• Journal of Integrative Natural Science
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• v.12 no.2
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• pp.35-43
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• 2019

In the content-based image search properties, form information is simple because only the contours of objects are available, and although it can effectively extract the characteristics of the objects, it is sensitive to external noise. The radial distortion, one of these noises, is most prominent in the eyewear and, due to the structural characteristics of the imaging equipment, radiative distortion occurs in almost all imaging equipment. It is very important to determine the similarity of the objects in the images in which these distortions occurred to the actual objects. In order to improve this problem, we propose a strong image search technique for formative noise and radiative distortion using regularization phase angles and moments. Through simulation using Wang DB, the proposed algorithm proved excellent performance for radiation distortion that occurs in general. In addition, a system optimized for database can be implemented by making appropriate changes to the threshold values, enabling image retrieval with the desired level of confidence in various systems. The algorithm proposed in this paper is expected to be utilized as an optimal imaging system by extracting morphological form information of multimedia data.

• 한국전기화학회:학술대회논문집
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• 2000.04a
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• pp.35-35
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• 2000

• Investigative Magnetic Resonance Imaging
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• v.23 no.4
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• pp.328-340
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• 2019

Purpose: To generate phase images with free of motion-induced artifact and susceptibility-induced distortion using 3D radial ultrashort TE (UTE) MRI. Materials and Methods: The field map was theoretically derived by solving Laplace's equation with appropriate boundary conditions, and used to simulate the image distortion in conventional spin-warp MRI. Manufacturer's 3D radial imaging sequence was modified to acquire maximum number of radial spokes in a given time, by removing the spoiler gradient and sampling during both rampup and rampdown gradient. Spoke direction randomly jumps so that a readout gradient acts as a spoiling gradient for the previous spoke. The custom raw data was reconstructed using a homemade image reconstruction software, which is programmed using Python language. The method was applied to a phantom and in-vivo human brain and abdomen. The performance of UTE was compared with 3D GRE for phase mapping. Local phase mapping was compared with T₂* mapping using UTE. Results: The phase map using UTE mimics true field-map, which was theoretically calculated, while that using 3D GRE revealed both motion-induced artifact and geometric distortion. Motion-free imaging is particularly crucial for application of phase mapping for abdomen MRI, which typically requires multiple breathold acquisitions. The air pockets, which are caught within the digestive pathway, induce spatially varying and large background field. T₂* map, that was calculated using UTE data, suffers from non-uniform T₂* value due to this background field, while does not appear in the local phase map of UTE data. Conclusion: Phase map generated using UTE mimicked the true field map even when non-zero susceptibility objects were present. Phase map generated by 3D GRE did not accurately mimic the true field map when non-zero susceptibility objects were present due to the significant field distortion as theoretically calculated. Nonetheless, UTE allows for phase maps to be free of susceptibility-induced distortion without the use of any post-processing protocols.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.2 s.332
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• pp.75-80
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• 2005

In this paper, 2-stage power amplifier has been designed for 5.8GHz wireless LAN application. The power amplifier PldB output power has 21.6dBm at 5.8GHz frequency. Also the power amplifier shows 17.6dB gain and -17.8dB input return loss at 5.725GHz to 5.825GHz. The OFDM modulation and transmission block have been modeled in order to analyse the relationship between the power amplifier distortion and output ACPR for the IEEE 802.11a wireless LAN. The nonlinear characteristic of the power amplifier has been modeled as AM-to-AM and AM-to-PM using the behavioral model, and the output spectrum is analysed with the phase distortion variation. Also, amplifier back-off value from PldB to satisfy the required IEEE 802.11a standard spectrum mask has been simulated with phase distortion, and the simulation data have been compared to the measurement result collected by using the pre-distortion technique.

• Journal of Satellite, Information and Communications
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• v.3 no.2
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• pp.18-25
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• 2008

A major drawback of Orthogonal Frequency Division Multiplexing (OFDM) system is high peak-to-average power ratio (PAPR) of the transmitted signal which introduces inevitable non-linear distortion in the transmission due to the amplifier non-linear property. This causes both in-band distortion and out of band spectrum re-growth. A polynomial based pre-distortion is estimated using the non-linear and inverse non-linear polynomial achieved through the Least Square Error (LSE) method. A new technique of PAPR reduction called 'Phase Realignment' (PR) is proposed which has a optimal effect in improving the BER performance as well as considerable reduction in the PAPR. In this paper we used the PR method along with the 'Peak Clipping' (PC) method is used before the pre-distortion to remove the high peak present in the non constant amplitude of the OFDM signal responsible to drive the amplifier in near saturation region for better performance of the system.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.8
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• pp.867-873
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• 1988

The degradation due to channel distortion in a quadrature modulation system from the ideal constant values over the bandwidth of a direct sequence spread spectrum signal are considered. Through using series expansion for the channel gain and phase response, the degradation in the correlator output at the receiver is found as a function of the parameters involved , including phase error, delay error, linear gin variation, quadratic gain variation, and quadratic phase variation.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1995.10a
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• pp.80-84
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• 1995

ABSTRACT - This paper presents a software based 3 phase 5 level pulse-width modulation(PWM) inverter to reduce total harmonic distortion. The proposed modulation technique can reduce total harmonic distortion and significantly improve the performance of the inverter. In the modulation mode where the frequency ratio is 36 and modulation index is 1.2∼2.0, harmonic components have been mostly eliminated and the magnitude of fundamental component have been maximized by the 3 phase 5 level PWM inverter.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.2
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• pp.169-175
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• 2006

This study investigated variation leakage current maximum value and waveform considering applied voltage phase angel by simulating three environmental conditions, such as fog, salt fog, and kaolin contamination .As the result of applied voltage phase angel characteristics, leakage currents presented almost in phases in the early stage regardless of environmental conditions just after applying the voltage, and the phase of leakage currents certain phase lags for the discharge of the applied voltage when surface discharges occurred due to the continuous environmental contamination. In addition, the difference in phase significantly increased according to the intensity of discharges. The change in distortion rates according to the environmental contamination presented a nearly same level just after applying the voltage. The distortion rate of third harmonic for the fundamental wave presented by the order of fog>salt fog>kaolin when surface discharges occurred due to the applied voltage for certain continued periods. In the case of the fog and salt fog, the scale of spectrums decreased according to the increase in frequencies from the results of the analysis of high frequencies. In addition, the even number frequency presented a relatively large level compared to the odd number frequency under the kaolin contamination.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.3
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• pp.25-32
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• 2004

An advanced algorithm for measurement of phase angle between two sinusoidal signals is proposed in this paper. This algorithm uses discrete sample data of two input signals for calculation of phase angle and amplitude. And the key parameters of the measurement algorithm are described by analytical express, so the calculation of phase angle is simplified. In this paper it is proved that harmonic distortion of the input sinusoidal signals does not affect the measurement value of phase angle by using the proposed algorithm when a whole cycle is sampled. And measurement error by the white Gaussian noise is very small compared by other algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.5
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• pp.1134-1140
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• 2004

In this paper, we investigated the effect of cross phase modulation(XPM) on compensation for WDM channel distortion due to chromatic dispersion, self phase modulation and XPM as a function of fiber dispersion coefficient and modulation format in 320 Gbps WDM systems. The considered WDM transmission system is based on mid-span spectral inversion(MSSI) compensation method, which has highly nonlinear dispersion shifted fiber(HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that the maximum channel input power resulting 1 dB eye opening penalty is reduced due to XPM effect on channel distortion, even if MSSI method was applied to WDM system. But, we confirmed that the effect of XPM on channel distortion becomes decrease as fiber dispersion coefficient of WDM system becomes larger. Futhermore, we confirmed that NRZ is better than RZ as a modulation format for similarly compensating overall WDM channels in WDM system with large fiber dispersion coefficient in order to minimize the effect of the XPM on channel distortion.