• Journal of the Optical Society of Korea
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• 제20권4호
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• pp.451-463
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• 2016

The misalignment errors and fluctuations in irradiance due to atmospheric turbulence can severely degrade the performance of free-space optical (FSO) systems. In this paper, we investigate the asymptotic bit error rate (BER) performance and diversity orders of FSO links using parallel transmit-diversity schemes. The BER expressions of FSO links with the switch-and-examine transmit (SET), switch-and-examine transmit with post-selection (SETps), dual-branch transmit laser selection (Dual-TLS), and group transmit laser selection (Group-TLS) schemes are derived, based on an approximate channel model. Then numerical simulations for these four schemes in the region of high average signal-to-noise ratio (SNR) are presented under different channel conditions. The results show that the four transmit-diversity schemes can reduce system complexity and overcome the limitation of peak power, without much BER deterioration.

• Journal of electromagnetic engineering and science
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• 제6권4호
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• pp.209-216
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• 2006

This paper investigates a distinct set of complex unitary matrices for QPSK differential space time coding. After properly selecting the initial transmission matrix and unitary matrices we find that the different combinations of them could lead different BER performance over slow/fast Rayleigh fading channels and antennas correlated channels. The numerical results show that the proper selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

• International Journal of Aeronautical and Space Sciences
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• 제1권2호
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• pp.50-67
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• 2000

The spacecraft simulator is used for command validation, operational check of the Satellite Operation Subsystem (SOS), spacecraft anomaly analysis support, satellite operator training etc. In this paper, S/W design features and modeling characteristics of the KOMPSAT Spacecraft Simulator Subsystem (SIM) are described. Validation procedures and simulation results are also provided. The SIM provides extensive simulation capabilities by including models for most of the spacecraft subsystems. The software structure of the SIM was designed and implemented so as to support operations not only in real-time but also in non real-time by utilizing the Hewlett Packard (HP) UNIX functions. The SIM incorporates as many user-friendly Man Machine Interface (MMI) windows as possible so that all the SIM normal operations can be executed through the MMI windows.

• ETRI Journal
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• 제28권5호
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• pp.680-683
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• 2006

One objective in developing the next generation of wireless communication systems is to increase data rates and reliability. A promising way to achieve this is to combine multiple-input and multiple-output signal processing with a space-time coding scheme, which offers higher coding and diversity gains and improves the spectrum efficiency and reliability of a wireless communication system. It is noted, however, that time delay differences and phase differences among different channels increase symbol interference and degrade system performance. In this letter, we investigate phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for the Rayleigh fading model to minimize their effects.

• 한국통신학회논문지
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• 제30권6C호
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• pp.481-489
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• 2005

In this letter, we propose an efficient training sequence structure for adaptive linear multiuser detectors in space-time block coded multiuser systems, by exploiting a particular property of the minimum mean square error multiuser detectors used in these systems. The proposed structure wastes less overall system capacity than the straightforward training structure, without any corresponding loss of performance, as confirmed by the simulation results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1086-1087
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• 2007

This paper presents a implementation of speed sensorless vector control algorithm of induction motor using MATLAB/SIMULINK. The proposed method utilize the combination of the voltage model based on stator equivalent model and the current model based on rotor equivalent model, which enables stable estimation of rotor flux. Estimated rotor speed, which is used to speed controller of induction motor, is based on estimated flux. The overall system consisted of speed controller with the most general PI controller, current controller, flux controller. Speed sensorless vector control algorithm is implemeted as block diagrams using MATLAB/SIMULINK. Realtime control is perform by dSPACE DS1104 control board and Real-Time-Interface(RTI).

• Current Optics and Photonics
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• 제8권3호
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• pp.239-245
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• 2024

This paper proposes single logarithmic amplification (single-LA) and deep learning (DL)-based fixed-threshold on-off keying (OOK) detection for free-space optical (FSO) communication. Multilevel LAs (MLAs) can be used to mitigate intensity fluctuations in the received OOK signal by their nonlinear gain characteristics; however, it is ineffective in the case of high scintillation, owing to degradation of the OOK signal's extinction ratio. Therefore, a DL technique is applied to realize effective scintillation compensation in single-LA applications. Fully connected (FC) networks and fully connected neural networks (FCNN), which have nonlinear modeling characteristics, are deployed in this work. The performance of the proposed method is evaluated through simulations under various scintillation effects. Simulation results show that the proposed method outperforms the conventional adaptive-threshold-decision, single-LA-based, MLA-based, FC-based, and FCNN-based OOK detection techniques.

• 한국지역지리학회지
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• 제12권2호
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• pp.245-264
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• 2006

많은 개념적 연구와 담론에 의하면, 정보통신기술의 발달은 일상생활의 시공간적 활동에 지대한 영향을 미치고 있다. 그러나 이에 관한 경험적 연구들은 실제 그 영향이 그렇게 크지 않다는 점을 보이고 있다. 이러한 양 입장을 벗어나기 위해, 이 논문에서는 정보통신기술의 발달과 사회공간에 미치는 영향에 관한 연구는 개별 현상이나 의식에 초점을 두기보다는 사회공간적 관계, 즉 네트워크의 변화에 관심을 주어야 한다는 점을 주장한다. 카스텔(Castells), 어리(Urry) 등이 주장하는 바와 같이, 사실 정보기술의 발달은 새로운 정보네트워크의 창출을 의미하며, 그 공간적 측면을 이해하기 위해 '네트워크 사회공간'이라는 용어를 사용할 수 있고, 라투어(Latour) 등이 주장하는 '행위자-연결망'이론이 원용될 수 있다. 이 논문에서는 특히 새로운 사회공간을 구성하는 네트워크는 즉시적 층위, 기능적 층위, 그리고 물질적 층위를 가지는 것으로 이해한다. 또한 네트워크사회공간은 새로운 사회공간적 관련성으로서 중요성을 가질 뿐만 아니라, 네트워크의 결절을 형성하는 주체들의 참여와 이를 통한 정체성의 재구성이라는 점에서도 중요한 의미를 가진다는 점이 강조된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.245-246
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• 2008

This paper is proposed a high performance speed control of the Synchronous Reluctance Motor through the FNN(Fuzzy Neural-Network) based SV-PWM(Space Vector PWM). SV-PWM is controlled using FNN control. SV-PWM can be maximum used maximum dc link voltage and is excellent control method due to characteristic to reducing harmonic more than others. The hybrid combination of fuzzy control and neural network will produce a powerful representation flexibility and numerical processing capability. Simulation results are presented to show the validity of the proposed algorithm.

• 한국실내디자인학회논문집
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• 제16권1호
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• pp.119-125
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• 2007

Changing depends on the one and only out of many design elements constituting the outside, and a Lighting design has an easy characteristic among space. Therefore accuse various sensitivity to watch when lighted up the same environment with Lighting of other colors, and it is an interesting point to show a communication tendency of a Lighting design in the present age escape from a general idea transmit a change of sight to a man of experience directly, and to clarify space simply, and to show various power of expression. The study of a book tried to make a searching examination for a generation cause of this tendency by trying to observe the modern Lighting design tendency that various desires were reflected in of the modern society in various general ideas of communication.