• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.309-313
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• 2009

In this paper, the network performance of a turbo coded optical code division multiple access (CDMA) system with cross-layer, which is between physical and network layers, concept is analyzed and simulated. We consider physical and MAC layers in a cross-layer concept. An intensity-modulated/direct-detection (IM/DD) optical system employing pulse position modulation (PPM) for satellite broadcasting communications is considered. In order to increase the system performance, turbo codes composed of parallel concatenated convolutional codes (PCCCs) is utilized. The network performance is evaluated in terms of bit error probability (BEP). From the simulation results, it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding and decoding complexity. Also, it is confirmed that the performance of such an optical CDMA network can be substantially improved by increasing the interleaver length and the number of iterations in the decoding process. The results of this paper can be applied to implement the satellite broadcasting communications.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1496-1504
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• 2019

This paper proposes a new THD reduction algorithm for modular multilevel converters (MMCs) with offset voltage injection operated in nearest level modulation (NLM). High voltage direct current (HVDC) is actively introduced to the grid connection of offshore wind powers, and this paper deals with a voltage generation technique with an MMC for wind power generation. In the proposed method, third harmonic voltage is added for reducing the THD. The third harmonic voltage is adjusted so that each of the pole voltage magnitudes maintains a constant value with a maximum number of (N+1) levels, where N is the number of sub-modules per arm. By using the proposed method, the THD of the output voltage is mitigated without increasing the switching frequency. In addition, the proposed method has advantageous characteristics such as simple implementation. As a part of this study, this paper compares the THD results of the conventional method and the proposed method with offset voltage injection to reduce the THD. In this paper, simulations have been carried out to verify the effectiveness of the proposed scheme, and the proposed method is implemented by a HILS (Hardware in the Loop Simulation) system. The obtained results show agreement with the simulation results. It is confirmed that the new scheme achieved the maximum level output voltage and improved the THD quality.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.447-450
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• 2009

In this paper, binary pulse-antipodal modulation (2PAM) direct-sequence (DS) ultra-wideband (UWB) system is applied to multiple input multiple output (MIMO) system using vertical bell lab layered space-time (V-BLAST) structure to achieve high-data-rate communications over indoor wireless channels. The relationship between antenna dimension and BER performance of 2PAM DS UWB MIMO system is discussed. In the receiver of UWB-MIMO system, various MIMO detection algorithms such as zero-forcing (ZF), ZF-ordered successive interference cancellation (OSIC), minimum-mean-square-error (MMSE), MMSE-OSIC and maximum likelihood (ML) are comparatively studied.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.75-83
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• 2003

Diode laser absorption system is advantageous of their non-invasive nature, fast response time, high sensitivity and real-time measurement capability. Furthermore, recent advances in room-temperature, near-IR and visible diode laser sources for telecommunication, optical data storage applications are enabling combustion diagnostics system based on diode laser absorption spectroscopy. So, combined with fiber-optics and high sensitive detection strategies, compact and portable sensor system are now appearing for a variety of applications. The objective of this research is to take advantage of distributed feed-back diode laser and develope new gas sensing system. It experimentally found out that the wavelength, power characteristics as a function of injection current and temperature. In addition to direct absorption and wavelength modulation spectroscopy have been demonstrated in these experiments and have a bright prospect to this diode laser system.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.1
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• pp.35-40
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• 2005

In this paper, we designed and fabricated the variable impedance line by using the DGS(Defected Ground Structure) which is useful in mounting the external lumped elements. Also we used a varactor diode as Control device stuff at the proposed variable impedance line. We are able to change the impedance of transmission line as varied the capacitance of varactor diode by adjusting DC bias. The impedance variation of the proposed DGS line is about maximum 70 Ω. We will study about the application of DAM(Direct antenna modulation) in the future work.

• Journal of Power Electronics
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• v.12 no.1
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• pp.24-32
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• 2012

Direct duty-ratio PWM schemes for continuous fault tolerant operation of matrix converter-fed motor drives are presented. The proposed method features simple modular modulation structure based on per output phase concept, which requires no additional modification on the normal modulation schemes for fault-tolerant applications. Realizations of fault-tolerant strategy applied to different system configurations are also treated to enhance the system flexibility. The proposed method can be effectively applied to treat the motor open phase fault and converter switching device failure. Simulation and experimental results show the feasibility and validation of the proposed strategies.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.385-386
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• 2016

직접 변조 방식(direct modulation)을 사용한 Modular Multilevel Converter(MMC)의 6개의 암 캐패시터 전압의 자연균형화(Natural Balancing) 현상은 여러 연구 및 실험에서 관측되고 있다. 또한, 이러한 현상의 원리뿐만 아니라, 시스템 파라미터와 밸런싱 동특성사이의 관계가 수학적인 분석을 통하여 검증되었다. 직접 변조 방식은 간접 변조 방식(indirect modulation)과 달리, 입/출력 AC 및 DC 측 제어기 외에 암 캐패시터 전압 밸런싱을 위한 순환전류 제어기가 존재하지 않지만, 캐패시터 맥동 저감을 위해 일반적으로 캐패시터 2 고조파 맥동 제어기를 필요로 한다. 본 논문에서는 이러한 직접 변조방식을 사용한 MMC의 2고조파 전압 맥동 제어기가 암 캐패시터 전압 자연 밸런싱에 미치는 영향을 고찰하고 분석한다. 또한, 2 고조파 전압 맥동 제어기의 유무에 따른 전압 자연 밸런싱의 동특성에 대한 비교를 400MW MMC full-scale 시뮬레이션을 통해 살펴보도록 한다.

• Journal of the Korean Society of Combustion
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• v.11 no.3
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• pp.26-35
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• 2006

This work forcus on the development of gas sensor that measure the concentrations of exhaust gas using diode laser, Each diode laser for exhaust gas measurement is set to work at near-IR using both DA and WMS methods. Also use of fiber-coupled optical elements makes such a sensor rugged and easy to align. The results showed that gas concentrations of $O_2$, CO, $CO_2$, NO are accurately measured within ${\pm}2%$ error. The application of WMS method increased the beam intensity 2-3 times higher than DA method. It were experimentally compared WMS (Wavelength Modulation Spectroscopy) with DA (Direct Absorption) for the accuracy.

• Journal of the Korean Society of Combustion
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• v.17 no.1
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• pp.12-21
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• 2012

Simultaneous measurements of oxygen concentration and temperature using diode laser in the combustion environment are successfully accomplished. A single DFB type diode laser of 760 nm line centre frequency is used and the scanned-wavelength direct absorption spectroscopy method and wavelength modulation spectroscopy method are applied to measure absorption signals below 793 K temperature region. The experimental results show that oxygen concentration are measured within 1% accuracy and temperature are measured within 5% accuracy. This new method of simultaneous measurements of concentration and temperature with a single diode laser shows a great promise.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.4
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• pp.1077-1088
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• 1996

In this paper, we propose a new method to analyze the performance degradation by timing jitters in the receivers of intensity modulation/direct detection digital optical communication systems where pulse-shaping filters are used to minimize intersymbol interference. The results obtained from the proposed analytical method show that conventional analytical methods underestimate the influence of timing jitters on the receiver performance. Using the proposed anlaytical method, we derive an analytic equation for approximated power penalty due to timing itters and obtain an exact power penalty by numerical analyses. Assuming Gaussian or uniform probability density function for timing jitters, we also show that assumption of Gaussian distribution for timing jitters yields more performance degration than that of uniform distribution.