 2013

In this paper, 25W wireless power transmission(WPT) system using the coupled magnetic resonance is presented. The WPT system consists of a 100W class-F power transmitter, 1.7MHz magnetic resonators and a 40W full-bridge receiver using diodes. Especially, the transmit power control function using the 400MHz FSK communication between the transmitter and the receiver is adopted in the proposed system for the stable power transmission. Using the system and the power control function, the WPT system can be adopted in the various electronic devices and the commercialization of WPT system can be moved forward.

• Journal of Industrial Convergence
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• v.18 no.2
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• pp.69-75
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• 2020

Industrial IoT has much interested in wireless mesh networks (WMNs) due to cost effectiveness and coverage. According to the advance in caching technology, WMNs have been researched to overcome the throughput degradation of multihop environment. However, there is few researches of cache power consumption models for WMNs. In particular, a wired line based cache power consumption model in content-centric networks is not still proper to WMNs. In this paper, we split the amount of cache power from the idle power consumption of CPU, and then the cache hit ratio proportional power consumption model (CHR-model) is proposed. The proposed CHR-model provides more accurate power consumption in WMNs, compared with the conventional cache power efficiency based consumption model (CPE-model). The proposed CHR-model can provide a reference model to improve energy-efficient cache operation for Industrial IoT.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1877-1884
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• 2014

Because of the limited power resource, we need a reliable low-power media access control technique suitable for unmaned remote sensor operation condition for the unmanned sensor processor to perform the task in the remote wireless network situation. Therefore CSMA/CA and X-MAC is generally considered to effectively transmit the signal in the low-power wireless network. In this paper, we propose the more efficient low-power LP-MAC Technique which consumes the minimum power and transmits the data faster in condition that the mobile nodes' joining to and leaving from the network which consists of the fixed nodes is fluid. The fixed nodes operate in an asynchronous mode to perform the network self-configuration and transmit data faster to the mobile node which is frequently join and leave the network. When the mobile node leaves the network, the network's operation mode will be synchronous mode to achieve the minimum power consumption, thus the minimum power operation becomes possible.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.11
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• pp.834-841
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• 2018

A power amplifier for subgigahertz short-range wireless communication using $0.18-{\mu}m$ CMOS technology is presented. It is designed as a differential structure to form easily a virtual ground node, to increase output power, and to design a cascode structure to prevent breakdown. The transistor gate width was determined to maximize the output power and power-added efficiency(PAE), and the balun was optimized through electromagnetic simulation to minimize the loss caused by the matching network. This power amplifier had a gain of more than 49.5 dB, a saturation power of 26.7 dBm, a peak PAE of 20.7 % in the frequency range of 860 to 960 MHz, and a chip size of $2.14mm^2$.

• Structural Engineering and Mechanics
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• v.49 no.4
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• pp.509-521
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• 2014

In this paper two protocols of Wireless Sensor Networks (WSN) are examined through both a simulation and a case study. The simulation was performed with the optimized network (OPNET) simulator while comparing the performance of the Ad-Hoc on demand Distance Vector (AODV) and the Dynamic Source Routing (DSR) protocols. This is compared and shown with real-world measurement of deflection from eight wireless sensor nodes. The wireless sensor response results were compared with accelerometer sensors for validation purposes. It was found that although the computer simulation suggests the AODV protocol is more accurate, in the case study no distinct difference was found. However, it was shown that AODV is still more beneficial in the field as it has a longer battery life enabling longer surveying times. This is a significant finding as a large factor in determining the use of wireless network sensors as a method of assessing structural response has been their short battery life. Thus if protocols which enhance battery life, such as the AODV protocol, are employed it may be possible in the future to couple wireless networks with solar power extending their monitoring periods.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.1
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• pp.122-127
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• 2016

In this paper, new spectrum sensing schemes based on analog/RF front-end processing are introduced for IoT wireless sensor networks. While the conventional approaches for wireless channel cognition have been issued in signal processing area, the RF spectrum cognition concept makes it feasible to achieve cognitive wireless sensor networks (C-WSNs). The spectrum cognition at RF processing is categorized as four kinds of sensing mechanisms. Two recent reseaches are described as promising candidates for the C-WSN. One senses spectrum by the frequency discriminating receiver, the other senses and detects from the frequency selective super-regenerative receiver. The introduced systems with simple and low-power RF architectures play dual roles of channel sensing and demodulation. simultaneously. Therefore, introduced spectrum sensing receivers can be one of the best candidates for IoT wireless sensor devices in C-WSN environments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.575-578
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• 2004

At the present and future, the connecting net of the form to integrate the wireless with the wire have been constructed in various field, while the use of the wireless communication is increased. In the paper, We proposed and considered the standard proposal of this Zigbee(IEEE 802.15.4) which is the low price, speed and power wireless communication field and to foundation about Wireless Home Safety Supervisor System.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.3
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• pp.924-944
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• 2014

This paper investigates the power allocation and outage performance of MIMO full-duplex relaying (MFDR), based on orthogonal space-time block codes (OSTBC), in cognitive radio systems. OSTBC transmission is used as a simple means to achieve multi-antenna diversity gain. Cognitive MFDR systems not only have the advantage of increasing spectral efficiency through spectrum sharing, but they can also extend coverage through the use of relays. In cognitive MFDR systems, the primary user experiences interference from the secondary source and relay simultaneously, owing to full duplexing. It is therefore necessary to optimize the transmission powers at the secondary source and relay. In this paper, we propose an optimal power allocation (OPA) scheme based on minimizing the outage probability in cognitive MFDR systems. We also analyse the outage probability of the secondary user in noise-limited and interference-limited environments in Nakagami-m fading channels. Simulation results show that the proposed schemes achieve performance improvements in terms of reducing outage probability.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1656-1663
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• 2016

A capacitive wireless power transfer (C-WPT) system uses an electric field to transmit power through a physical isolation barrier which forms a pair of ac link capacitors between the metal plates. However, the physical dimension and low dielectric constant of the interface medium severely limit the effective link capacitance to a level comparable to the main switch output capacitance of the transmitting circuit, which thus narrows the soft-switching range in the light load condition. Moreover, by fundamental limit analysis, it can be proved that such a low link capacitance increases operating frequency and capacitor voltage stress in the full load condition. In order to handle these problems, this paper investigates optimal design of double matching transformer networks for C-WPT. Using mathematical analysis with fundamental harmonic approximation, a design guideline is presented to avoid unnecessarily high frequency operation, to suppress the voltage stress on the link capacitors, and to achieve wide ZVS range even with low link capacitance. Simulation and hardware implementation are performed on a 5-W prototype system equipped with a 256-pF link capacitance and a 200-pF switch output capacitance. Results show that the proposed scheme ensures zero-voltage-switching from full load to 10% load, and the switching frequency and the link capacitor voltage stress are kept below 250 kHz and 452 V, respectively, in the full load condition.