The Journal of the Institute of Internet, Broadcasting and Communication (한국인터넷방송통신학회논문지)

The Institute of Internet, Broadcasting and Communication (한국인터넷방송통신학회)
권호 표지
DOI QR코드

DOI QR Code

Convergence Speed Improvement in MMA Algorithm by Serial Connection of Two Stage Adaptive Equalizer

2단 적응 등화기의 직렬 연결에 의한 MMA 알고리즘의 수렴 속도 개선

  • Lim, Seung-Gag (Dept. of Information and Communication, Kongju National University)
  • 임승각 (공주대학교 정보통신공학전공)
  • Received : 2015.03.03
  • Accepted : 2015.06.12
  • Published : 2015.06.30
Download PDF
⟨ Previous Next ⟩

Abstract

This paper deals with the mMMA (modified MMA) which possible to improving the convergence speed that employing the serial connecting form of two stage digital filter instead of signal filter of MMA adaptive equalizer without applying the variable step size for compensates the intersymbol interference by channel distortion in the nonconstant modulus signal. The adaptive equalizer can be implemented by signal digital filter using the finite order tap delay line. In this paper, the equalizer is implemented by the two stage serial form and the filter coefficient are updated by the error signal using the same algorithm of MMA in each stage. The fast convergence speed is determined in the first stage, and the residual isi left at the output of first stage output is minimized in the second stage filter. The same digital filter length was considered in single stage and two stage system and the performance of these systems were compared. The performance index includes the output signal constellation, the residual isi and maximum distortion, MSE that is measure of the convergence characteristics, the SER. As a result of computer simulation, mMMA that has a FIR structure of two stage, has more good performance in every performance index except the constellation diagram due to equalization noise and improves the convergence speed about 1.5~1.8 time than the present MMA that has a FIR structure of single stage.

본 논문에서는 nonconstant modulus 신호를 대상으로 채널의 찌그러짐에 의한 부호간 간섭을 보상하기 위한 MMA (Multiple Modulus Algorithm) 적응 등화기를 가변 적응 스텝 크기를 적용하지 않고 2단의 직렬 연결 형태로 구현하여 수렴 속도를 개선할 수 있는 mMMA (modified MMA)에 대하여 다룬다. 적응 등화기는 유한 차수의 탭 지연선에 의한 단일 디지털 필터로 구현되므로, 논문에서는 이를 2단의 직렬 연결 필터로 구현한 후 각 단에서는 MMA와 동일한 알고리즘으로 오차 신호를 얻은 후 필터 계수를 갱신하게 된다. 따라서 첫단에는 빠른 수렴 속도를 결정하며, 두 번째단에서는 첫단의 출력에 포함되어 있는 잔류 isi양을 최소화시키도록 탭 계수를 갱신한다. 이때 1단 시스템과 2단 시스템은 동일한 차수의 필터가 되도록 조정하면서 적응 등화 성능을 비교하였으며, 성능 비교를 위한 지수로는 등화기 출력 신호 성상도, 수렴 특성을 나타내는 잔류 isi, 최대 찌그러짐과 MSE, 채널의 신호대 잡음비에 따른 SER을 사용하였다. 시뮬레이션 결과 2단의 FIR 구조를 갖는 mMMA가 1단의 기존 MMA보다 등화 잡음에 의한 성상도를 제외한 모든 성능 지수에서 우월하며, 수렴 속도는 1.5~1.8배 정도 개선됨을 확인하였다.

Keywords

References

  1. J.Yang, J.J.Werner, G.A.Dumont,"The Multimodulus Blind Equalization and Its Generalized Algorithms", IEEE Journal on S.A.C., Vol.20, No.3, pp.997-1015, June 2002.
  2. S.Abrar, R.A.Axford, "Sliced Multi-modulus Blind Equalization Algorithm", ETRI Jorunal, Vol.27, No.3, pp.257-266, June 2005. https://doi.org/10.4218/etrij.05.0104.0027
  3. M.Abide D., A. Ozen, "A Novel Variable Step Size Adjustment Method Based on Autocorrelation of Error Signal for the Constant Modulus Blind Equalization Algorithm", Radio Engineering, Vol.21, No.1, pp.37-45, April 2012.
  4. M.Pinchas, "Two Blind Adaptive Equalizers Connected in Series for Equalization Performance Improvement", Jour. of Signal and Information Processing, pp.64-71, April 2013.
  5. O.Shalvi, E.Weinstein, "New Criteria for Blind Deconvolution of Nonminimum Phase Systems (Channel)", IEEE Trans. on Information Theory, Vol.36, No.2, pp.312-321, 1990. https://doi.org/10.1109/18.52478
  6. M.Lazaro, I.Santamaria, D.Erdogmus et. al., "Stochastic Blind Equalization Based on pdf Fitting Using Parzen Estimator", IEEE Trans. on Signal Processing, Vol.53, No.2, pp.696-704, 2005. https://doi.org/10.1109/TSP.2004.840767
  7. D.S.Kang, S.G.Lim, "The Performance Comparison of MMA and S-MMA Adaptive Equalization Algorithm for QAM Signal", Jour. on I.W.I.T., Vol.13, No.1, pp. 19-26, Feb. 2013.
  8. K.N.Oh, "An Algorithm for Variable Step-Size Improving Steady-State Performance of Blind Equalization", Jour. of K.I.I.T., Vol. 9, No. 10, pp.43-48, Oct. 2011