• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.296-299
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• 2003

본 논문은 IMT-2000 대역에서 동작하는 피드포워드 증폭기의 선형성 개선을 위한 각 증폭기의 이득 평탄도의 영향에 관한 것이다. 피드포워드 증폭기의 동작 특성을 조사하기 위하여 WCDMA 신호를 인가하여 최종 출력 10W에서 성능을 측정하였다. 특히, 피드포워드 증폭기의 선형성 개선에 영향을 미치는 원인 중, 각 증폭기의 이득 평탄도의 변화에 따르는 선형성의 개선 양에 대하여 조사하였다. 전력 증폭기는 40MHz, 오차 증폭기는 40MHz와 80MHz의 대역에서 이득 평탄도를 변화시키면서 선형성의 개선 양을 조사하였으며, 오프셋 5MHz 지점에서 IMSR을 측정하였다. 측정 결과. 20dB 이상의 개선 효과를 나타내기 위해서는 전력 증폭기는 1.5dB 이내, 오차 증폭기는 0.5dB 이내의 이득 평탄도를 가져야 함을 확인하였으며, 오차 증폭기의 이득 평탄도가 선형성 개선에 더 큰 영향을 미침을 확인하였다.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.62-66
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• 2006

본 논문은 도허티 증폭기 및 포락선 전치 왜곡기를 이용한 전력 증폭기의 효율 및 선형성 개선에 관한 것이다. 전력 증폭기의 효율을 개선하기 위하여 도허티 증폭기를 제작하여 효율 특성을 개선하였으며, 포락선 전치 왜곡기를 이용하여 도허티 증폭기의 선형성 개선량에 대하여 조사하였다. 제작된 도허티 증폭기는 AB 급으로 동작시킨 전력 증폭기와 비교하여 출력 전력 10W에서 8.5%의 효율 개선 효과를 보였으며, 출력 전력 40W에서 12.6%의 효율 개선 특성을 나타내었다. 포락선 전치 왜곡기를 이용한도 허티 증폭기는 출력 전력 10W에서 7dB의 선 형성 개선 효과를 나타내었다. IMT-2000 주파수 대역에서 WCDMA down-link 4 carrier 신호를 이용하여 출력 전력 10W에서 측정한 결과 AB 급으로 동작하는 전력 증폭기와 비교하여 4.2%의 효율 개선 및 6.3dB의 선형성 개선 효과를 나타내었다.

• International Journal of Highway Engineering
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• v.10 no.3
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• pp.33-46
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• 2008

A two-lane highway has a high rate of head-on collisions, sideswipe collisions, crashes with an fixed object. This study was to analyze the weakness of a cross section and a horizontal curve in a two-lane highway and find countermeasures to improve the traffic operations and safety. This study evaluated the effectiveness of widening, curve flattening and superelevation, verified it with a case study and assessed the economical efficiency. This study selected the difference between tangent section operating speeds and curve section operating speeds as an evaluation index of horizontal curve section in a two-lane highway. The results indicated that curve flattening is the best way to improve the traffic safety in a two-lane highway. This study has implication that it provides the quantitative effects of curve flattening. Also directions for future study were discussed.

• Journal of the Korea Society for Simulation
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• v.27 no.2
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• pp.83-90
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• 2018

This paper describes the method of hull shape optimization to improve the resistance performance of planing hulls when a reference hull shape and its principal dimensions are given. First, the planing hull of precedent research is adopted as the reference hull and an optimization problem is formulated by defining hull shape parameters. The search space of this research is discretized for computing cost and DPSO(Discrete binary version of Particle Swarm Optimization) method is used to solve the optimization problem. As the result of optimization, the decrease of resistance is confirmed from the comparison between the reference hull's and the modified hull's planing performance from computational results.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.2
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• pp.75-82
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• 2009

This paper proposes a method which increases the linearity using an improvement mechanism of Doherty power amplifier and compensates the decrement of efficiency due to improvement of linearity. To verify the method, a 20W power amplifier is designed and implemented. Compared with 2-way Doherty power amplifier, the implemented 3-way Doherty power amplifier with class F shows improved linearity about 10dBc and efficiency about 1.5%. Also, efficiency characteristic has been improved about 3.5% compared with the 2-way Doherty power amplifier while maintaining linearity. This results show that the proposed 3-way Doherty power amplifier with class F is shown to be adequate for improvement of efficiency and linearity. It is expected that the proposed amplifier can be used for various wireless communication system amplifiers.

• Journal of Advanced Navigation Technology
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• v.15 no.5
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• pp.789-794
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• 2011

This paper has analyzed the AM-AM and AM-PM characteristics of 7.9 GHz~8.4 GHz X-band TWT used for satellite communication and improved its linearity and IMD performance by using linearizer. The TWT amplifier with the linearizer shows better AM-AM and AM-PM conversion, and has increased 1 dB compression point by 12.3 dB and $2.0^{\circ}/dB$ phase distortion point by 10 dB. The 3rd order intermodulation distortion, IMD3 is measured to be 37.0 dBc that is 16.2 dB improvement at the operating output. This paper also proposed the measurement method of IMD for high power amplifier, and that TWT amplifier can have better linearity and output power by compensating for the AM-PM characteristics.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.59-69
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• 2011

Nonlinear static procedures (NSPs) basing on the concept of performance based seismic design have become one of the promising procedures for seismic evaluation of buildings. Although it needs much less computational cost compared to nonlinear time history analysis (NTHA), its usages are limited to simple structures by its inherent restriction to structures wherein the fundamental mode dominates the response. Several new nonlinear static procedures (Modal Pushover Analysis; MPA and Improved Modal Pushover Analysis; IMPA) which can consider higher modes effect were introduced. Nonetheless, its applicability for complex structures such as cable-stayed bridge has not studied yet. This paper focuses on applicability of nonlinear static procedures for the seismic analysis of cable-stayed bridges. Moreover, reliability indexes which can predict analysis procedure's accuracy are introduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.189-197
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• 2011

OFDM systems are much studied for the recent high speed wireless optical communication system. OFDM system has basically high PAPR and ICI easily generated because of non-linearity and RF impairments. In the wireless optical communication system, optical output power driven by current of LED is not linear so that transmission signals are distorted. Therefore, research about reception performance of this nonlinear optical output emitted by non-linear LED transfer function and OFDM signal has been conducted. Nonlinear effect of LED is different from nonlinear effect of OFDM system in the conventional radio communication system, which degrades the BER performance. In this paper, we apply non-linear transfer function of recently studied LED into OFDM system. So, for reducing the PAPR and suppressing the ICI in frequency domain of receiver, we suggest a new PAPR reduction technique to reduce non-linear distortion of LED and an adaptive ICI suppression algorithm so that BER performance may be improved. Also, the proposed method is verified through simulation results.

• 한국정보통신설비학회:학술대회논문집
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• 2004.08a
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• pp.23-26
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• 2004

본 논문은 전력증폭기의 효율을 개선하기 위한 도허티증폭기의 특성 분석에 관한 것이다. 도허티증폭기의 특성을 분석하기 위해 2-tone신호와 WCDMA신호를 사용하였고 180W PEP LDMOSFET을 사용하였다. 제작된 도허티증폭기는 출력 전력 20W에서 약 10%정도의 효율개선을 나타냈지만 선형성이 저하되는 특성을 나타내었다. 저하된 선형성을 개선시키기 위해 carrier 증폭기(Amp. A)와 peaking 증폭기(Amp. B)를 각각 변화하였으며, carrier 증폭기는 높은 PEP(Peak Envelope Power)와 적은 Id(drain current)가 되도록 하였고, peaking 증폭기는 높은 이득과, 낮은 gate bias에서 IMD(Intermodulation Distortion)가 상쇄되도록 하였다. 최종 측정 결과 출력전력 20W에서 선형성은 class AB증폭기와 비교하여 유사한 결과를 얻었으며, 효율은 약 10% 이상의 개선을 얻을 수 있었다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.4
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• pp.32-42
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• 2010

In this paper, we represent considering parameters for design of a Cartesian vector modulator predistorter to maximize linearity improvement of the predistorter and propose an advanced Cartesian vector modulator predistrotrer with nonlinear starting point control circuit. In order to confirm the performance of the proposed predistorter, the predistorter is applied to power amplifier with 15 W output power for 2.5 GHz band mobile WiMax 1-FA signal. From the measured results, ACLR of -45.3 dBc with 4 dB improvement of ALCR compared with the previous predistorter is obtained and linearity improvement range is also extended.