• The Journal of the Acoustical Society of Korea
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• v.13 no.6
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• pp.24-30
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• 1994

In this paper, the system for detection of photoacoustic signal has been constructed by using CW $CO_{2}$ laser for an analysis of the photoacoustic signal In metals and aluminum carbon steel, brass have been used as sample. The photoacoustic signals of several nano amperes have been detected in each sample with varying modulation frequency of laser, time constant of lock-in amplifier, thickness of sample. The characteristics of photoacoustic signal has been analysed in term of phase angle by using signal processing technique. Results indicate that the photoacoustic signal can be stabilized by adjustment of time constant of lock-in amplifier, that the signal amplitude is proportional to the ratio of thermal expansion coefficient to thermal capacity of metal, and that the signal amplitude decreases exponentially with sample thickness as well as with modulation frequency.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.2
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• pp.8-18
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• 1997

In this paper, a New Low Loss Quasi-Parallel Resonant DC-Link(NLQPRDCL) Inverter which shows highly improved PWM capability, low loss characteristic and low voltage stress is presented. A method to minimize freewheeling interval, which is able to largely decrease DC-link operation losses and to steadily guarantee soft switching in the wide operation region is also proposed. In addition, lossless control of zero voltage duration of DC-link makes the proposed inverter maintain the advanced PWM capability even under a very low modulation index. Experiment and simulation were performed to verify validity of the proposed inverter topology.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.354-355
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• 2011

그 동안 스위칭 손실 저감을 위해 Si 다이오드를 SiC 다이오드로 대체한 인버터들이 많이 소개되었다. NPC 인버터에서도 마찬가지로 클램프 다이오드 소자를 SiC 다이오드로 대체함으로써 스위칭 손실을 저감시킬 수 있다. 하지만 IGBT의 스위칭 손실이 매우 크기 때문에 단지 클램프 다이오드 소자를 바꿈으로써 줄일 수 있는 스위칭 손실은 한계가 있다. 따라서 본 논문은 낮은 변조지수를 갖는 NPC 인버터에서 역회복 손실을 포함한 스위칭 손실을 최소화 시킬 수 있는 새로운 PWM 방법을 제시한다. 제안한 방법에 의해 역회복 현상은 거의 발생하지 않으며 스위칭 손실은 상당히 저감된다. 그러므로 전체 시스템 효율을 증가시킬 수 있고 인버터를 더 높은 스위칭 주파수에서 동작시킬 수 있다. 제안한 방법의 타당성은 각 소자의 성능평가와 수치해석적 방법을 적용해 검증하였다.

• Journal of Broadcast Engineering
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• v.12 no.1 s.34
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• pp.2-10
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• 2007

We analyzed the receiving performance of the DVB-S2 transmission system in the BC(Backward Compatibility) mode. The transmitter employs the hierarchical modulation, and the receiver can be implemented by the direct demodulation or the hierarchical demodulation. The performance of each demodulation scheme is analyzed by a statistical method and a computer simulation for the AWGN and nonlinear channels. The ratio of the LP/HP streams which is proper in the domestic satellite broadcasting environments, is also suggested.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.499-504
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• 2002

In this paper, we analyzed the performance of FH/CPFSK system with differential detection in thermal noise, partial-band jamming noise and adjacent interference of all eight bit pattern. The parameters to analize performances of FH/CPFSK system have been used the bit rate, modulation index and performances of FH/CPFSK system with the differential detector have been presented with the optimum correlation function. And, we were compared with performance of FH/CPFSK and FH/BFSK system. In result, we could know that bit error probability of the approximation equation and exact equation nearly accorded in the high signal-to-noise ratio. And, we have been proved that FH/CPFSK system with differential detection according to jamming fraction ${\gamma}$ was worst to 3dB than FH/CPFSK system with limiter-discriminator. but was superior to 2dB than FH/BFSK.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.10
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• pp.2165-2170
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• 1997

In this paepr, the distortion effects of impairments in CDMA transmitter system were analyzed. We considered not only linear distortion effects, for example, I/Q imbalance, quadrature offset and carrier leakage, but also nonlinear distortion effects such as AM-AM and AM-PM noise in power amplifier. To investigate how the impariments impact on the performance of CDMA transmitter, all effects represented as a function of CDMA modulation quality which is an important measure of the transmitted signal. These results show the limitation value of each impairment which is required to satisfy the IS-95 standard.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.560-564
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• 2003

This paper proposes a simple control strategy based on the discontinuous PWM(DPWM) to balance the DC-link voltage of three-level Neutral-Point-Clamped(WPC) inverters at low modulation index. New DPWM methods in multi-level inverter are also introduced. The proposed DPWM method changes the path and duration to flow the neutral point current out of or into neutral point of the DC-link and it makes the overall fluctuation of the DC-link voltage zero during a sampling time of reference voltage vector. Therefore, the voltage of the DC-link can be balanced fairly well and also the voltage ripple of the DC-link is reduced significantly. Moreover, comparing with conventional methods, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by experiment

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.173.1-173.1
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• 2012

천리안 위성 원격측정명령계 RF부는 위성 장착 이후 발사 전까지 여러 단계의 위성체레벨 기능시험을 거치며 요구 성능을 만족하는지를 충분히 확인하였다. 위성 발사후부터 정상궤도 진입 후에 발사전 원격측정명령계 RF가 원하는 요구 기능 및 성능을 만족하고 있는지를 확인하는 궤도운용시험이 수행되었다. 본 논문은 원격측정명령계 RF부의 궤도운용시험 계획에 따라 수행하여 얻어진 시험 결과에 대한 분석에 대한 것이다. 먼저 발사 후 LEOP 동안 원격명령이 정상적으로 수신되고 수행되는지 확인하였다. 그 이후 원격명령이 언락되는 수신 파워 임계(Threshold) 입력 레벨 확인을 확인하였으며 원격측정 다운링크 주파수 변이가 요구범위에 있는지 확인하였으며, 수신신호 스펙트럼 측정을 통해 TM EIRP를 추정한 결과 링크 버짓 마진 대비 추가적인 마진이 있음을 확인하였으며 또한 TM 송신 신호 변조지수가 추정범위 안에 있는지를 확인하였다. 그리고 레인징 시험을 통해 수신기 및 레인징 기능이 정상적으로 동작하고 있음을 확인하였다. 이 궤도운용시험 결과는 후속 정지궤도복합위성 원격측정명령계 RF부 궤도운용시험을 위한 비교 자료로 활용될 것이다.

• Journal of the Korea Society of Computer and Information
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• v.3 no.4
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• pp.78-85
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• 1998

In this paper, we analyzed the performances for FH/CPFSK system with limiter - discriminator detection and integrate-and-dump post-detection filtering under thermal noise and partial-band jamming noise. And, we considered intersymbol interference - related SNR and differential phase parameters for all eight of the possible adjacent bit data patterns, FM noise clicks for evaluating FH/CPFSK and CPFSK systems. In result, the optimum modulation index h was 0.7 and the optimum value of bandwidth-time product D was 1.0. Next, when we considered the thermal noise under the partial-band jamming, the thermal noise significantly influenced the error probability of system below 20dB approximately but could ignore above 20dB.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.5
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• pp.229-236
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• 2014

Quadrature Amplitude Modulation (QAM) is widely used in contemporary wired and wireless communications systems. In this paper, I propose a generalized triangular quadrature amplitude modulation (gTQAM) that includes the square quadrature amplitude modulation (SQAM), TQAM, and ${\Theta}$-QAM as special cases. Therefore, the proposed gTQAM forming a lattice of arbitrary triangles provides a versatile structure in signal constellations compared to other QAM schemes. For M-ary gTQAM, I derive an exact closed-form expression for the bit error rate (BER), and present the optimal signal constellations for given SNR values from the derived BER expression. Finally, I validate the derived BER results through computer simulations.