• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.49-56
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• 2006

In this paper, to overcome the effect of nonlinear power amplifier, CE-CPSK(Constant Envelope Continuous Phase Shift Keying)modulation method which has the constant envelope and continuous phase characteristics is proposed. The code acquisition performances of the CE-CPSK modulated system and BPSK system are analyzed. And the performance is evaluated in terms of mean acquisition time and detection probability with the output backoff of the amplifier in multiuser environment. Results performed in a channel having a high degree of AM nonlinearity(AM-to-AM conversion), have shown that the CE-CPSK signal, when passed through class C-nonlinear Amplifier, has a spectrum with greatly reduced sidelobes compared to the conventional BPSK signal. The code acquisition performance of a CE-CPSK modulation system is better than that of BPSK system with nonlinear amplified multiuser environments.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.2
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• pp.76-80
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• 2007

In this paper, the PAE (Power Added Efficiency) and the linearity of the Doherty amplifier has been improved using dual bias control and PBG (Photonic BandGap) structure. The PBG structure has used to implement on output matching circuit and dual bias control has applied to improve the PAE of the Doherty amplifier at a low input level by applying it to a carrier amplifier. The Doherty amplifier using the proposed structure has improved PAE by 8% and 5dBc of IMD3 (3rd Inter-Modulation Distortion) compared with those of the conventional class AB amplifier. In addition to, it has been evident that the designed the structure has showed more than a 30% increase in PAE for flatness over all input power level.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1367-1377
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• 2001

고전력 증폭기의 비선형성, 수신 주파수 편차 및 심볼 타이밍 편차가 모두 존재하는 실제 IEEE 802.11a 무선 LNA 시스템의 성능을 분석하였다. 이러한 시스템에서 데이터가 OFDM 변조된 후 주파수 선택적 Rayleigh 페이딩 채널을 통하여 전송될 때의 비트 오류율을 구하였다. 증폭기의 최대 출력 전력 대 평균 출력 전력비가 6dB이며 주파수 편차가 0.01이고 심볼 타이밍 편차가 2 샘플링 주기 시간인 경우에, 이 무선 LAN 시스템에서 10-5의 비트 오류율을 얻기 위하여 필요한 $E_{b}$ /$N_{o}$ 의 크기는 대략 20~24dB로 분석되었다. 이와 같은 실제 시스템과 정확한 채널 추정, 선형 증폭기, 정확한 주파수 동기 및 심볼 동기 가정의 이상적인 시스템간의 성능을 비교한 결과, 같은 크기의 비트 오류율을 얻기 위하여 이 실제 시스템에서 대략 1~3dB 정도의 $E_{b}$ /$N_{o}$ 가 더 소요된다.

• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.256-262
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• 2006

This paper proposes a new predistortion linearizer to compensate for AM/AM and AM/PM in the nonlinear characteristics of amplifier. This consists of common-emitter amplifier and schottky diode that is connected between emitter and ground. When effective resistance of the schottky diode with bias condition varies, common-emitter amplifier with series feedback has a increase of amplitude and expansion of phase. This makes a amplifier nonlinear characteristics are to be improved. The proposed linearizer and amplifier has been manufactured and tested to operate in cellular base station frequency (869~894MHz). The test results show that third order intermodulation distortion (IMD3) cab be removed by more than 10.4dB in case of CW 2-tone signals ${\Delta}f$=1MHz, and the adjacent channel power ratio (ACPR) also can be improved by more than 9.6dB for CDMA IS-95 1FA signals.

• Journal of IKEEE
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• v.4 no.2 s.7
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• pp.241-248
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• 2000

A linear power amplifier is particular emphasized on the CDMA system using a linear modulation scheme, because intermodulation distortion which cause adjacent channel interference and co channel interference is mostly generated in a nonlinear power amplifier. In this paper, a new type of linearization technique proposed. It is presented that balanced MESFET predistortion linearizer added. Experimental result are present for Korea PCS(Personal Communication Service) frequency band. The implemented linearizer is applied to a 30dBm class A power amplifier for simulation Performance. The predistortion linearizer improves the 1dB compression point of the HPA about 2dBm, and intermoudulation distortion about 12.5dBc.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2016.11a
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• pp.60-62
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• 2016

이동통신 시스템의 OFDM(Othogonal frequency division multiplexing) 신호는 큰 PAPR(Peak to Average Power Ratio)을 가지기 때문에 비선형 특성을 가지는 전력 증폭기의 효율 감소를 가져온다. 이러한 전력 증폭기의 비선형 특성을 개선하여 효율을 증가시키기 위해서 전력 증폭기의 역 특성을 가지는 디지털 전치 왜곡기가 이용된다. 본 논문에서는 제곱근 근사를 이용한 Look-up Table(LUT) 기반의 디지털 전치왜곡(Digital Pre-Distortion :DPD) 기법을 제안한다. 제안하는 방식은 복소 이득(Complex Gain) LUT 구조에서 입력신호의 크기를 구할 때, 기존의 테이블을 이용하여 제곱근 연산을 하는 방식보다 좋은 성능을 내면서 근사를 위한 테이블의 메모리를 필요로 하지 않는다. 또한 간단한 쉬프트 연산 등을 이용하므로 DSP 또는 MCU 기반의 DPD를 구현할 때 간단하게 구현 될 수 있다는 장점을 갖는다. 컴퓨터 모의실험을 통해 제안하는 제곱근 근사방식을 이용한 DPD와 기존의 방식을 사용한 DPD를 비교함으로써 제안하는 방식이 기존 방식보다 좋은 성능을 내면서도 보다 효율적으로 구현될 수 있음을 검증하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.50-54
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• 2011

In this article, the linearity of single power amplifier is improved by suppress $2^{nd}$ and $3^{rd}$ harmonics at output port of high power amplifier and by cancelling of $3^{rd}$ IMD. The matching network in order to suppress harmonics consists of metamaterial like the CRLH. The $2^{nd}$ and $3^{rd}$ harmonics are suppressed over 27 dBc, respectively. A phase of generated $3^{rd}$ IMD at output of DPA (drive power amplifier) has changed in order to offset the $3^{rd}$ IMD of HPA (high power amplifier). The harmonics of the proposed PAM suppress over 6 dB than single HPA. The PAM has a 36.98 dBm of the output power, 21.6 dB of the power gain and 29.4 % of the PAE. The harmonics is a -53 dBc about PAM. This result indicate that a harmonic level is lower 20 dB than reference power amplifier.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.160-163
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• 2009

HPA is one of the most essential device in wireless communication systems. However, because of nonlinear characteristic of HPA transmit signal is distorted with both amplitude and phase, this distortion leads to deepening adjacent channel interference. So a technique to change the nonlinear characteristic with linear characteristic is needed. In this paper, Among all techniques, we adopts a polynomial pre-distortion technique. Pre-distorted signal by pre-distorter has opposite characteristic with HPA. In result, the signal passed through pre-distorter and HPA has linear characteristic. But the accuracy of opposite characteristic of HPA is decreased at near portion of saturation point. So we improve the accuracy of opposite characteristic of HPA by using PAPR reduction method. In this paper, an adaptive polynomial pre-distortion technique is introduced to counterbalance the nonlinear characteristic of the transmit power amplifier, and a PAPR reduction method is introduced to increase efficiency of polynomial pre-distorter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4A
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• pp.197-204
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• 2012

We propose a new scheme combining the compensation of HPA nonlinearity and the calibration of the path imperfections in the downlink OFDM smart antenna systems. We use a two term third-order polynomial (without second-order term) and the feedforward method for compensation and calibration to make each path of the antenna array have equal characteristics. Since the proposed scheme does not alter the base-band signal, it can be applied to the smart antenna system independently of the base-band signal processing section. The result of computer simulations shows that, with the addition of only one third-order term, the adverse nonlinear effects can be effectively compensated, and the those of linear imperfections can be calibrated as well.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1086-1093
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• 2001

A new linearization technique for RF high-power amplifiers(HPAs) using n-th order error signal generator (ESGn) is proposed. The n-th order ESG generates an error signal based on the complex envelope transfer characteristics of the HPA, which is combined at the output of the HPA. Therefore, the higher-order nonlinearlities are not affected by the ESG$\_$n/ and the stability of the linearized system is guaranteed due to the inherent open-loop configuration. Moreover, the output delay loss can be avoided, because the error signal is generated with the input signal of the HPA. The IMD(intermodulation distortion) improvement obtained applying the ESG$\_$7/ to 5 W class A HPA in cellular band demonstrates the feasibility of the proposed postdistortion system.