• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.494-510
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• 2019

Underwater acoustic communication channel parameters consist of impulse response, delay spreading, scattering function, coherence bandwidth, frequency selective fading, coherence time and time variant magnitude fading statistics on which communication system modem and channel coding are designed. These parameters are influenced by sound velocity profile, platform motion and sea surface roughness in given acoustical oceanography condition. In this paper, channel model based on phasor, channel simulator, measurement and analysis method of channel parameters are given in a fixed source-to-receiver system and the parameters are analyzed using shallow water experimental data. For two different source-to-receiver ranges of 300 m and 600 m, the parameters are characterized by three multipaths such as a direct, a surface reflection path with time variant scattering and a bottom reflection path. The results present a channel modelling method of a fixed source source-to-receiver system, channel parameters measurement and analysis methods and a system design and performance assessment method in shallow water.

• Journal of Sensor Science and Technology
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• v.14 no.1
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• pp.7-15
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• 2005

A sensor and measuring system were implemented to measure both uroflow and urophonography signal during urination for diagnose the lower urinary tract symptom. The implemented system was composed of the uroflow sensor using the load-cell, the urophonography measurement sensor so as stethoscope type, pre-processing part for sensors signal detection, amplifier and filter, system control parts and PC measurement program. A simulator of the lower urinary system that is experimental equipment implemented for evaluate the developed system. The two signals were measured using implemented system and analyzed these signal by means of time domain and frequency domain for extraction of the characteristic parameter which can most effectively reflected by the occlusion of the lower urinary system. Furthermore two signals were measured and analyzed with the subject of 5 healthy adult for clinical application possibility of the implemented system. As a result, the most influence bandwidth of effect according to occlusion of the lower urinary system is $253{\sim}282$ Hz of the urophonography signal.

• Journal of electromagnetic engineering and science
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• v.10 no.2
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• pp.73-77
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• 2010

This paper proposes a novel memory effect measurement technique in RF power amplifiers(PAs) using a two-tone intermodulation distortion(IMD) signal with a very simple and intuitive algorithm. Based on the proposed predistortive tone cancellation technique, the proposed measurement method is capable of measuring the relative phase and magnitude of the third-order and fifth-order IMDs, as well as the fundamental signal. The measured relative phase between the higher and lower IMD signal for specific tone spacing can be interpreted as the group delay(GD) information of the IMD signal concerned. From the group delay analysis, we can conclude that an adaptive control of GD as well as the magnitude and phase is a key function in increasing the linearization bandwidth and the dynamic range in a predistortion(PD) technique.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.10
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• pp.63-68
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• 2014

This paper deals with a methodology that applies the time-varying magnetic fields produced by the cloud discharges to find the direction of thunderstorm movement. We investigated the basic performance of the magnetic field measurement system composed of multi-turn loop-type sensors, the differential amplifier and active integrator. As a result, the response characteristics of the magnetic field sensor system to sinusoidal signals was excellent. The frequency bandwidth ranges from about 1 kHz to 500 kHz, the response sensitivity was 0.16mV/nT. In addition, we proposed the algorithm that determines the direction of lightning discharges using the comparison of the output signals of right-angled loop-type magnetic field sensors. The accuracy of the direction finding of lightning discharges is fairly well within the measurement error of less than $5^{\circ}$. The magnetic field measurement system proposed in this work can be used to track the direction of thunderstorm movement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.2
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• pp.111-118
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• 2004

A number of researchers have attempted to measure the reverberation time of a passenger car, ut the reverberation time of passenger car is too short to measure with the traditional band pass filter. And if the reverberation time is very short, the product of the reverberation time (T) and the bandwidth (B) of the traditional band pass fitter becomes small. The low limit of BT product required for the measurement of reverberation time with the traditional band pass filter is 16. In order to overcome this problem, the wavelet filter bank was developed. In this study, this new wavelet filter was employed to measure the reverberation times of five different classes of passenger cars. The low limit of BT product required for the measurement of reverberation time with the wavelet filter is 4. The reverberation times of five passenger cars were measured successfully with the new wavelet filter bank. The reverberation times measured in most passenger cars was found to be around 0.04. Compared with general acoustic rooms like concert halls, this is a very short reverberation time

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.6
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• pp.262-268
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• 2005

In this work, to obtain the detailed information about lightning electromagnetic field waveforms, the LabVIEW based-measurement system of time-changing magnetic fields was designed and constructed. The frequency bandwidth of the magnetic field measuring system ranges from 300 [Hz] to 1 [MHz], and the response sensitivity is 2.78 [mV/nT]. Data acquisition system with the resolution of 12 bits and memory capacity of 32 [Mbyte] was triggered by the magnetic field to be measured. The properties and parameters of the magnetic fields produced by cloud discharges were statistically investigated. The magnetic field waveforms radiated from cloud lighting discharges tend to be bipolar, with two or more narrow and several pulses superimposed on the initial front part. The recording length of the magnetic field measurement system is about 10 [ms]. The mean duration of cloud discharges is 1.3 [ms], and the number of outburst pulses for the period is 8 in average. The front times of the magnetic fields are 6.15 [$\mu$s] in average. The the zero-to-zero crossing times that is the initial half-cycle duration is widely dispersed and the mean value is 9.61 [$\mu$s], and the mean value of percentage depth of dip to opposite polarity is 41.1 [$\%$].

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.371-372
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• 2006

In this paper, we propose a method that measures quality of digital correlator. Quality of digital correlator in field of image composition of radio astronomy have as important position for acquisition of radio wave image with high precision. Digital correlator should have wide bandwidth and high precision to study on deep space. Digital correlator, therefore, should be designed to have high speed processing and high precision. But, real time measurement of quality of digital correlator using acquisition data is difficult to compare accuracy of result because digital correlator should process a large quantity of data with high speed. Measurement method of quality, also, has intricate implementation of experiment equipment. this paper present methods that compose experiment equipment without external installation easily and verify quality of digital correlator perfectly.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.7
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• pp.1206-1213
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• 1994

This paper presents the operation principle and design rule of the Rogowski coil which can measure the transient current and describes the calibration and application experimental results for performance evaluation. It is obtained that the response curves of the Robowski coil with the turns of 300 and the passive integrator to sinusoidal input give a good linearity up to the frequency of 500 [kHz] and the current measurement system gaving the Rogowski coil is the frequency bandwidth of 40 [Hz]~700 [kHz]. As an application experiment for the fabricated modeling power transmission line, the impulse current, which limitates the direct lightning return stroke to overhead ground wire, is measured by the Rogowski coil and its fast Fourier transformation is carried out. The equivalent circuit of the Rogowski coil considering the stray capacitances is proposed, and the theoretical analysis is in good agreement with the measurement results. Also, it is found that for high frequency domain the stray capacitance such as a distributed capacitance to the shield and the capacitance between windings of coil should be considered in designing the Rogowski coils since the resonance originates from the stray capacitance and the self-inductance of the Rogowski coil.

• Journal of Satellite, Information and Communications
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• v.9 no.2
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• pp.38-44
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• 2014

This paper presents design of a FMCW (Frequency Modulated Continuous Wave) level meter as well as simulation result of the designed system. The system is designed to measure maximum range of 20m since FMCW radar can be used for measuring short range distance. The distance is measured by analyzing the beat signal which is generated as result of mixing transmitting signal with the reflected received signal. The Fast Fourier Transform is applied to analyze the beat signal for calculating the displacement and Zoom FFT technique is used to minimize measurement error as well as increase the resolution of the measurement. The resolution of the measurement of the designed system in this paper is 2.2mm and bandwidth of 1.024GHz is used for simulation. Thus the simulation results are analyzed and compared in various conditions in order to get a comprehensive idea of frequency resolution and displacement resolution.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.652-654
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• 2005

인터넷에서의 효율적인 스트리밍 서비스(Streaming Service)를 위해서는 안정된 전송률의 보장이 중요하며, 네트워크의 대역폭이 제한적이기 때문에 네트워크를 공유하는 경쟁 트래픽의 형평성에 대한 고려도 필요하다. 이러한 필요성에 따라 멀티미디어 데이터 전송의 주요 프로토콜인 UDP(User Datagram Protocol)에 혼잡제어 메커니즘 적용에 대한 연구가 활발히 진행되고 있으며, 대표적으로 가용대역 폭 측정을 통한 혼잡제어 기법이 있다. 이 기법은 혼잡제어를 하기 위해서 네트워크의 상태에 따라 가변하는 가용대역폭(Available Bandwidth)을 측정하고 이것을 기반으로 전송률을 조절하는 방식을 말한다. 본 논문에서는 네트워크 상태에 따라 혼잡제어를 하기 위해서 가용대역폭을 보다 빠르고 정확하게 측정하고, 이것을 기반으로 스트리밍 서비스에 맞게 전송률을 조절하는 방법을 제안하였다. 실험을 통해 본 논문에서 제안한 방법이 기존의 가용대역폭을 측정하는 스트리밍 프로토콜 보다 성능이 개선이 되었음을 확인할 수 있었다.