• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.392-399
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• 2019

In this paper, we have studied wireless time division duplex(TDD) time synchronization technique considering the propagation delay between mobile vehicles. The existing IEEE 1588 precision time protocol(IEEE 1588 PTP) algorithm was applied and the time synchronization between the two nodes was achieved through the propagation delay and clock offset time correction calculated between master slave nodes during wireless TDD communication. The time synchronization process and procedure of IEEE 1588 PTP algorithm were optimized, thereby reducing the propagation delay error sensitivity for real-time moving vehicles. The sync flag signal generated through the time correction has a time synchronization accuracy of max +252.5 ns within 1-symbol(1.74 M symbol/sec, ${\pm}287.35ns$) through test and measurement, and it was confirmed that the time synchronization between master slave nodes can be achieved through sync flag signal generated during GPS disturbance.

• 전기의세계
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• v.30 no.11
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• pp.734-746
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• 1981

This paper suggests on-load torque measurement for 3 phase induction motors by input -voltage and current utilizing symmetric coordinate analysis technique on the basis of the induction motor equivalent circuit. In this paper, two cases are treated with, i.e, one is the case where the motors' exciting current and primary leakage impedance voltage drop are compensated automatically, adopting the ideal wattmeter whose current coil impedance and voltage coil impedance are 0 and .inf. respectively, and the other is the case where non-ideal wattmeter is adopted and the compensation above is made by computation. As a result of the case study, following conclusions are obtained. 1) By proper combination of the error propagation law and the limit of power consumption, the desirable overall measurement error of the apparatus can be obtained on the basis of the inherent errors of CT and PT. 2) The measurement error is larger in current simulation circuit than in voltage simulation circuit. 3) Between the two cases, the latter is more advantageous than the former from the viewpoint of feasibility and the measurement error. 4) As the attachment of Ammeter in the current simulation circuit influences the measurement error considerably, its internal impedance should be large considerably. 5) The larger the consumption power of the apparatus is, the easier the feasibility is.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.164-170
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• 2006

Millimeter waves can be used for high resolution ranging and imaging. As the necessity of high-speed multimedia communication increases, millimeter wave systems are being developed since they are useful for wide band communication considering the shortage of available spectrum bands. However, it is necessary to analyze the characteristics of millimeter propagation in the atmosphere to assess the performance of millimeter wave systems. MCF and intensity fluctuations describe atmospheric effects on millimeter wave propagation. Using the quasi-optical method, a method is investigated to obtain MCF from the intensity distribution of focal plane. Also, a practical method is proposed to compute MCF from the flux measurement in the antenna focal plane.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.2
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• pp.199-207
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• 2001

In this paper, the technique of prediction and analysis on the characteristics of propagation in indoor environment is presented. This technique needs no reception sphere commonly used in 3D-ray tracing scheme, and thereby it lends us easy code realization. The validity of developed code is verified by comparing with the values of image methods and measurement. The developed technique applied to the structure of rectangular corridor with the iron door and we calculated the path loss for the variation of the iron door angle. The path loss decreased about 15 dB at the distance of30 m from the iron door and the delay spread increased approximately by four times. Based on the computation, we confirmed that indoor propagation in PCS is heavily affected by the iron door in corridor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.688-694
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• 1998

The ability to locate the defects in materials is one of the major attrations of the acoustic emission(AE) technique. The most conventional method for planar AE source localization is to place three or more AE sensors on the plate and to determine the source position by measuring the differences in the arrival times of the AE wave at the sensors, which is called as triangulation method. But this method can not be applied in the material of which elastic wave propagtion velocity is not known. In this paper, we propose two methods, vector method and error minimization method, for AE source location on the material with unknown AE wave velocity. In this method, it is not needed to know the propagation velocity previously, that is, we can apply this method to arbitrary material of which properties are not known exactly. Also, in this paper, the robustness to the error in the measurement of time differences are discussed for both methods. Finally, in order to evaluate the actual performances, experiments using a pencil lead break as the AE source were carried out on the aluminum plate.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.5
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• pp.426-435
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• 2002

In this paper we present an indoor propagation model for indoor wireless LAN service in the ISM band. We primarily use a 3D ray tracing as well as a patch scattering model in order to take into account the indoor fixtures. Therefore input parameters such as indoor environment parameters and antenna's types, polarizations are considered. As the results, we present fading characteristics and rms delay spread from time delay spread. In order to investigate the accuracy of the presented model, comparisons of predictions with measurement and simulations are performed in indoor wireless LAN service environments. The results show that measurements and simulations are very similar. Therefore in this paper, the effect of presented indoor propagation model is confirmed.

• Journal of Sensor Science and Technology
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• v.28 no.6
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• pp.414-419
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• 2019

An ultrasonic based magnetostrictive position sensor (MPS) provides an indication of real target position. It determines the real target position by multiplying the propagation speed of ultrasonic wave and the time-of-flight between the receiving signals; one is the initial signal by an excitation current and the other is the reflection signal by the ultrasonic wave. The propagation speed of the ultrasonic wave depends on the temperature of the waveguide. Hence, the change of the propagation speed in various environments is a critical factor in terms of the positioning accuracy in the MPS. This means that the influence of the changes in the waveguide temperature needs to be compensated. In this paper, we presents a novel way to improve the positioning accuracy of MPSs using temperature compensation for waveguide. The proposed method used the inherent measurement blind area for the structure of the MPS, which can simultaneously measure the position of the moving target and the temperature of the waveguide without any additional devices. The average positional error was approximately -23.9 mm and -1.9 mm before and after compensation, respectively. It was confirmed that the positioning accuracy was improved by approximately 93%.

• Journal of Biomedical Engineering Research
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• v.14 no.1
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• pp.31-40
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• 1993

It is well known that nonlinear propagation characteristics of the wave in the tissue may give very useful information for the medical diagnoisis. In this paper, a new method to detect nonlinear propa gation characteristics of the internal vibration in the tissue for the low frequency mechanical vibra lion by using bispectral analysis is proposed. In the method, low frequency vibration of $f_0(=100Hz)$ is applied on the surface of the object, and the waveform of the internal vibration ${\times}{\;}(t)$ is measured from Doppler frequency modulation of silmultaneously transmitted probing ultrasonic waves. Then, the bispectra of the signal ${\times}{\;}(t.)$ at the frequencies ($f_0,{\;}f_0$) and ($f_0,{\;}2f_0$) are calculated to estimate the nonlinear propagation characteristics as their magnitude ratio, where since bispectrum is free from the gallssian additive noise we can get the value with high S/N. Basic experimental system is con structed by using 3.0 MHz probing ultrasonic waves and the several experiments are carried out for some phantoms. Results show the superiority of the proposed method to the conventional method using power spectrum and also its usefulness for the tissue characterization.

• Journal of Positioning, Navigation, and Timing
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• v.8 no.4
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• pp.183-192
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• 2019

In fingerprint-based wireless positioning, it is necessary to establish a DB of the unmeasured area. To this end, a method of estimating the position of a base station based on a signal propagation model, and a method of estimating the information of the received signal in the unmeasured area based on the estimated position of the base station have been investigating. The purpose of this paper is to estimate the position of the base station using the measured information and to analyze the performance of the positioning. Vehicles equipped with a GPS receiver and signal measuring equipment travel the service area and acquire location-based Reference Signal Received Power (RSRP) measurements. We propose a method of estimating the position of the base station using the measured information. And the performance of the proposed method is analyzed on a simulation basis. The simulation results confirm that the accuracy of the positioning is affected by the measured area and the Dilution of Precision (DOP), the accuracy of the position information obtained by the GPS receiver, and the errors of the signal included in the RSRP. Based on the results of this paper, we can expect that the position of the base station can be estimated and the DB of the unmeasured area can be constructed based on the estimated position of the base stations and the signal propagation model.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.208-215
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• 2012

The acoustic noise around a launch pad by launches of space launch vehicles was analyzed. The magnitudes of sound noise at some points near launch pad were predicted by locating the sound source at the exhaust jet plume of the rocket engine and considering several factors such as the directivity of the sound propagation and atmospheric attenuation. Specifically, the launch noise of Korea Space Launch Vehicle-I (KSLV-I) was estimated, and was compared to the actual measurement results. The analysis results proved to be heavily affected by the characteristics of directivity of sound propagation and the analysis showed good agreements with the measurements when the directivity of the sound was appropriately adjusted.