• Journal of electromagnetic engineering and science
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• 제16권4호
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• pp.232-234
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• 2016

In this paper, the power transfer efficiencies (PTEs) of magnetic resonance (MR) wireless power transmission (WPT) and radio frequency (RF) WPT are compared as a function of the distances between resonators (or antennas). The PTE of the C-loaded loop resonators during MR WPT was theoretically calculated and simulated at 6.78MHz, showing good agreement. The PTE of the patch antennas, whose area is the same as the C-loaded loop resonator during MR WPT, was theoretically calculated using the Friis equation and the equation by N. Shinohara and simulated at 5.8 GHz. The three results from the Friis equation, the equation by N. Shinohara, and from a full wave simulation are in strong agreement. The PTEs, when using the same size resonators and antennas are compared by considering the distance between the receiver and transmitter. The compared results show that the MR WPT PTE is higher than that of the RF WPT PTE when the distance (r) between the resonators (or antennas) is shorter. However, the RF WPT PTE is much higher than that of the MR WPT PTE when the distance (r) between the resonators (or antennas) is longer since the RF WPT PTE is proportional to $r^{-2}$ while the MR WPT PTE is proportional to $r^{-6}$.

• 한국멀티미디어학회논문지
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• 제10권6호
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• pp.745-753
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• 2007

The wireless medium is known to be time-varying which could affect and result to a poor network's performance. As a solution, an opportunistic scheduling and power control algorithm based on IEEE 802.11 MAC protocol is proposed in this paper. The algorithm opportunistically exploits the channel condition for better network performance. Convex optimization problems were also formulated i.e. the overall transmission power of the system is minimized and the "net-utility" of he system is maximized. We have proven that an optimal transmission power vector may exist, satisfying the maximum power and SINR constraints at all receivers, thereby minimizing overall transmission power and maximizing net-utility of the system.

• ETRI Journal
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• 제38권5호
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• pp.941-951
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• 2016

In this paper, cognitive radio and simultaneous wireless information and power transfer (SWIPT) are effectively combined to design a spectrum-efficient and energy-efficient transmission paradigm. Specifically, a novel SWIPT-based primary-secondary cooperation model is proposed to increase the transmission rate of energy/spectrum constrained users. In the proposed model, a multi-antenna secondary user conducts simultaneous energy harvesting and information forwarding by means of power splitting (PS), and tries to maximize its own transmission rate under the premise of successfully assisting the data delivery of the primary user. After the problem formulation, joint power splitting and beamforming optimization algorithms for decode-and-forward and amplify-and-forward modes are presented, in which we obtain the optimal PS factor and beamforming vectors using a golden search method and dual methods. Simulation results show that the proposed SWIPTbased primary-secondary cooperation schemes can obtain a much higher level of performance than that of non-SWIPT cooperation and non-cooperation schemes.

• 한국항행학회논문지
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• 제22권2호
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• pp.148-153
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• 2018

본 논문에서는 복수 수신기에 전력을 전송하기 위한 SIMO (single-input multiple-output) 자기공진방식 무선전력전송 시스템을 제안하고, 이에 따른 시뮬레이션 및 측정결과를 제시하였다. 지름 600 mm 의 송신 단일루프 및 송신 헬리컬 공진 코일, 외경 900 mm 스파이럴 수신 공진 코일을 사용하고, $80{\times}60mm^2$ 평판 사각 코일을 수신으로 활용하여 600mm 떨어진 테이블 형태 구조로 무선전력전송 시스템을 구성하였다. 최적의 특성을 위해 무선전력전송 코일을 설계하고 3차원 전자계해석 및 등가회로 해석 시뮬레이션을 진행하고 이를 제작하여 전송 특성을 측정하였다. 스파이럴 공진코일의 중심부에서 거리에 따른 효율변화를 해석하였으며, 구성한 시스템의 측정결과 수신기가 1개일 경우의 효율은 57 % 이며, 2개로 수신될 경우 각각 37 %의 전송 효율을 나타내었다.

• 조명전기설비학회논문지
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• 제26권1호
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• pp.75-81
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• 2012

In this paper, the wireless power transfer system using the magnetic resonance was designed, analyzed by circuit analysis methode and the calculated transfer function was compared with the measured one. The self-resonant coil was made up of the commonly used capacitor which had the lumped capacitance and it enabled the stable magnetic resonance not to be affected by the circumstance. The transmission efficiency of this system was 70[%] at the 15[cm] between the transmission and receiving coil and the measured transfer function was similar to the calculated one, which means the circuit analysis methode is valid in this system. When the intermediate coils were added between the transmission and receiving coil, the transmission efficiency was increased, which produced the increase of transfer distance. In the case of the five intermediate coils adding, the 35[%] transmission efficiency was achived at the 90[cm] distance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권4호
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• pp.1390-1405
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• 2014

This paper investigates optimal relay selection and power allocation under an aggregate power constraint for cooperative wireless sensor networks assisted by amplify-and-forward relay nodes. By considering both transmission power and circuit power consumptions, the received signal-to-noise ratio (SNR) at the destination node is calculated, based on which, a relay selection and power allocation scheme is developed. The core idea is to adaptively adjust the selected relays and their transmission power to maximize the received SNR according to the channel state information. The proposed scheme is derived by recasting the optimization problem into a three-layered problem-determining the number of relays to be activated, selecting the active relays, and performing power allocation among the selected relays. Monte Carlo simulation results demonstrate that the proposed scheme provides a higher received SNR and a lower bit error rate as compared to the average power allocation scheme.

• 한국전자파학회논문지
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• 제23권8호
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• pp.985-994
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• 2012

본 논문에서는 wireless body area network(WBAN) 채널을 분석하기 위해 실제 채널을 측정하고, 그것의 통계적 특성들을 조사하였다. On-/off-body 채널에서, 인체의 움직임을 고려하기 위해 대표적인 움직임들을 같이 측정하여 그 분석 결과들을 비교하였다. 또한, 세 종류의 신호 전송 기법을 제한된 Outage 확률을 가질 때 최소 소비 전력을 분석하여, 이론적인 총 전력 소비를 계산하였다. 그리고 채널 측정 데이터들을 통해 이론과 실제의 차이를 분석하였다. 본 논문의 결과로 협력 통신을 통하여 전송 효율을 높일 수 있음을 알 수 있으며, 센서 노드의 부착 위치와 움직임이 신호 전송 전력에 어떠한 영향을 미치는지 확인할 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권3호
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• pp.1599-1610
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• 2019

Intelligent services have expanded as Internet of Things (IoT) technology has evolved and new requirements emerge to accommodate various services. One new requirement is transmitting data over long distances with low-power. Researchers have developed low power wide area (LPWA) network technology to satisfy the requirement; this can improve IoT network infrastructure and increase the range of services. However, network coverage expansion causes several problems. The traffic load is concentrated at a specific gateway, which causes network congestion and leads to decreased transmission efficiency. Therefore, the approach proposed in this paper attempts to recognize and then avoid congestion through gateway channel hopping. The LPWA network employs multiple channels, so wireless channel hopping is available in a gateway. Devices that are not delay sensitive wait for the gateway to reappear on their wireless channel; delay sensitive devices change the wireless channel along the hopping gateway. Thus, the traffic load and congestion in each wireless channel can be reduced improving transmission efficiency. The proposed approach's performance is evaluated by computer simulation and verified in terms of transmission efficiency.

• 한국멀티미디어학회논문지
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• 제21권5호
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• pp.592-598
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• 2018

In wireless sensor networks where there is no centralized base station, each node has limited transmission range and the multi-hop routing for transmitting data to the destination is the one of the important technical issues. In particular, the wireless sensor network is not powered by external power source but operates by its own battery, so it is required to maximize the network life through efficient use of energy. To balance the power consumption, the residual power based adaptive power control is required in routing protocol. In this paper, we propose a routing protocol that prolongs the network lifetime by balancing the power consumption among the nodes by controlling the transmit power according to the residual power. We evaluate the proposed routing protocol using extensive simulation, and the results show that the proposed routing scheme can balance the power consumption and prolong network lifetime.

• 전기학회논문지
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• 제68권1호
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• pp.207-214
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• 2019

A large-capacity wireless power system is a technology that transmits electric power of kW or more in a noncontact type. Electric cars, electric buses, and electric railways. In order to increase the power transmission efficiency, a resonance method using a frequency of kHz is applied and the efficiency is 80 ~ 90%. In this case, the loss is 10 ~ 20% other than efficiency, and corresponds to several hundreds of W to several kW in kW class wireless power transmission. 35 kW wireless feed system environment, and induced current in the nearby conductive part was measured. As a result of analysis, it was confirmed that induction phenomenon is higher as the loop configuration of the conductive part per area is dense. The increase of the induced current in the mesh loop is characterized by the density of the nearby conductive part having a permeability per unit area. The concentration of the magnetic field by the permeability is increased and the induction phenomenon causing the induction current is increased. It was confirmed that induction phenomenon increases by about 2.7 times when 9 times dense structure is formed.