• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.479-486
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• 1999

In this paper the system performance degradation resulting from nonlinear transmitter power amplifier which is essential to increase the efficiency is analyzed in a forward link CDMA system. The power amplifier is modeled by power series model which includes only odd-order terms. The effects of power amplifier's nonlinearity such as intersymbol interference, phase distortion on the RF system performance were visualized by examining the distorted time domain waveforms, signal vector constellation. And through the investigation of the power spectrum density of the transmitted signal, spectral regrowth or sideband regrowth which is result from amplitude distortion can be seen. All these characteristics result in BER performance degradation due to other user interferences and intersymbol interference. The analysis technique described here applies not only to power amplifier but also to any other nonlinear components such as mixers and switches. Also the effects of adjacent channel interference and supurious emission can be analysed between different systems.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.1
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• pp.27-35
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• 2009

In this paper, we study the classification of steam generator tube defects using an improved feature extraction. We consider 4 axisymmetric defect patterns of tube: I-In type, I-Out type, V-In type, and V-Out type. Through numerical analysis program based on finite element modeling, 400 ECT signals are generated by varying width and depth of each defect type. From those generated ECT signals, we propose new feature vectors that include an angle between the two points where the Maximum impedance and half the Maximum impedance, and angles between Maximum impedance point and 10%, 20%, 30%, 40% of Maximum impedance points. Also, multi-layer perceptron with one hidden layer is used to classify the defect patterns. Through the computer simulation study, it is shown that the proposed method achieves an improved defect classification performance in terms of Maximum Error and mean square Error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.9
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• pp.820-825
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• 2004

In this paper an octave tuning voltage controlled oscillator which is used in set-top TV tuner was designed. Oscillation frequency range is 0.9 GHz～2.2 GHz with 1.3 GHz bandwidth. By using 4 varactor diodes in base and emitter of transistor, wide-band tuning, sweep linearity and low phase noise could be achieved. Designed VCO requires a tuning voltage of 0 V ～ 20 V and DC consumption of 10 V and 15 mA. Designed VCO exhibits an output power of 5.3 dBm $\pm$1.1 dB and a phase noise below -94.8 dBc/Hz ＠ 10 kHz over the entire frequency range. The sweep linearity shows 65 MHz/V with a deviation of $\pm$10 MHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.4
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• pp.433-442
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• 2010

In this paper, self-calibration algorithm based on covariance matrix is proposed for compensating amplitude/phase mismatch in multi-baseline interferometer direction finding system. The proposed method is a solution to nonlinear constrained minimization problem which dramatically calibrate mismatch error using space sector concept with cost function as defined in this paper. This method, however, has a drawback that requires an estimated initial angle to determine the proper space sector. It is well known that this type of drawback is common in nonlinear optimization problem. Superior calibration capabilities achieved with this approach are illustrated by simulation experiments in comparison with interferometer algorithm for a varitiety of amplitude/phase mismatch error. Furthermore, this approach has been found to provide an exceptional calibration capabilities even in case amplitude and phase mismatch are more than 30 dB and over $5^{\circ}$, respectively, with sector spacing of less than $50^{\circ}$.

• Journal of Hydrogen and New Energy
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• v.28 no.3
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• pp.300-307
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• 2017

This study is to investigate particle size and velocity profile of gasoline port injector using Phase Doppler Particle Analyzer (PDPA). In this experiment, a GV 250 Delphi port injector used for motorcycles was used for liquid injection. The injector consists of four holes and has a static flow rate of 2.13 g/s. The fuel used in the injection was N-heptane, which is similar to gasoline, as an alternative fuel. The test fuel was injected at an atmospheric temperature of $20^{\circ}C$ and an open atmosphere of 1 atm. The injection time was 10 ms and the injection pressure was 3.5 bar in PDPA experiment. The experimental target position was fiexd at 30, 50 and 75 mm from the nozzle tip and data were collected for a total of 10,000 samples. The experimental results show that the length diameter (D10), the Sauter mean diameter ($D_{32}$), and the mean droplet velocity (MDV) are $45-54{\mu}m$, $99-115{\mu}m$ and 15-21 m/s, respectively.

• Journal of Advanced Navigation Technology
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• v.23 no.6
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• pp.570-576
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• 2019

The configuration of dispersion-managed optical link with optical phase conjugator, which is placed at the non-midway of total transmission length, is proposed for implementing of the flexible optical network. The optical phase conjugator is located between the former half transmission section and the latter half transmission section, which are consisted of 6 fiber spans and 14 fiber spans respectively, and the averaged RDPS of each half transmission section are inconsistence. And, the artificial distribution of each fiber span's RDPS, which are gradually increased/decreased as the span numbers are increased, is adopted to compensate for the distorted wavelength division multiplexed channels. From the simulation results, it is confirmed that the compensation in dispersion-managed link configured by a special distribution pattern among 16 proposed patterns, in which the RDPS of each fiber spans are gradually decreased/increased in the former/latter half section with the small deviation, is suitable to compensate for the distorted wavelength division multiplexed channels.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.903-910
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• 2020

This paper introduces a simulator to assess the impacts of the wind and the airframe vibration on the performance of the Active Electronically Scanned Array (AESA) radar mounted in an aircraft. The AESA radar is mounted on the nose cone of an aircraft, and vibration occurs due to the drag force. This vibration affects the behavior of the AESA radar and can cause phase errors in signal. The simulator adopts the geometric model for nose cone, the mathematical models on the rigid-body dynamics of the aircraft, the average/turbulent winds, and the mode/ambient vibrations to compute the position and the attitude of the radar accurately. Numerical studies reflecting a set of test scenarios were conducted to demonstrate the effectiveness of the developed simulator.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.46-52
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• 2009

In this paper, the timing estimator based on the principle of the best linear unbiased estimator (BLUE) is proposed in OFDMA uplink systems. The proposed timing estimator exploits the phase information of the differential correlation between adjacent subcarriers. The differential correlation can extract the information about timing offset and mitigate the distortion of the signal caused by the frequency selectivity of channel. Compared with conventional methods, the proposed estimator shows more accurate capability in estimation. In addition, the estimator is hardly affected by the distortion caused by the frequency selectivity of channel. Simulation results confirm that the proposed estimator shows a small error mean and a relatively small error variance. In addition, the performance of the estimator is evaluated by means of SNR loss. It is shown by simulations that the SNR loss of the proposed estimator by estimation errors is less than 0.4 dB for the SNR values between 0 and 20 dB. This might indicate that the proposed estimator is suitable for the timing synchronization of multiple users in OFDMA uplink systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7A
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• pp.627-634
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• 2011

In this paper, a new frequency offset estimation method in OFDM system is suggested. To measure fractional part of frequency offset, the repetition feature of cyclic prefix and that of training sequence is adopted. Both method shows relatively large frequency offset estimation error under low SNR circumstances, but this error can be greatly reduced by joint measurement of cyclic prefix and inversely repeated training symbol such as primary advanced preamble (PA-preamble) of IEEE 802.16m IMT-Advanced WiMax system. In this paper, the performance of suggested frequency offset estimation method is verified in IEEE 802.16m IMT Advanced WiMax system, using its PA-preamble and cyclic prefixes of A-preambles.

• The Journal of Engineering Geology
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• v.16 no.4 s.50
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• pp.381-392
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• 2006

The passive surface wave survey using microtremor is conducted in areas of crystalline rock basements to obtain average shear-wave velocity structures to 30 m deep (Vs30), on which the earthquake-resistant design standard is based. Test data were recorded at two sites with triangular and L-shaped arrays for 4 seconds with an sampling interval of 2 ms. The microtremor recorded at a site were analysed using the spatial autocorrelation method to obtain phase-velocity spectra and effects of major factors such as size and shape of away and number of record and receiver were examined. At the other site, shear-wave velocities were derived from VSP and microtremor data separately. The results from these two methods agree to each other reasonably well, indicating that the microtremor method can be an effective geophysical tool to measure Vs30.