• 전자공학회논문지
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• 제53권5호
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• pp.3-12
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• 2016

최근 들어, 밀리미터파 대역을 활용하는 5세대 이동 통신 시스템에 대한 연구가 활발히 진행되고 있으며, 밀리미터파 대역의 전파 감쇠 특성으로 인하여 전력 증폭기의 비선형성을 완화시키는 방법의 중요성이 증가하고 있다. 본 논문에서는 전력 증폭기의 특성을 선형구간과 비선형구간을 구분하여 구간별 계수를 사용하는 구간별 차등 다항식 모델을 제안하였다. 또한, 제안된 모델과 직접 학습 방식을 이용하여 디지털 사전왜곡기 구현 방안을 제시하였다. 제안된 모델의 성능을 검증하기 위하여 LTE 신호를 인가한 60 GHz 대역 전력증폭기를 위한 제안된 모델과 직접 학습 방식에 기반한 디지털 사전왜곡기를 FPGA로 구현하였고 하드웨어 테스트벤치를 통하여 성능 및 연산 복잡도를 비교 검증하였다. 제안된 모델은 기존 단일 다항식 모델 대비 ACLR 측면에서는 3.3 dB 개선됨을 보였으며 연산 복잡도 측면에서는 7.5 % 감소됨을 보여주었다

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.122-127
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• 2003

In this paper, an adaptive predistortion scheme is proposed to compensate nonlinear distortions caused by high power amplifiers (HPA) in OFDM systems. A complex Wiener-Hammerstein model (WHM) is used to describe input-output relationship of HPA with linear dynamics. The predistorter is directly identified by complex power series model with memory, which is an approximate inverse of the HPA expressed by the WHM. The effectiveness of the proposed adaptive compensation scheme is validated by numerical simulation for 64QAM-OFDM systems.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.401-406
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• 2004

In this paper, a new time-domain adaptive predistortion scheme is proposed to compensate for the nonlinearity of high power amplifiers (HPA) in OFDM systems. A complex Wiener-Hammerstein model (WHM) is adopted to describe the input-output relationship of unknown HPA with linear dynamics, and a power series model with memory (PSMWM) is used to approximate the HPA expressed by WHM. By using the PSMWM, the compensation input to HPA is calculated in a real-time manner so that the linearization from the predistorter input to the HPA output can be attained even if the nonlinear input-output relation of HPA is uncertain and changeable. In numerical example, the effectiveness of the proposed method is confirmed and compared with the identification method based on PSMWM.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술대회 논문집 전문대학교육위원
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• pp.31-33
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• 2003

Power amplifier linearity plays a major role in the design of RF communication systems. In this paper, predistortion type linearizer was designed an independently controllable AM/AM and AM/PM predistortion linearizers. This linearizer allows independent adjustment of the AM/AM and AM/PM curves by using two adjustable voltages to compensate the power amplifier non-linearities. The predistortion linearizer was improved the ACPR by 6dB with cdma2000 multi carrier signals. Applying this linearizer to two-tone 880MHz power amplifier, an improvement of adjacent channel leakage power up to 5dBm has been achieved.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.193-196
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• 2001

To reduce third-order intermodulation distortion(IMD3) generated in the down-conversion process of the mixer, predistortion technique was proposed and its performance was verified fDr Cellular band circuit. This method is based on the fact that down converted IMD3 of a down conversion mixer could be canceled by that of predistortor with a fine tuned vector modulator. Two tone test has been performed at 836 Mhz with 442 KHz separation. The results showed that IM3 level was improved about 16dB and PldB of the mixer was increased 3dB. from the above results, the suggested technique is useful to design the down converters for communication system .

• 대한전기학회논문지:시스템및제어부문D
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• 제53권3호
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• pp.188-196
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• 2004

Amplifier linearity plays a major role in the quality of mordern communication systems. The Power amplifier should be operated near saturation region to achieve high efficiency But at this region amplitude and phase distortions of the amplifier remarkably increase with the input power increase and cause a significant adjacent channel interference. In this paper, an independently controllable AM/AM and AM/PM predistortion linearizers consisted of two bias feed resistance linearizers is proposed. This linearizer allows independent adjustment of the AM/AM and AM/PM curves by using two adjustable voltages to compensate tile power amplifier non-linearities. The predistortion linearizer can improve the ACPR by 5.3dB with cdma2000 multi carrier signals. And by applying this linearizer to two-tone(880MHz) power amplifier, third order IMD products are improved up to 8(dB).

• 한국통신학회논문지
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• 제22권4호
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• pp.696-705
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• 1997

This paper presents an efficient adaptive predistortion technique compensating linear and nonlinear distortions caused by high-power amplifier (HPA) with memory in OFDM systems. The efficient adaptive data predistortion techniques proposed for compensation of HPA with memory in single carrier systems cannot be applied to OFDM systems since the possible input levels for HPA is infinite in OFDM systems. Also, previous adaptive predistortion techniques, based on Volterra series modeling, are not suitable for real-time implementation due to high computational burden and slow convergence rate. In the proposed approach, the memoryless HPA preceded by a linear filter in OFDM systems is modeled by the Wiener system which is then precompensated by the proposed adaptive predistorter with a minimum number of filter taps. An adaptive algorithm for adjusting the proposed adaptive predistorter is derived using the stochastic gradient method. It is demonstrated by computer simulation that the performance of OFDM system suffering from nonlinear distortion can be greatly improved by the proposed efficient adaptive predistorter using a small number of filter taps.

• 한국항해학회지
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• 제24권5호
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• pp.417-422
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• 2000

The 3rd order intermodulation(IM3) signals affect a great influence on fundamental signal because IM3 can not be rejected by a filter. To solve this problem, in this paper, a predistortion method was applied. The designed predistorter cascaded to 4 W power amplifier and tested with two-tone spreaded 5 MHz. As an experimental result, it was cleary shown that the 3rd order intermodulation distortion characteristics has been improved as much as 17 dB when the output of the power amplifier is 30.67 dB.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.181-182
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• 2008

In this paper, an cost-effective system architecture is proposed to implement digital predistortion scheme for linearizing the PA amplifing TDD wideband signal. To make digital predistorted signal for compensating nonlinearity of PA, a dedicated ADC and a frequency-down converter are necessary. Proposed scheme is based on the TDD feature that the RF receiver frontend is idle state during the downlink signal processing time and utilize them to make the digital predistorted signal for PA.

• 전자통신동향분석
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• 제18권2호통권80호
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• pp.53-66
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• 2003

고출력 증폭기(HPA)는 위성통신 등 무선통신 시스템의 송신단에서 필수적으로 요구되는 요소 중의 하나이다. 그러나, 대부분의 HPA들은 비선형적인 출력 특성을 가지고 있으므로 이로 인한 신호의 왜곡으로 전송 손실을 야기하게 된다. 이러한 문제점을 해결하기 위하여 HPA를 선형화하는 가장 효율적인 방법으로 제안되어온 것이 사전왜곡(predistortion) 기법이다. 본 고에서는 고출력 증폭기의 비선형성을 보상하기 위한 사전왜곡 방식의 기본 개념과 다양한 사전왜곡 방식에는 어떤한 것들이 있는지 그 기본 원리 및 기술 개발 동향에 관하여 고찰한다.