• Electronics and Telecommunications Trends
• /
• v.10 no.4 s.38
• /
• pp.129-142
• /
• 1995

본 고에서는, 음성을 디지털로 부호화하여 전송함으로써 발생되는 신호 대 양자화왜곡 비(Q)의 개념 및 CODEC과의 관계를 분석하고, MNRU를 디지털 회로로 구현하는데 필요한 입력음성 신호레벨, 잡음의 통계적 성질 및 진폭제한이 음성품질에 미치는 영향을 살펴보았다. 또한, 본 연구에서 구현한 MNRU의 성능에 대해 주관평가 실험을 실시하여, 다른 나라의 주관평가 결과와 비교/분석하였다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.6C
• /
• pp.580-593
• /
• 2003

A joint design scheme has been proposed to optimize the source encoder and the modulation signal constellation based on the minimization of the end-to-end distortion including both the quantization error and channel distortion. The proposed scheme first optimizes the VQ codebook for a fixed modulation signal set, and then the modulation signals for the fixed VQ codebook. These two steps are iteratively repeated until they reach a local optimum solution. It has been shown that the performance of the proposed system can be enhanced by employing a new efficient mapping scheme between codevectors and modulation signals. Simulation results show that a jointly optimized system based on the proposed algorithms outperforms the conventional system based on a conventional QAM modulation signal set and the VQ codebook designed for a noiseless channel.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.2
• /
• pp.65-70
• /
• 2004

This paper presents a novel linearization scheme for a nonlinear RF amplifier It is based on the amplitude modulation with envelope signal. The 3rd order distortion generator is composed of two FETs and it adopts a balanced structure for the purpose of main carrier cancellation. The amplitude and phase of the IM3 component can be controlled at RF band. This predistorter is implemented and tested at the KOREA PCS Tx. band (1840∼1870MHz). Experimental results of two-tone test show that the IM3 cancellation is achieved about 30-40 ㏈ for the wide dynamic range. The adjacent channel power ratio is improved by over 10 ㏈ at the broad-band CDMA signal with a peak to average power ratio of l0㏈, and this improvement is maintained through a wide range of output power levels.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.4
• /
• pp.65-71
• /
• 2007

Doherty amplifier has more efficiency and distortion than general amplifier. These distortion classified amplitude distortion and phase distortion, memory effect distortion. This paper reports on an attempt to investigate, model and quantity the contribution of the electrical nonlinearity effects and the thermal memory effects to a doherty amplifier's distortion generation and suggests thermal memory effect compensator for pre-distorter. Also this paper reports on the development of an accurate dynamic expression of the instantaneous junction temperature as a function of the instantaneous dissipated power. The parameters of suggested model suppress thermal memory effects doherty amplifier with pre-distorter. Pre-distorter with electrothermal memory effect compensator for doherty amplifier enhanced ACLR performance about 22 dB than general doherty amplifier. Experiment results were mesured by 50W LDMOS Doherty amplifier and pre-distorter with electrothermal memory effect compensator was simulated by ADS.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.37 no.1
• /
• pp.1-11
• /
• 2000

We propose a predistorter to compensate for nolinear distortion induced by a high power amplifier employed in multi carrier-code division multiple access (MC-CDMA) systems. The proposed scheme rests upon the fixed point iteration (FPI) associated with the contraction mapping theorem. Unlike the predistorter based on the FPI already presented by the authors in other literatures which operates on complex-valued modulation signals, the proposed predistorter in this paper deals with real-valued FPI on modulation signal amplitudes, resulting in less complexity. Simulation results on a BPSK-modulated, 64-subcarrier synchronous MC-CDMA baseband system with a traveling wave tube amplifier in the transmitter, indicate that the proposed predistorter achieves significant improvement in terms of bit error rate and total degradation over those without the predistorter. Moreover, the proposed predistorter outperforms the complex-valued counterpart, in particular, for small output back-off levels.

• Progress in Medical Physics
• /
• v.23 no.3
• /
• pp.145-153
• /
• 2012

In this study, we quantify the residual motion artifact in 4D-CT scan using the dynamic lung phantom which could simulate respiratory target motion and suggest a simple one-dimension theoretical model to explain and characterize the source of motion artifacts in 4DCT scanning. We set-up regular 1D sine motion and adjusted three level of amplitude (10, 20, 30 mm) with fixed period (4s). The 4DCT scans are acquired in helical mode and phase information provided by the belt type respiratory monitoring system. The images were sorted into ten phase bins ranging from 0% to 90%. The reconstructed images were subsequently imported into the Treatment Planning System (CorePLAN, SC&J) for target delineation using a fixed contour window and dimensions of the three targets are measured along the direction of motion. Target dimension of each phase image have same changing trend. The error is minimum at 50% phase in all case (10, 20, 30 mm) and we found that ${\Delta}S$ (target dimension change) of 10, 20 and 30 mm amplitude were 0 (0%), 0.1 (5%), 0.1 (5%) cm respectively compare to the static image of target diameter (2 cm). while the error is maximum at 30% and 80% phase ${\Delta}S$ of 10, 20 and 30 mm amplitude were 0.2 (10%), 0.7 (35%), 0.9 (45%) cm respectively. Based on these result, we try to analysis the residual motion artifact in 4D-CT scan using a simple one-dimension theoretical model and also we developed a simulation program. Our results explain the effect of residual motion on each phase target displacement and also shown that residual motion artifact was affected that the target velocity at each phase. In this study, we focus on provides a more intuitive understanding about the residual motion artifact and try to explain the relationship motion parameters of the scanner, treatment couch and tumor. In conclusion, our results could help to decide the appropriate reconstruction phase and CT parameters which reduce the residual motion artifact in 4DCT.

• KIPS Transactions on Software and Data Engineering
• /
• v.4 no.9
• /
• pp.377-384
• /
• 2015

In this paper we propose a visualization tool for distortion-free time-series matching. Supporting distortion-free is a very important factor in time-series matching to get more accurate matching results. In this paper, we visualize the result of time-series matching, which removes various time-series distortions such as noise, offset translation, amplitude scaling, and linear trend by using moving average, normalization, linear detrending transformations, respectively. The proposed visualization tool works as a client-server model. The client sends a user-selected time-series, of which distortions are removed, to the server and visualizes the matching results. The server efficiently performs the distortion-free time-series matching on the multi-dimensional R*-tree index. By visualizing the matching result as five different charts, we can more easily and more intuitively understand the matching result.

• Journal of Satellite, Information and Communications
• /
• v.3 no.1
• /
• pp.15-21
• /
• 2008

The high peak to average power ratio (PAPR) of OFDM (Orthogonal Frequency Division Multiplexing) system 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. In this paper we tried to compensate the problem by using polynomial based pre-distortion. Estimation of both the non-linear and inverse non-linear polynomial is achieved using the Least Square Error (LSE) method. Using these parameters closed form pre-distorter can be easily created. We also used the 'partial peak cancellation and clipping' method 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 Korea Institute of Information and Communication Engineering
• /
• v.14 no.5
• /
• pp.1078-1084
• /
• 2010

This paper presents a speech enhancement system which restores the amplitude components and phase components by discrete Fourier transform (DFT), using neural network training by back-propagation algorithm. First, a neural network is trained using DFT amplitude components and phase components of noisy speech signal, then the proposed system enhances speech signals that are degraded by white noise using a neural network. Experimental results demonstrate that speech signals degraded by white noise are enhanced by the proposed system using the neural network, whose inputs are DFT amplitude components and phase components. Based on measuring spectral distortion measurement, experiments confirm that the proposed system is effective for white noise.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.11
• /
• pp.1677-1688
• /
• 1993

Two dimensional amplitude scrambling algorithm using the hopping filter, which improve the drawback of conventional speech encryption scheme, is powerful encryption scheme in analog sppech signal. In this paper, we proposed the variable delay weight algorithm using hopping filter in order to solve the synchronization problem of two dimensional amplitude scrambling. Futhermore, analyzing the distortion of received signal which is transmitted in the gaussian noise channel, we determined the optimal encryption algorithm and optimal SNR using the simulation.