• Title/Summary/Keyword: Signal distortion

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Analysis of Image Distortion on Magnetic Resonance Diffusion Weighted Imaging

  • Cho, Ah Rang;Lee, Hae Kag;Yoo, Heung Joon;Park, Cheol-Soo
    • Journal of Magnetics
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    • v.20 no.4
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    • pp.381-386
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    • 2015
  • The purpose of this study is to improve diagnostic efficiency of clinical study by setting up guidelines for more precise examination with a comparative analysis of signal intensity and image distortion depending on the location of X axial of object when performing magnetic resonance diffusion weighted imaging (MR DWI) examination. We arranged the self-produced phantom with a 45 mm of interval from the core of 44 regent bottles that have a 16 mm of external diameter and 55 mm of height, and were placed in 4 rows and 11 columns in an acrylic box. We also filled up water and margarine to portrait the fat. We used 3T Skyra and 18 Channel Body array coil. We also obtained the coronal image with the direction of RL (right to left) by using scan slice thinkness 3 mm, slice gap: 0mm, field of view (FOV): $450{\times}450mm^2$, repetition time (TR): 5000 ms, echo time (TE): 73/118 ms, Matrix: $126{\times}126$, slice number: 15, scan time: 9 min 45sec, number of excitations (NEX): 3, phase encoding as a diffusion-weighted imaging parameter. In order to scan, we set b-value to $0s/mm^2$, $400s/mm^2$, and $1,400s/mm^2$, and obtained T2 fat saturation image. Then we did a comparative analysis on the differences between image distortion and signal intensity depending on the location of X axial based on iso-center of patient's table. We used "Image J" as a comparative analysis programme, and used SPSS v18.0 as a statistic programme. There was not much difference between image distortion and signal intensity on fat and water from T2 fat saturation image. But, the average value depends on the location of X axial was statistically significant (p < 0.05). From DWI image, when b-value was 0 and 400, there was no significant difference up to $2^{nd}$ columns right to left from the core of patient's table, however, there was a decline in signal intensity and image distortion from the $3^{rd}$ columns and they started to decrease rapidly at the $4^{th}$ columns. When b-value was 1,400, there was not much difference between the $1^{st}$ row right to left from the core of patient's table, however, image distortion started to appear from the $2^{nd}$ columns with no change in signal intensity, the signal was getting decreased from the $3^{rd}$ columns, and both signal intensity and image distortion started to get decreased rapidly. At this moment, the reagent bottles from outside out of 11 reagent bottles were not verified from the image, and only 9 reagent bottles were verified. However, it was not possible to verify anything from the $5^{th}$ columns. But, the average value depends on the location of X axial was statistically significant. On T2 FS image, there was a significant decline in image distortion and signal intensity over 180mm from the core of patient's table. On diffusion-weighted image, there was a significant decline in image distortion and signal intensity over 90 mm, and they became unverifiable over 180 mm. Therefore, we should make an image that has a diagnostic value from examinations that are hard to locate patient's position.

Performance Evaluation of FC-MMA and RMMA Algorithm for Adaptive Equalization in 2-dimensional QAM Signals (2차원 QAM 신호에서 적응 등화를 위한 FC-MMA와 RMMA 알고리즘의 성능 평가)

  • Lim, Seung-Gag;Kang, Dae-Soo
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.16 no.5
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    • pp.91-97
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    • 2016
  • This paper evaluates the equalization algorithm of FC-MMA (Fast Convergence-Multi Modulus Algorithm) and RMMA (Region based Multi Modulus Algorithm) for the compensation of intersymbol interference which is due to the distortion of communication channel. In order to obtain the error signal for adaptive equalization, the FC-MMA use the modified dispersion constant considering the number of signal symbol, the RMMA separates the 4 region which every symbol points are located, then reduce the symbol point based on this region into constant modulus symbol point. By applying the different principle in order to get the error signal for the updating the tap coefficient of adaptive equalizer, it has the different equalization performance by these error signal. The computer simulation was performed in order to compare the different equalization performance in this paper. The performance index includes the output signal constellation, the residual isi and maximum distortion that is for the convergence characteristics, the SER. As a result of computer simulation, RMMA has more good performance in the residual isi, maximum distortion after in steady state and SER performance than FC-MMA, but not in convergence speed to reach the steady state.

An Adaptive Equalization of Amplitude Chrominance Distortion by using the Variable Step-size Technique

  • Chutchavong, Vanvisa;Janchitrapongvej, Kanok;Benjangkaprasert, Chawalit;Sangaroon, Ornlarp
    • 제어로봇시스템학회:학술대회논문집
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    • 2004.08a
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    • pp.2065-2069
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    • 2004
  • This paper presents an adaptive equalizer using finite impulse response (FIR) filter and least-mean square (LMS) algorithm. Herein, the variable step-size technique (VSLMS) for compensating the amplitude of chrominance signal is utilized. The proposed equalizer can be enhanced and compressed the chrominance signal at color subcarrier. The LMS algorithm employed in simplicity structure but gives slow convergence speed. Thus, the variable step-size is very attractive algorithm due to its computational efficiencies and the speed of convergence is improved. In addition, experimental results are carried out by using the modulated 20T sine squared test signal. It is shown here that the adaptive equalizer can be equalized the amplitude chrominance distortion in color television transmission without relative delay distortion.

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Sound Quality Enhancement in MPEG Surround by Using ILD Distortion (ILD DISTORTION을 이용한 MPEG SURROUND의 음질 개선)

  • Chon, Sang-Bae;Choi, In-Yong;Sung, Koeng-Mo
    • Proceedings of the IEEK Conference
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    • 2006.06a
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    • pp.241-242
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    • 2006
  • MPEG Surround is an audio coding technology that represents multi-channel audio signal with downmixed audio signal(s) and very low bitrate side information based on Binaural Cue Coding. The side information consists of Inter-Channel Level Difference, Inter-Channel Correlation, and payloads. These two parameters are correspondent to the well-known spatial parameters in psycho-acoustics, Inter-aural Level Difference (ILD) and Inter-Aural Cross Correlation (IACC). Though ICLD is to provide perceptually equivalent ILD to the listener, however, the ILD of the original multi-channel audio signal and that of the MPEG Surround encoded signal was different. The difference between two ILD values is defined as ILD Distortion (ILDD). This paper provides how ILDD can be applied to enhance sound quality in MPEG Surround and how much ILDD is decreased.

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Channel Distortion Effects on a BPSK DS/SS and a QPSK DS/SS Signal Demodulation (BPSK DS/SS외 QPSK DS.SS 신호 복호에서 채널 왜곡의 영향)

  • Park, Jin-Soo
    • 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.

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Performance analysis on the nonlinear distortion in OFCDM downlink system using clipped multilevel-PSK (Clipped multilevel-PSK를 이용한 OFCDM 순방향 링크에서 비선형 왜곡에 대한 성능 분석)

  • 안치훈;최영관;장승훈;김동구
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.40 no.11
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    • pp.17-26
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    • 2003
  • To reduce the nonlinear distortion of high power amplifier(HPA) in down link OFCDM system to employ time domain spreading, we apply technology which transmits MPSK(Multilevel-PSK) signal after clipping on multilevel input signal of IFFT subcarrier. In case that the nonlinear distortion of HPA is considered in AWGN channel, performacne of clipping OFCDM system using extended m sequence is over 2.2㏈ better than that of OFCDM system using extended m sequence when the number of user is 8 and 16. In case that the nonlinear distortion of HPA is considered in quasi-static channel, performacne of clipping OFCDM system using extended m code is over 2㏈ better than that of OFCDM system using extended m sequence when the number of user is 8 and 16.

Correction of Single Photon Emission CT Image Distorted by Collimator Characteristic (시준기의 특성으로 인한 SPECT 왜곡 화상의 보정)

  • 백승권
    • Journal of the Institute of Convergence Signal Processing
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    • v.5 no.1
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    • pp.18-24
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    • 2004
  • SPECT technology is used for the reconstructed image in the field of industry noncontact measurement system. One of the distortion problems in reconstructed image quality is a collimator characterictic. The image distortion is caused by a geometrical structure of the collimator. This paper indicated a correction method to remove the image distortion by the structure of the collimator, and compared with the existing correction method. The correction. method removed the image distortion to use deconvolution of projection data with the shift-variant blurring function in the frequency domain. In this pater, I simulated with the collimator angle and distance between the detector and the center of object. and verified with expeimental data. The validity and limitation of correction method is studied for actual industrial applications.

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Suppression of the High Frequency Distortion by Adjustment of Transconductance of the Diode-Connected Transistor in the Current Mode Max Circuit for Multiple Inputs (다수 입력용 전류모드 Max 회로에서 다이오드결선 트랜지스터의 트랜스컨덕턴스 조정에 의한 고주파 왜곡 억제)

  • 이준수;손홍락;김형석
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.40 no.11
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    • pp.37-44
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    • 2003
  • A distortion suppression technology for employing multiple inputs in 3n+1 type current mode Max circuit is proposed using the adjustment of transconductance. If the number of input blocks of the current mode Max circuit increases, the high frequency distortion in the output signal grows. In this paper, it has been disclosed that the distortion in the multiple input Max circuit is proportional to such accumulated parasitic capacitance, to the derivative of the output signal and also to tile inverse of transconductance of the common diode-connected transistor. The proposed idea is by employing as larger transconductance of the common diode-connected transistor as possible. The effectiveness of the proposed idea has been proved through the HSPICE simulation for the current mode Max circuits with various numbers of input signals.

SNR-based Weight Control for the Spatially Preprocessed Speech Distortion Weighted Multi-channel Wiener Filtering (공간 필터와 결합된 음성 왜곡 가중 다채널 위너 필터에서의 신호 대 잡음 비에 의한 가중치 결정 방법)

  • Kim, Gibak
    • Journal of Broadcast Engineering
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    • v.18 no.3
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    • pp.455-462
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    • 2013
  • This paper introduces the Spatially Preprocessed Speech Distortion Weighted Multi-channel Wiener Filter (SP-SDW-MWF) for multi-microphone noise reduction and proposes a method to determine the speech distortion weights. The SP-SDW-MWF is known as a robust noise reduction algorithm against the error caused by the mismatch in microphones. The SP-SDW-MWF adopts weights which determine the amount of noise reduction at the expense of introducing speech distortion in the noise-suppressed speech. In this paper, we use the error of power spectral density between the estimated signal and the desired signal as the evaluation measure. Thus the a priori SNR is used to control the speech distortion weights in the frequency domain. In the experimental results, the proposed method yields better result in terms of MFCC distortion compared to the conventional method.

Partial Principal Component Elimination Method and Extended Temporal Decorrelation Method for the Exclusion of Spontaneous Neuromagnetic Fields in the Multichannel SQUID Magnetoencephalography

  • Kim, Kiwoon;Lee, Yong-Ho;Hyukchan Kwon;Kim, Jin-Mok;Kang, Chan-Seok;Kim, In-Seon;Park, Yong-Ki
    • Progress in Superconductivity
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    • v.4 no.2
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    • pp.114-120
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    • 2003
  • We employed a method eliminating a temporally partial principal component (PC) of multichannel-recorded neuromagnetic fields for excluding spatially correlated noises from event-evoked signals. The noises in magnetoencephalography (MEG) are considered to be mainly spontaneous neuromagnetic fields which are spatially correlated. In conventional MEG experiments, the amplitude of the spontaneous neuromagnetic field is much lager than that of the evoked signal and the synchronized characteristics of the correlated rhythmic noise makes it possible for us to extract the correlation noises from the evoked signal by means of the general PC analysis. However, the whole-time PC of the fields still contains a little projection component of the evoked signal and the elimination of the PC results in the distortion of the evoked signal. Especially, the distortion will not be negligible when the amplitude of the evoked signal is relatively large or when the evoked signals have a spatially-asymmetrical distribution which does not cancel out the corresponding elements of the covariance matrix. In the period of prestimulus, there are only the spontaneous fields and we can find the pure noise PC that is not including the evoked signal. Besides that, we propose a method, called the extended temporal decorrelation method (ETDM), to suppress the distortion of the noise PC from remanent evoked signal components. In this study, we applied the Partial Principal component elimination method (PPCE) and ETDM to simulated signals and the auditory evoked signals that had been obtained with our homemade 37-channel magnetometer-based SQUID system. We demonstrate here that PPCE and ETDM reduce the number of epochs required in averaging to about half of that required in conventional averaging.

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