The Journal of Korean Institute of Communications and Information Sciences (한국통신학회논문지)

The Korean Institute of Commucations and Information Sciences (한국통신학회)
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Blind Frequency offset Estimation for Radio Resource Saving in OFDM

OFDM에서 무선자원 절약을 위한 블라인드 주파수 옵셋 추정 방식

  • 전형구 (동의대학교 정보통신과) ;
  • 김경수 (한국전자통신연구원 이동통신연구소)
  • Published : 2009.10.31
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Abstract

In this paper, an efficient blind frequency offset estimation method for radio resource saving in orthogonal frequency division multiplexing (OFDM) systems is proposed. In the proposed method, we obtain two time different received OFDM signal blocks by using the cyclic prefix and define the cost function by using the two OFDM signal blocks. We show that the cost function can be approximately expressed as a closed form cosine function. The approximated cosine function can be obtained from three independent cost function values calculated at three different frequency offsets. In the proposed method, the frequency offset can be estimated by calculating a frequency offset minimizing the approximated cosine function without searching all the frequency offset range. Unlike the conventional methods such as MUSIC method, the accuracy of the proposed method is independent of the searching resolution since the closed form solution exists. The computer simulation shows that the performance of the proposed method is superior to those of the MUSIC and the oversampling method.

본 논문은 orthogonal frequency division multiplexing (OFDM) 통신에서 무선자원을 절약할 수 있는 효율적인 블라인드(blind) 주파수 옵셋 추정 방식을 제안한다. 제안된 방식은 OFDM 통신에서 cyclic prefix (CP)를 이용하여 시간차가 있는 2개의 OFDM 신호 블록을 얻고 이를 이용하여 블라인드 주파수 옵셋 추정을 위한 비용함수를 정의한다. 제안된 방식에서 비용함수는 3개의 독립적인 주파수 옵셋 위치에서 비용함수 값들을 이용하여 폐쇄형(closed form)의 코사인 함수로 나타낼 수 있음을 보인다. 이 코사인 함수를 이용하면 전체 주파수 옵셋 범위에 대한 탐색 없이 최저 비용함수 값을 쉽게 계산할 수 있기 때문에 주파수 옵셋 추정이 효율적이다. 폐쇄형 코사인 함수로부터 구한 주파수 옵셋은 정확도가 해상도에 제한 받지 않기 때문에 signal-to-noise ratio (SNR)이 증가할 수 록 추정 오차가 계속 줄거듦을 확인하였다. 컴퓨터 시뮬레이션 결과 제안된 방식은 기존의 오버샘플링(oversampling)기법이나 MUSIC 방식보다 평균제곱오차 (mean square error, MSE) 성능이 우수함을 보였다.

Keywords

References

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