• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권11호
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• pp.4291-4310
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• 2015

This paper investigates the traffic offloading over unlicensed bands for two-tier multi-mode small cell networks. We formulate this problem as a Stackelberg game and apply a hierarchical learning framework to jointly maximize the utilities of both macro base station (MBS) and small base stations (SBSs). During the learning process, the MBS behaves as a leader and the SBSs are followers. A pricing mechanism is adopt by MBS and the price information is broadcasted to all SBSs by MBS firstly, then each SBS competes with other SBSs and takes its best response strategies to appropriately allocate the traffic load in licensed and unlicensed band in the sequel, taking the traffic flow payment charged by MBS into consideration. Then, we present a hierarchical Q-learning algorithm (HQL) to discover the Stackelberg equilibrium. Additionally, if some extra information can be obtained via feedback, we propose an improved hierarchical Q-learning algorithm (IHQL) to speed up the SBSs' learning process. Last but not the least, the convergence performance of the proposed two algorithms is analyzed. Numerical experiments are presented to validate the proposed schemes and show the effectiveness.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권10호
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• pp.5035-5057
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• 2019

Advancements in nanotechnology and novel nano materials in the past decade have provided a set of tools that can be used to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. In this paper, we have proposed cooperative nano communication using Power Switching Relay (PSR) Wireless Power Transfer (WPT) protocol and Time Switching Relay (TSR) WPT protocol over independent identically distributed (i.i.d.) Rayleigh fading channels in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage Probability (OP) performances for the proposed cooperative nano communication networks have been evaluated for the following scenarios: A) A single decode-and-forward (DF) relay for PSR protocol and TSR protocol, B) DF multi-relay network with best relay selection (BRS) for PSR protocol and TSR protocol, and C) DF multi-relay network with multiple DF hops with BRS for PSR protocol and TSR protocol. The results have shown that the transmission distance can be improved significantly by employing DF relays with WPT. They have also shown that by increasing the number of hops in a relay the OP performance is only marginally degraded. The analytical results have been verified by Monte-Carlo simulations.

• Journal of Information Display
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• 제8권1호
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• pp.22-25
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• 2007

Stereoscopic/autostereoscopic systems have been developed to express 3D images, but have not been successfully use in practise. In order to apply 3D display to promising applications such as advertisements and games, we developed a 42" 2D/3D switchable display. It has characteristics that do not require special glasses for 3D images, uses multi-view technology for improving 3D viewing characteristics, and has a 2D/3D switching function to express dynamic 3D contents as well as conventional 2D contents.

• 한국컴퓨터정보학회논문지
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• 제20권7호
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• pp.33-40
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• 2015

The time slot assignment problem (TSAP) or Satellite Communications scheduling problem (SCSP) for a satellite performs $n{\times}n$ ground station data traffic switching has been known NP-hard problem. This paper suggests $O(n^2)$ time complexity algorithm for TSAP of a satellite that performs $n^2{\times}n^2$ ground station data traffic switching. This problem is more difficult than $n{\times}n$ TSAP as NP-hard problem. Firstly, we compute the average traffic for n-transponder's basic coverage zone and applies ground station exchange method that swap the ground stations until all of the transponders have a average value as possible. Nextly, we transform the D matrix to $D_{LB}$ traffic matrix that sum of rows and columns all of transponders have LB. Finally, we select the maximum traffic of row and column in $D_{LB}$, then decide the duration of kth switch mode to minimum traffic from selected values. The proposed algorithm can be get the optimal solution for experimental data.

• 한국정보전자통신기술학회논문지
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• 제10권6호
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• pp.529-534
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• 2017

본 논문에서는 스마트그리드의 핵심 설비 중 하나인 반도체 응용 고주파 변압의 개발을 위한 PWM 컨버터의 PWM 생성 방식과 그 구현에 관한 논문으로, H-bridge의 cascade 방식으로 구성된 PWM 컨버터의 경우 각 H-bridge간의 전압 balancing이 항상 이슈로 대두되는 바, 이러한 불균형은 대부분의 경우 각 H-bridge에 부가되는 스위칭 부하가 각각 균형적으로 분포되는 것이 불가능하기 때문에 발생하는 것으로 이를 해결하기 위해 종래의 경우 스위칭 패턴에 복잡한 리던던시를 추가하여 해결 하였으나, 본 논문에서 적용하는 방법은 이러한 리던던시가 불필요해 제어기의 부담을 저감할 수 있다. 본 논문에서는 이러한 자동부하분담 PWM 방식(ALB-PWM)의 실 구현에 관하여 논하였다.

• Journal of Power Electronics
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• 제7권2호
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• pp.146-158
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• 2007

A multi-pulse GTO based voltage source converter (VSC) topology together with a fundamental frequency switching mode of gate control is a mature technology being widely used in static synchronous compensators (STATCOMs). The present practice in utility/industry is to employ a high number of pulses in the STATCOM, preferably a 48-pulse along with matching components of magnetics for dynamic reactive power compensation, voltage regulation, etc. in electrical networks. With an increase in the pulse order, need of power electronic devices and inter-facing magnetic apparatus increases multi-fold to achieve a desired operating performance. In this paper, a competitive topology with a fewer number of devices and reduced magnetics is evolved to develop an 18-pulse, 2-level $\pm$ 100MVAR STATCOM in which a GTO-VSC device is operated at fundamental frequency switching gate control. The inter-facing magnetics topology is conceptualized in two stages and with this harmonics distortion in the network is minimized to permissible IEEE-519 standard limits. This compensator is modeled, designed and simulated by a SimPowerSystems tool box in MATLAB platform and is tested for voltage regulation and power factor correction in power systems. The operating characteristics corresponding to steady state and dynamic operating conditions show an acceptable performance.

• 한국산업융합학회 논문집
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• 제23권6_2호
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• pp.989-998
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• 2020

Recently, demands for large-capacity electronic loads are increasing in various industries such as a reliability test for the performance of a DC power supply device or a dummy-load for improving the stability of an independent microgrid to be actively built in the future. The electronic load required in these various fields requires an operation such as a continuously variable resistance load while minimizing the switching harmonic component generated in the electric load current in order to reduce the influence of interference from the load peripheral device. Electronic loads require a system that minimizes switching current ripple for load control. Therefore, in this paper, we propose a three-level module converter structure to reduce the current ripple of an electronic load, and a multilevel interleaved power converter topology to reduce the current ripple. The validity of the proposed electronic load, 3-level 6 interleaver converter, was verified by simulation and experiment. In addition, the user's convenience was provided by applying the emotional command curve interface method.

• 대한전자공학회논문지SD
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• 제41권5호
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• pp.15-21
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• 2004

본 논문에서는 저전력 스위치에 사용되는 소자의 포화전압 특성을 개선하기 위해 새로운 구조의 BJT를 제안하고 있다 기존에 사용되던 finger transistor(FT)의 경우 포화전압이 높아 저전력 소자의 특성을 만족하지 않아 multi base island transistor(MBIT)로 구조를 변경함으로써 저전류 영역에서의 포화전압은 충분히 낮아 저전력용 소자의 특성을 만족하지만, 이 역시 고전류 영역에서는 여전히 포화전압이 높아져 저전력용 소자의 특성을 만족하지 못하는 문제가 발생한다. 이에 본 논문에서는 folded back electrode를 이용한 새로운 구조의 BJT(FBET)를 제안하여 그 특성을 조사하였다. 새로운 구조의 트랜지스터를 적용함으로써 MBIT 구조에 비해 에미터 면적은 35 % 증가하고 접촉창의 면적이 92 % 증가하여, 저 전류 영역에서의 포화 전압은 30 % 감소하였고 고 전류 영역에서의 포화 전압은 에미터 면적 증가와 에미터 접촉 창 면적 증가에 의해 각각 30 %와 7 %씩 감소하여 전체적으로는 37 %가 감소하는 특성을 나타내었다.

• Journal of Power Electronics
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• 제16권2호
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• pp.464-472
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• 2016

This study applies the selective harmonic elimination (SHE) technique to design and operate a regulated AC/DC/AC power supply suitable for maritime military applications and underground trains. The input is a single 50/60 Hz AC voltage, and the output is a 400 Hz regulated voltage. The switching angles for a multi-level inverter and transformer turns ratio are determined to operate with special connected transformers with equal power ratings and produce an almost sinusoidal current. As a result of its capability of directly controlling harmonics, the SHE technique is applicable to apparatus with congenital immunity to specific harmonics, such as series-connected transformers, which are specially designed to equally share the total load power. In the present work, a single-phase 50/60 Hz input source is rectified via a semi-controlled bridge rectifier to control DC voltage levels and thereby regulate the output load voltage at a constant level. The DC-rectified voltage then supplies six single-phase quazi-square H-bridge inverters, each of which supplies the primary of a single-phase transformer. The secondaries of the six transformers are connected in series. Through off-line calculation, the switching angles of the six inverters and the turns ratios of the six transformers are designed to ensure equal power distribution for the transformers. The SHE technique is also employed to eliminate the higher-order harmonics of the output voltage. A digital implementation is carried out to determine the switching angles. Theoretical results are demonstrated, and a scaled-down experimental 600 VA prototype is built to verify the validity of the proposed system.

• 한국전자파학회논문지
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• 제30권4호
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• pp.307-313
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• 2019

Ka-대역 밀리미터파 복합모드 탐색기에 적용할 수 있는 진행파관 증폭기(traveling wave tube amplifier: TWTA)는 고전압생성부(high voltage power supply: HVPS), 변조부(grid modulator), 제어부(command & control), 고조파부(RF assembly)로 구성되는 고출력 펄스형 송신기이다. 펄스 반복 주파수(pulse repetition frequency: PRF)와 전원공급기 스위칭 주파수가 동기/가변되어 -17.9 kV 고전압을 생성하는 고전압 전원 공급기와 RF 펄스 변조를 위한 고속 그리드 스위칭 변조기를 설계하였다. 체적이 3.18 L로 소형화로 제작된 TWTA는 그리드 on/off 신호의 상승/하강시간이 최대 18.5 ns 이하 고속펄스 스위칭 특성을 가지고, 첨두전력은 564.9 W 이상으로 고출력 성능을 보였다. 또한 PRF와 PRF/2 범위 내에서 -68.4 dBc 이하의 우수한 불요파 성능을 확인하였다.