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

The Korean Institute of Electromagnetic Engineering and Science (한국전자파학회)
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Compensation of OFDM Signal Degraded by Phase Noise and IQ Imbalance

위상 잡음과 직교 불균형이 있는 OFDM 수신 신호의 보상

  • Ryu, Sang-Burm (School of Electrical and Computer Engineering, Chungbuk National University) ;
  • Kim, Sang-Kyun (School of Electrical and Computer Engineering, Chungbuk National University) ;
  • Ryu, Heung-Gyoon (School of Electrical and Computer Engineering, Chungbuk National University)
  • 유상범 (충북대학교 전기전자컴퓨터공학부) ;
  • 김상균 (충북대학교 전기전자컴퓨터공학부) ;
  • 유흥균 (충북대학교 전기전자컴퓨터공학부)
  • Published : 2008.09.30
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Abstract

In the OFDM system, IQ imbalance problem happens at the RF front-end of transceiver, which degrades the BER(bit error rate) performance because it affects the constellation in the received signal. Also, phase noise is generated in the local oscillator of transceivers and it destroys the orthogonality between the subcarriers. Conventional PNS algorithm is effective for phase noise suppression, but it is not useful anymore when there are jointly IQ(In-phase and Quadrature) imbalance and phase noise. Therefore, in this paper, we analyze the effect of IQ imbalance and phase noise generated in the down-conversion of the receiver. Then, we estimate and compensate the IQ imbalance and phase noise at the same time. Compared with the conventional method that IQ imbalance after IFFT is estimated and compensated in front of FFT via the feedback, this proposed method extracts and compensates effect of IQ imbalance after FFT stage. In case IQ imbalance and phase noise exist at the same time, we can decrease complexity because it is needless to use elimination of IQ imbalance in time domain and training sequences and preambles. Also, this method shows that it reduces the ICI and CPE component using adaptive forgetting factor of MMSE after FFT.

OFDM(Orthogonal Frequency Division Multiplexing) 시스템에서 직교 불균형 문제는 송수신기의 front-end에서 발생하며, 성상도에 영향을 주게 되어 BER(Bit Error Rate)을 증가시킨다. 또한, 위상 잡음은 송수신시 국부 발진기에서 발생되는 잡음으로 각 부반송파의 직교성을 깨뜨림으로써 시스템 성능을 크게 저하시킨다. 기존 방식인 PNS(Phase Noise Suppression) 알고리즘은 이러한 위상 잡음을 효과적으로 제거하는 방법이지만 직교 불균형 이동시에 적용되면 오히려 성능이 감소된다. 본 논문에서는 OFDM 시스템의 수신기에서 하향 변환 시 발생하는 직교 불균형과 위상 잡음의 영향을 분석하고, 수신기 FFT(Fast Fourier Transform) 후단에서 파일럿 심볼을 사용하여 CPE를 먼저 제거하고 직교 불균형과 위상 잡음의 성분을 검출하여 등화기의 판정 기준으로 사용하여 보상하는 방법을 제시하였다. 또, 다른 기존 방식들은 FFT 후단에서 추정하고 피드백 시키거나 프리엠블과 같은 시퀀스를 사용하는 방식이지만, 본 논문에서는 FFT 후단에서 MMSE 등화기만을 사용하여 제거하므로 기존의 방법보다 복잡도가 줄어든다. 기존의 위상 잡음 제거 방식에 ICI(Inter Carrier Interference) 제거 기능을 추가하고 직교 불균형 성분을 추출하여 MMSE(Minimum Mean Square Error) 과정 중에 적응 forgetting factor를 적용하면 성능 개선과 직교 불균형 성분의 영향이 줄어들며 성능이 개선됨을 보인다.

Keywords

References

  1. R. Van Nee, R. Prasad, OFDM for Wireless Multimedia Communications, Norwood, MA: Artech House, 2000
  2. Behzad Razavi, RF Microelectronics, NJ: Prentice Hall, 1998
  3. H. G. Ryu, Y. S. Li, "Phase noise analysis of the OFDM communication system by the standard frequency deviation", IEEE Transactions on Consumer Electronics, vol. 49, no. 1, pp. 41-47, Feb. 2003 https://doi.org/10.1109/TCE.2003.1205454
  4. H. G. Ryu, H. S. Lee, "Analysis and minimization of phase noise of the digital hybrid PLL frequency synthesizer", IEEE Transactions on Consumer Electronics, vol. 48, no. 2, May 2002
  5. M. R. Gholami, S. Nader-Esfahani, and A. A. Eftekhar, "A new method of phase noise compensation in OFDM", ICC '03. IEEE International Conference on Communication, vol. 5, pp. 3443-3446, May 2003
  6. Songping Wu, Y. Bar-Ness, "A phase noise suppression algorithm for OFDM-based WLANs", IEEE Communications Letters, vol. 6, Issue. 12, pp. 535- 537, Dec. 2002 https://doi.org/10.1109/LCOMM.2002.806468
  7. Jan Tubbax, Boris Côme, Liesbet Van der Perre, Stéphane Donnay, Marc Engels, Hugo De Man, and Marc Moonen, "Compensation of IQ imbalance and phase noise in OFDM systems", IEEE Transactions on Wireless Communications, vol. 4, no. 3, May 2005
  8. Alireza Tarighat, Ali H. Sayed, "MIMO OFDM receivers for systems with IQ imbalances", IEEE Transactions on Signal Processing, vol. 53, no. 9, Sep. 2005 https://doi.org/10.1109/TSP.2005.847827
  9. A. Schuchert, R. Hasholzner, and P. Antoine, "A novel IQ imbalance compensation scheme for the reception of OFDM signals", IEEE  Transactions on Consumer Electronics, vol. 47, Issue 3, pp. 313- 318, Aug. 2001 https://doi.org/10.1109/30.964115
  10. H. Sari, G. Karam, and I. Jeanclaude, "Transmission techniques for digital terrestrial TV broadcasting", IEEE Communications Magazine, vol. 33, no. 2, pp. 100-109, Feb. 1995
  11. C. L. Liu, "Impacts of I/Q imbalance on QPSK- OFDM-QAM detection", IEEE Transactions on Consumer Electronics, vol. 44, Issue  3, pp. 984-989, Aug. 1998 https://doi.org/10.1109/30.713223
  12. M. Valkama, M. Renfors, and V. Koivunen, "Ad- vanced methods for I/Q imbalance compensation in communication receivers", IEEE Transactions on Signal Processing, vol. 49, no. 10, pp. 2335-2344, Oct. 2001 https://doi.org/10.1109/78.950789
  13. Huseyin Arslan, "IQ gain imbalance measurement for OFDM based wireless communication systems", Military Communications Conference, pp. 1-5, Oct. 2006