• 전기전자학회논문지
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• 제22권3호
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• pp.800-804
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• 2018

본 논문에서는 차동 직교 위상 편이 변조 방식 (DQPSK)의 직교주파수 분할다중 (OFDM) 기반의 단파 (HF) 대역 통신시스템을 제안한다. 제안 시스템은 약 3 kHz의 대역폭에서 약 3.6 kbps의 전송속도를 지원한다. 디지털 변복조부는 32-point 고속 푸리에 변환 프로세스를 이용한다. 한편, 각각의 부반송파 데이터가 DQPSK 변조를 이용한다. 그래서, 복조기는 반송파 위상 복구 회로와 심볼 타이밍 복구 회로를 필요로 하지 않는 장점이 있다. 또한, 각 부반송파는 개별적으로 CRC 오류 검출 코드를 사용함으로서, 다중경로 페이딩에 의한 비트 오류를 간단히 해결할 수 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1225-1230
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• 2003

In this study, Real-time estimation and compensation procedure are developed for the laser interferometer. This system is designed with homodyne quadrature-phase detection method using the Laser interferometer. The errors in this system are due to noise, disturbance and undefined model dynamics. DSP(Digital Signal Processor) is applied for real time compensation of these errors. This estimator and compensation is verified with measurement test.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 D
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• pp.2559-2561
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• 2004

This paper proposes the new signal-to-noise ratio(SNR) that is different from the conventional signal-to-noise ratio (SNR) in direct-sequence code-division multiple-access communication system employing offset quadrature phase-shift keying(OQPSK) and using a chip waveform. The conventional SNR value is so different from a real SNR value. Therefore, we propose a new SNR equation approximated to real SNR. The multiple-access interference(MAI) in DS-CDMA communication system has an effect on SNR performance and MAI is concerned with the correlation functions of the chip waveform. For this reason, we considered all possible correlations of chip waveforms. In conclusion, the SNR value of proposed method is enclosed to the real SNR value.

• 한국음향학회지
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• 제27권7호
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• pp.342-349
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• 2008

수중통신 시 다중 음파 경로의 생성은 명확한 메시지전송을 어렵게하는 원인중 하나이다. 본 논문에서는 이러한 문제점의 해결을 위하여 각기 다른 경로에 따라 형성된 다중 경로간의 지연 시간을 계산하여 변조주파수변환구간을 생성하는 방법을 제안하였다. 송신단에서는 생성된 변조주파수변환구간의 크기에 따라 메시지를 분할하여 두 개의 주파수를 사용하여 QPSK(Quadrature Phase Shift Keying)방식을 교대로 호핑하여 메시지를 전송 하였다. 이에 대응하여 수신단에서는 수신된 메시지를 알고리즘 설계 시 구축한 프로토콜에 의하여 복조하여 원신호로 복원하는 적응 BISMO 알고리즘을 제안 하였고 모의실험을 통하여 적응적 변조주파수변환구간, 추정 오류율을 계산하였다.

• 한국통신학회논문지
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• 제7권4호
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• pp.167-172
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• 1982

동일 채널 간섭 및 임펄스 잡음 환경하에서 QAM 시스템의 특성을 오율의 관점에서 연구했다. 반송파대 잡음전력비, 반송파대 간섭파 전력비, 임펄스 지수 및 신호와 간섭파 간의 위상차의 함수로써 나타낸 L-level QAM신호의 오율식을 도출하여 16-QAM에 대한 수치계산을 하여 오율특성을 그래프로 보였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.709-712
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• 1988

Ultrasonic Doppler Diagnostic System utilizes the Doppler effect for measurement of blood velocity. The sign of the Doppler frequency shift represents blood flow direction. CW(Continuous-Wave) Doppler System uses quadrature detection and phase rotation method to produce simultaneous independent audio and velocity signals for forward and reverse blood flow direction in the time-domain, had been fabricated. But time-domain analyzing such as audio evaluation and zero- crossing detection for instantaneous and mean frequnecy measurement do not provide both an accurate and quantitative result. Therefore, it is necessary to adopt frequency-domain technique to improve system performance. In this paper, we describe a unit which is composed of CW Doppler System and real-time spectrum analyzer (installed TMS 32010 DSP Chip). This unit shows time-dependent spectrum variation and mean velocity of Blood signal.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 제14회 신호처리 합동 학술대회 논문집
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• pp.305-308
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• 2001

We analyze mathematically a VSB (vestigial side-band) transceiver system for the Advanced Television Systems Committee (ATSC) digital television standard and extract a near-baseband equivalent VSB channel model. This model shows the multi-path fading effect of the quadrature component on the in-phase component. Also, we obtain a simplified model of the VSB transceiver system, which is represented by convolution of the transmission signal (before modulation) and the VSB channel. This simplified model is efficiently used for simulation of VSB systems to improve its performances, especially in an equalization part. Applying the DTV channel specifications tested by the Advanced Television Test Conter (ATTC) to the channel model, we obtain an equivalent VSB channel and show the equalization result by using the conventional derision-feedback equalize (DFE).

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 2호
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• pp.259-262
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• 1998

In this paper, we have studied measurement technique for inhomogeneous residual stress using acoustic microscopy with quadrature detector. In experiment, aluminum tensile specimen with the flaw has been made and loaded by Instrone. A spherical typed acoustic transducer of center frequency 5MHz has been used for sending a longitudinal acoustic wave into a stressed specimen. It has been shown in experimental results that the phase has largely changed around the flaw that residual stress has been largely distributed and acoustic microscopy has been used in the field of residual stress measurement.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권4호
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• pp.240-245
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• 2000

The self-field losses in a long multifilamentary Bi-2223/AgMgNi tape with varying transport current, voltage tap configurations, frequency and tape arrangements were investigated. Experimental results show that the measured losses are strongly dependent on voltage gap configurations but independent on tape arrangements. All voltage taps except the center tap are found to agree well with those predicted by Norris for an elliptical conductor. The self-field losses are purely hysteretic in nature in the range of applied frequencies for the transport currents below the critical current.

• ETRI Journal
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• 제21권2호
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• pp.9-21
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• 1999

In this paper, to enhance the performance of ${\pi}$/4-DQPSK (${\pi}$/4-differential quadrature phase shift keying), the scheme using nonredundant multiple error correction is proposed and investigated. This scheme for the differential detection of ${\pi}$/4-DQPSK uses the signal output which is delayed for more than two time slots as the parity check bit and applies it to nonredundant multiple error correction. The proposed system was used for studying the performance of ${\pi}$/4-DQPSK with Nonredundant Error Correction (NEC) in additive white Gaussian noise (AWGN) and Nakagami fade modeled mobile communication channel, and it was observed that the performance increased as the error correction capability increased.