• 한국통신학회논문지
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• 제31권3A호
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• pp.282-290
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• 2006

본 논문에서는 2.45GHz 대역 IEEE 802.15.4 LR-WPAN(Low-Rate Wireless Personal Area Network; ZigBee) 시스템의 수신기를 위한 개선된 방식의 Timing estimator의 알고리즘을 제안한다. 저가 구현을 지향하는 LR-WPAN 시스템의 특성상 고가의 오실레이터를 사용할 수 없으므로 반송파 중심 주파수의 80ppm에 해당하는 주파수 옵셋 환경에서 안정된 동작이 가능한 Timing estimator 알고리즘이 요구된다. 본 논문에서는 이러한 수신 환경을 고려하여 Multiple delay differential filter를 적용함으로써 주파수 옵셋에 대한 강인성 및 수신 성능의 안정성을 증대시켰으며, Multiple delay differential filter의 출력 신호에 대한 reference 신호의 상관 결과가 I-channel 에만 국한되는 특성을 이용하여 일반적인 noncoherent 방식 대신 coherent 방식의 correlator를 적용함으로써 non-coherent 방식의 제곱 손실을 제거하여 검출 성능을 향상시킴과 동시에 복잡도를 감소시켜 초소형, 저전력, 저가를 지향하는 LR-WPAM 수신기에 보다 적합하도록 설계하였다. 다양한 채널 환경에서의 성능정가를 통하여 제안된 알고리즘이 differential detection 기반의 noncoherent 방식보다 평균적으로 2dB의 향상된 성능을 보임을 입증하였다.

• 한국전기전자재료학회논문지
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• 제25권2호
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• pp.147-152
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• 2012

This paper dealt with the frequency component analysis of acoustic signals produced by corona and series-arc discharges as a diagnostic technique for closed-switchboards. Corona and series-arc discharge were simulated by a needle-plane electrode and an arc generator specified in UL1699, respectively. Acoustic signal was detected by a wideband acoustic sensor with a frequency bandwidth of 4 Hz~100 kHz (-3 dB). We analyzed frequency spectrums of the acoustic signals detected in various discharge conditions. The results showed that acoustic signals mainly exist in ranges from 30 kHz to 60 kHz. From the experimental results, an acoustic detection system which consists of a constant current power supply (CCP), a low noise amplifier (LNA) and a band pass filter was designed and fabricated. The CCP separates the signal component from the DC source of acoustic sensor, and the LNA has a gain of 40 dB in ranges of 280 Hz~320 kHz. The high and the low cut-off frequency are 30 kHz and 60 kHz, respectively. We could detect corona and series-arc discharges without any interference by the acoustic detection system, and the best frequency is considered in ranges of 30 kHz~60 kHz.

• Journal of Magnetics
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• 제18권3호
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• pp.357-360
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• 2013

A modified SQI method using magnetic leakage flux (MFL) signal for underground gas pipelines' defect detection and characterization is presented in this paper. Raw signals gathered using MFL signals include many unexpected noises and high frequency signals, uneven background signals, signals caused by real defects, etc. The MFL signals of defect free pipelines primarily consist of two kinds of signals, uneven low frequency signals and uncertain high frequency noises. Leakage flux signals caused by defects are added to the case of pipelines having defects. Even though the SQI (Self Quotient Image) is a useful tool to gradually remove the varying backgrounds as well as to characterize the defects, it uses the division and floating point operations. A modified SQI having low computational complexity without time-consuming division operations is presented in this paper. By using defects carved in real pipelines in the pipeline simulation facility (PSF) and real MFL data, the performance of the proposed method is compared with that of the original SQI.

• 한국전자파학회논문지
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• 제27권10호
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• pp.909-916
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• 2016

비콘 수신기는 위성에서 송출된 비콘 신호를 검출하여 그 신호세기를 측정하는 장치이다. 위성에서 송출된 비콘 신호는 지구국의 안테나를 목표 위성 방향으로 이동시키는 포지셔너의 조정 및 송신출력 제어 목적을 위한 것으로 무변조 저전력 연속파(CW)로 구성되어 있다. 일반적으로 비콘 신호 검출은 협대역 아날로그 필터를 사용한 RSSI(Received Signal Strength Intensity) 방식이 대표적으로 사용되고 있으나, 온도변화 및 장시간 동작에 따른 위성 송출 비콘 주파수 변동이 발생됨에 따라 비콘 수신기에서 주파수를 추적하는 스캔 기능 구현을 필요로 한다. 본 설계에서는 보다 빠른 비콘 신호 검출을 위하여 협대역 디지털필터를 다중 배열하여 비콘 주파수를 추적하고, SNR(Signal to Noise Ratio) 방식에 의한 비콘 신호 검출방식 수신기로 설계한다. 이를 위하여 위성과 지구국 사이의 강우감쇠를 고려한 무선채널 링크 버젯을 사용하여 비콘 신호 수신 $C/N_o$ 및 비콘 신호 검출을 위한 필요 C/N을 고려한 뒤 디지털필터의 대역폭 및 배열 개수를 도출한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5527-5545
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• 2019

Through-wall ultra-wide band (UWB) radar has been considered as one of the preferred and non-contact technologies for the targets detection owing to the better time resolution and stronger penetration. The high time resolution is a result of a larger of bandwidth of the employed UWB pulses from the radar system, which is a useful tool to separate multiple targets in complex environment. The article emphasised on human subject localization and detection. Human subject usually can be detected via extracting the weak respiratory signals of human subjects remotely. Meanwhile, the range between the detection object and radar is also acquired from the 2D range-frequency matrix. However, it is a challenging task to extract human respiratory signals owing to the low signal to clutter ratio. To improve the feasibility of human respiratory signals detection, a new method is developed via analysing the standard deviation based kurtosis of the collected pulses, which are modulated by human respiratory movements in slow time. The range between radar and the detection target is estimated using joint time-frequency analysis (JTFA) of the analysed characteristics, which provides a novel preliminary signature for life detection. The breathing rates are obtained using the proposed accumulation method in time and frequency domain, respectively. The proposed method is validated and proved numerically and experimentally.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1963-1966
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• 2004

An ultra wide band ultra-high frequency (UHF) signal processing module was designed for on-line UHF partial discharge (PD) monitoring systems for gas-insulated switchgears (GIS). Major advantage of the unit is an improved PD detection sensitivity through minimizing the effect of surrounding interference signals. The detection sensitivity of the unit was <-60 dBm that is sufficient to detect UHF PD signals as low as 1 pC. Precise detection of PD occurred in the GIS, due to internal defects, is possible by using the signal processing unit.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 춘계학술대회 논문집 전기설비전문위원
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• pp.128-131
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• 2004

An ultra wide band ultra-high frequency (UHF) signal processing module was designed for on-line UHF partial discharge (PD) monitoring systems for gas-insulated switchgears (GIS). Major advantage of the unit is an improved PD detection sensitivity through minimizing the effect of surrounding interference signals. The detection sensitivity of the unit was <-60 dBm that is sufficient to detect UHF PD signals as low as 1 pC. Precise detection of PD occurred in the GIS, due to internal defects, is possible by using the signal processing unit.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권11호
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• pp.498-502
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• 2005

The objectives of this paper are to provide information on the characteristics of the discharge signals in a low-voltage indoor outlet. Most of electrical fires are caused by short circuits, overheating of wires, deterioration and incomplete connection of wiring devices. The last two cases are predictable before the occurrence of fire because of its slow progress. We have simulated the discharge signals caused by the deterioration and incomplete connection of wiring devices using aged outlets. From the experimental data, we could characterize the frequency spectrums of the discharge signals depending on the cases. The higher frequency components of the signal are attenuated by the capacitance and inductance of power lines as the measuring point is getting away from the discharges. Main frequency components of the discharge signal are existent at 600kHz - 1.5MHz in incomplete connections and at 210H7z - 8MHz in deteriorations of the outlet.

• ETRI Journal
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• 제41권3호
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• pp.316-325
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• 2019

Accurate suppressive jamming is a prominent problem faced by radar equipment. It is difficult to solve signal detection problems for extremely low signal to noise ratios using traditional signal processing methods. In this study, a joint sensing dictionary based compressed sensing and adaptive iterative optimization algorithm is proposed to counter suppressive jamming in information domain. Prior information of the linear frequency modulation (LFM) and suppressive jamming signals are fully used by constructing a joint sensing dictionary. The jamming sensing dictionary is further adaptively optimized to perfectly match actual jamming signals. Finally, through the precise reconstruction of the jamming signal, high detection precision of the original LFM signal is realized. The construction of sensing dictionary adopts the Pei type fast fractional Fourier decomposition method, which serves as an efficient basis for the LFM signal. The proposed adaptive iterative optimization algorithm can solve grid mismatch problems brought on by undetermined signals and quickly achieve higher detection precision. The simulation results clearly show the effectiveness of the method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.43-48
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• 2008

Gear system has been widely used in industrial applications and unexpected failures of gears are not only extremely damaging but also lead to economic losses. So, early detection of fault is important for diagnosis machine condition. And acoustic emission is an efficient non destructive testing technique for the diagnosis of machine health and is useful technique for early detection of fault because it can find low-amplitude and high-frequency signal on account of high sensibility. Therefore, in this paper, the AE signal was measured and preprocessed using envelop analysis for gearbox with misalignment between pinion and gear. And then the vibration characteristic of gear misalignment was analyzed.