The Journal of Korean Institute of Electromagnetic Engineering and Science (한국전자파학회논문지)

The Korean Institute of Electromagnetic Engineering and Science (한국전자파학회)
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Adaptive Digital Predistorter Using the NLMS Algorithm for the Nonlinear Compensation of the OFDM Communication System

OFDM통신시스템의 비선형 왜곡 보상을 위한 NLMS 알고리즘 방식의 디지털 적응 전치 왜곡기

  • Kim Sang-Woo (Dept. of Electronic Engineering and Research Institute of Computer, Information & Communication, Chungbuk National University) ;
  • Hieu Nguyen Thanh (Dept. of Electronic Engineering and Research Institute of Computer, Information & Communication, Chungbuk National University) ;
  • Kang Byoung-Moo (Dept. of Electronic Engineering and Research Institute of Computer, Information & Communication, Chungbuk National University) ;
  • Ryu Heung-Gyoon (Dept. of Electronic Engineering and Research Institute of Computer, Information & Communication, Chungbuk National University)
  • 김상우 (충북대학교 전자공학과 및 컴퓨터정보통신연구소) ;
  • ;
  • 강병무 (충북대학교 전자공학과 및 컴퓨터정보통신연구소) ;
  • 유흥근 (충북대학교 전자공학과 및 컴퓨터정보통신연구소)
  • Published : 2005.04.01
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Abstract

In this paper, we propose a pre-distortion method using the NLMS(Normalized Least Mean Square) algorithm to cope with hish PAPR(Peak to Average Power Ratio) problem in OFDM communication system. This proposed scheme estimates the distortion characteristics of HPA, and changes the characteristic against the distortion. Therefore, it can be shown that the adaptive characteristic of the NLMS pre-distorter is good to track the various nonlinear characteristic of HPA, even though HPA characteristic is changed by temperature variation or aging. From the performance analysis, SNR efficiency of NLMS pre-distorter is about $0.5\;\cal{dB}$ less than that of common numerical non-adaptive pre-distorter, when IBO(Input Back Off) is $0\;\cal{dB}$. However, the NLMS pre-distorter is better than the common numerical pre-distorter, because these two pre-distorters have similar performance in higher than $3\;\cal{dB}$ IBO, and the NLMS pre-distorter maintains the constant performance even though characteristic of HPA is changed.

본 논문에서는 OFDM 통신 시스템에서 발생하는 높은 PAPR(Peak to Average Power Ratio) 문제를 해결하기 위해 NLMS(Normalized Least Mean Square) 알고리즘을 이용한 전치왜곡 기법을 제안한다. 제안된 기법은 기본적으로, HPA(High Power Amplifier)치 비선형 왜곡 특성을 추정하고, HPA에 그와 반대되는 특성으로 신호를 변환하여 입력함으로써 비선형 왜곡에 대한 보상이 이루어진다. 뿐만 아니라, NLMS 알고리즘을 통하여 전치 왜곡기의 특성이 자동적으로 갱신되므로 HPA의 비선형 왜곡 특성의 변화에도 그에 맞는 정확한 보상이 이루어질 수 있다. 성능분석 결과, 제안된 NLMS 전치 왜곡기는 IBO(Input Back Off)가 $0\;\cal{dB}$일 경우, 기존의 적응성이 없는 수식적인 전치 왜곡기보다 약 $0.5\;\cal{dB}$의 SNR 손실을 보인다. 하지만 IBO가 $3\;\cal{dB}$ 이상에서 이들의 성능의 거의 같아지며, 제안된 전치 왜곡기는 HPA의 특성 변화에 적응성을 가지므로 실제 시스템에서 기존의 수식적인 전치 왜곡기보다 매우 효과적이라 할 수 있다.

Keywords

References

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