• 한국정보통신학회논문지
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• 제13권8호
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• pp.1534-1542
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• 2009

본 논문은 SSB(Single Side Band) 변조 기법을 이용하여 실제 해상에서 실험을 수행한 결과를 분석하였다. 현재 수중 통신 분야에서의 연구는 디지털 변조 기법 및 OFDM(Orthogonal Frequency Division Modulation)이나 MIMO(Multiple Input Multiple Output) 시스템을 적용하고 있으나, 실제 해상에서 사용되는 상용 통신기로는 아날로그 변조 방식을 많이 사용하고 있다. 그에 따라 본 연구에서는 한국 해양 특성에 맞는 고품질의 수중 통신기기 개발을 목적으로 실험을 수행하였다. 실험은 SSB 아날로그 변조 기법으로 경상남도 진해 연안 천해의 조건에서 수행되었으며, 실제적인 채널의 영향을 해석하기 위해 도플러 효과, 잔향 특성, 전달 특성 등을 분석하였다. 결과적으로 수중 통신에 있어서 잔향과 배에서 방사되는 잡음이 가장 큰 장애 요인임을 확인하였다.

• 한국정보통신학회논문지
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• 제16권10호
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• pp.2163-2170
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• 2012

신호수신시스템은 수신신호의 주파수, 펄스변조, 스캔 변조, 펄스내 위상변조, 펄스내 주파수 변조 등 다양한 신호에 대한 측정 및 분석능력을 보유하여야 한다. 이러한 신호수신시스템의 성능을 평가하기 위하여 신호원들을 실험실 환경에서 효율적으로 모의발생하고 다수 전파가 존재하는 실제 운영환경과 유사한 복잡한 전파환경을 모의발생할 수 있는 효율적인 신호원 발생기를 제안한다. 제안한 모의전파신호원을 신호수신시스템 개발 전 과정에 걸쳐 활용할 경우 정확한 성능 검증 및 시험 비용을 절감할 수 있다.

• Journal of Power Electronics
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• 제16권1호
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• pp.319-328
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• 2016

In this study, we first briefly introduce the effect of circulating current control on the modulation signal of a modular multilevel converter (MMC). The maximum modulation index is also theoretically derived. According to the optimal modulation index analysis and the model in the continuous domain, different DC-side output impedance equivalent models of MMC with/without compensating component are derived. The DC-side impedance of MMC inverter station can be regarded as a series xR + yL + zC branch in both cases. The compensating component of the maximum modulation index is also related to the DC equivalent impedance with circulating current control. The frequency characteristic of impedance for MMC, which is observed from its DC side, is analyzed. Finally, this study investigates the prediction of the DC voltage ripple transfer between two-terminal MMC high-voltage direct current systems under unbalanced conditions. The rationality and accuracy of the impedance model are verified through MATLAB/Simulink simulations and experimental results.

• The Korean Journal of Ecology
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• 제25권1호
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• pp.25-28
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• 2002

The advertisement call of anurans functions to attract potential mates. The dominant frequency of an advertisement call is generally getting lower with increased snout-vent length (SVL) of the caller Rana rugosa has an advertisement call tilth a particularly high frequency modulation. We conducted a playback experiment to verify the function of frequency modulation, and investigated the territorial behavior of the frog. The frog has five types of territory defense strategy. Strategy choice depended on the caller's SVL. Small males became satellites or lowered the dominant frequency of their advertisement call, whereas large males actively defended their territory with encounter calls. In response to high frequency (1107 Hz) playback, the frogs lowered their advertisement call frequency, and towered them further in response to the low frequency (1028 Hz) playback. In addition, the number of pulses in a call was increased in response to the playback. These results indicate that the frog avoids physical conflict with competitors by selecting a territory defense strategy suitable for the caller's size, and by lowering its call frequency to disguise its SVL.

• 전자통신동향분석
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• 제9권4호
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• pp.131-138
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• 1994

최근 무선통신의 활성화에 따라, V/UHF(very/ultra high Frequency) 대역에서 한정된 주파수를 효율적으로 이용하기 위한 방법의 하나로서, 점차 점유 주파수 대역의 폭을 축소하여 보다 많은 이용자를 수용하도록 무선 채널의 협대역화가 추진되고 있다. 본 고에서는 먼저 V/UHF 대역 무선 통신에서 채널의 협대역화에 관련된 기술 중에서 현재까지 사용되고 있는 FM(frequency modulation), AM(amplitude modulation) 변조 방식의 장,단점을 살펴본후, 새로운 LM(linear modulation) 변조 방식에 대한 기술적 배경 및 특성을 알아보았다. LM은 SSR(single side band)-AM이 발전한 것으로서, TTIB(transparent tone-in-band), CLT(Cartesian loop transmitter), FFSR(feed-forward signal regeneration), DSP(digital signal processing)등 4가지의 기술이 결합하여 만들어진 것이다. LM 방식에 사용된 4가지 기술을 소개하고, 기존의 변조 방식에 비해 개선된 사항에 대해 서술한다.

• 센서학회지
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• 제20권3호
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• pp.193-198
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• 2011

In this paper, we used optoelectronic feedback to generate the carrier frequency for the ASK modulation of a lighting LED. A solar cell was used for photo-detector in the feedback circuit, and the LED light was ASK modulated by controlling the ON/OFF state of the switch that is installed in the feedback loop. The oscillation frequency of the optoelectronic feedback loop was about 50 kHz and the data rate of the ASK modulation was 9.6 kbps. In experiments, the optoelectronic feedback circuit was used for the ASK modulation of a lighting LED in the transponder of a visible light identification system, and data exchange between the transponder and the reader was successfully carried out.

• ETRI Journal
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• 제41권2호
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• pp.184-196
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• 2019

Wavelet packet modulation (WPM) is a multicarrier modulation (MCM) technique that has emerged as a potential alternative to the widely used orthogonal frequency-division multiplexing (OFDM) method. Because WPM has overlapped symbols, equalization cannot rely on the use of the cyclic prefix (CP), which is used in OFDM. This study applies linear minimum mean-square error (MMSE) equalization in the time domain instead of in the frequency domain to achieve low computational complexity. With a modest equalizer filter length, the imperfection of MMSE equalization results in subcarrier attenuation and noise amplification, which are considered in the development of a bit-loading algorithm. Analytical expressions for the bit error rate (BER) performance are derived and validated using simulation results. A performance evaluation is carried out in different test scenarios as per Recommendation ITU-R M.1225. Numerical results show that WPM with equalization-aware bit loading outperforms OFDM with bit loading. Because previous comparisons between WPM and OFDM did not include bit loading, the results obtained provide additional evidence of the benefits of WPM over OFDM.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.270-274
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• 2006

This paper proposes a Chaos Pulse Width Modulation(CPWM) technique. For generating the chaotic numbers by chaos phenomenon, chaos area $\lambda$=0.99 in bifurcation tree of the proposed double tent mapping is used. A micro-controller is used for the generation of chaos numbers and triangular carrier with chaotic frequency is obtained through the process of frequency modulation according to the generated chaos numbers. The experiments are executed with the 1.5kw induction motor coupled with a 2.5A load. The experimental results show that the voltage / current spectra are spread to a chaotic range, and the switching noise of motor is reduced by the proposed method compared to the fixed frequency PWM method.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.1914-1920
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• 2014

In this paper, characteristics of blushless direct current (BLDC) motor including core loss are analyzed considering pulse width modulation (PWM) of inverter. Input voltage of BLDC motor due to PWM is calculated considering duty ratio and carrier frequency of inverter in order to control torque or speed of BLDC motor. For the calculation of core loss, the input current with harmonics due to PWM voltage is calculated by using equivalent circuit model of BLDC motor according to switching pattern and carrier frequency. Next, core loss is analyzed by inputting the currents as a source of BLDC motor for FEM. Characteristics including core loss are compared with ones without PWM waveform according to reference speed.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권12호
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• pp.608-615
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• 2003

This paper describes an implementation of a DSP (Digital Signal Processor) controlled random carrier frequency modulation for the PWM inverter for acoustic noise reduction of induction motors. Real-time generation of the random variable and RPWM(Random PWM) along with the speed control was achieved by DSP TMS320C31. The experimental results show that the voltage and current harmonics are spread to a wide band area and the power spectrum of the acoustic switching noise was spread to create a more appealing, less annoying sound. Also, the speed response of the implemented method and the conventional method is nearly similar to each other from the viewpoint of the v/f constant control.