• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.4
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• pp.531-538
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• 1998

In this paper the system performance degradation resulting from nonlinear transmitter power amplifier which is essential to increase the efficiency is analysed in a CDMA system. The power amplifier is modeled by its AM-AM, AM-PM characteristics. The effects of power amplifier's nonlinearity such as intersymbol interference, phase distonion 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 Korean Association for Spatial Structures
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• v.10 no.1
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• pp.119-126
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• 2010

The some papers which deal with the dynamic instability for shell-like structures under the dynamic excitation have been published, but there are few papers which treat the essential phenomenon of the dynamic buckling using the phase plane for investigating occurrence of chaos. In nonlinear dynamic, examining the characteristics of attractor on the phase plane and investigating the dynamic buckling process are very important thing for understanding why unstable phenomena are sensitively originated by various initial conditions. In this study, the direct and indirect snapping of shallow EP shell considering geometrical nonlinearity are investigated by Galerkin method numerically. This finding out the characteristic of the dynamic instability through the phases curves and running response spectrum.

• Proceedings of the Optical Society of Korea Conference
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• 1998.08a
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• pp.242-243
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• 1998

• 전기의세계
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• v.14 no.2
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• pp.53-55
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• 1965

본고의 내용은 다음과 같다. 1. 위상측정에 민감한 교직변환기 2. EHV 개폐시험 및 개폐써어지 3. 선형화에 의한 비선형 귀환계의 설계 4. 초도전재료의 응용에 관한 검토

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.46-47
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• 2007

전력시스템안정기는 전력시스템의 저주파 댐핑을 효율적으로 향상시키기 위해 사용되는 제어기이다. 전력시스템안정기의 동적 특성은 위상 보상기의 이득과 시정수와 같은 선형 파라미터와 출력 리미터와 같이 비평활, 비선형 특성을 나타내는 비선형 파라미터에 영향을 받는다. 기존의 선형 제어 방법인 고유치 분석을 통한 선형 파라미터의 최적화 방법은 소신호 동작 범위에 대한 최적화 기법이기 때문에 큰 상정사고 시 효과적인 댐핑 향상을 보장할 수 없게 된다. 이를 극복하기 위하여 하이브리드 시스템에 신경회로망을 임베디드화하여 체계적인 방법으로 비선형 파라미터를 최적화한 후, 고유치 분석을 통해 선형 파라미터를 최적화함으로 전력시스템안정기의 성능 향상을 도모할 수 있다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.6
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• pp.8-15
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• 2003

In this paper, the issue of the differential ring oscillator in designing low phase noise is linearity improvement of delay cell's load resistor. A novel differential delay cell that improves on the Maneatis load is proposed. The linearity improvement of load resistor results in lower phase noise in ring oscillator. For comparison of the phase noise characteristics, Ali Hajimiri's phase noise model is used. In order to have a low ISF(impulse sensitivity function), it is important to have a symmetry between rise time and fall time of oscillation waveform. The ISF value of ing oscillator based on the proposed delay cell is lower than that of the existing ring oscillators. Due to this result, the phase noise is improved by 2~3dBc/Hz for the same power dissipation and oscillation frequency.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.559-567
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• 2012

A level set based topological shape optimization method for nonlinear structure considering hyper-elastic problems is developed. To relieve significant convergence difficulty in topology optimization of nonlinear structure due to inaccurate tangent stiffness which comes from material penalization of whole domain, explicit boundary for exact tangent stiffness is used by taking advantage of level set function for arbitrary boundary shape. For given arbitrary boundary which is represented by level set function, a Delaunay triangulation scheme is used for current structure discretization instead of using implicit fixed grid. The required velocity field in the actual domain to update the level set equation is determined from the descent direction of Lagrangian derived from optimality conditions. The velocity field outside the actual domain is determined through a velocity extension scheme based on the method suggested by Adalsteinsson and Sethian(1999). The topological derivatives are incorporated into the level set based framework to enable to create holes whenever and wherever necessary during the optimization.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.5
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• pp.1073-1078
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• 2012

In this paper, we propose the MEMS system with Duffing equation to confirm nonlinear features in MEMS system. We also analyze nonlinear phenomena when adding the nonlinear term of another type. As a verification, we confirm chaotic motion by parameter variation through the time series, phase portrait and power spectrum.

• Journal of the Korean Institute of Intelligent Systems
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• v.11 no.1
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• pp.22-27
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• 2001

본 논문에서는 복잡한 하이퍼카오스 신호를 발생시키는 HVPM (Hyperchaotic Volume Preserving Maps) 모델의 회로를 제안하고, 보드상에서 구현하고자 한다. 제안한 HVPM 모델은 3차원 이산시간(discrete-time) 연립차분방정식으로 구성되어 있으며, 비선형 사상(maps)과 모듈러(modulus) 함수를 사용하여 랜덤한 카오스 어트랙터(attractor)를 발생시킨다. 이러한 HVPM 모델을 하드웨로 구현하기 위하여 연산 부분은 연산증폭기를 사용하고, 매핑(mapping) 부분은 N형 함수와 비교기를 사용하여 설계한다. 특히, N형의 비선형 함수는 CMOS 전달특성과 선형증폭기의 출력특성을 조합하여 독특하게 구현하였다. 구현한 보드상의 실험에서 카오스 시스템 파라미터 값에 대응하는 가변저항기를 조절하여 비주기적인 하이퍼카오스 신호를 발생시킴을 입증하였다. 또한 출력된 카오스 신호들간의 오실로스코프 사진에서 위상공간(phase space)의 동적응답은 랜덤한 어트랙터를 발생시킴을 확인할 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.738-745
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• 2007

The non-linearity of HPA(high power amplifier) which is an important component in modern communications systems introduces AM/AM and AM/PM distortion so that the transmitted signal is deteriorated. And, the I/Q unbalances and phase error which are generated by non-ideal components are inevitable physical phenomena and lead to performance degradation when we implement a practical two-dimensional (2-D) modulation system. In this paper, we provide an exact and general expression involving the 2-D Gaussian Q-function for the error probabilities of arbitrary 2-D signaling with I/Q amplitude and phase unbalances in nonlinear additive white Gaussian noise (AWGN) channels by using the coordinate rotation and shifting technique.