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Inter-carrier interference cancellation in OFDM systems

Inter-carrier interference cancellation in OFDM systems. By: Dharamveer Meena Vinodkumar Pralia. Basic OFDM system. Multi-carrier modulation Multiple frequency channels are orthogonal to each other. OFDM modulated signal.

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Inter-carrier interference cancellation in OFDM systems

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  1. Inter-carrier interference cancellation in OFDM systems By: Dharamveer Meena Vinodkumar Pralia

  2. Basic OFDM system • Multi-carrier modulation • Multiple frequency channels are orthogonal to each other.

  3. OFDM modulated signal • N symbols mapped to bins of IFFT. • IFFT bins correspond to the orthogonal sub-carriers.

  4. Baseband OFDM transceiver system

  5. Drawbacks • Frequency offset • Local oscillator frequencies • Doppler shift • Result: Loss in Orthogonality • Inter-carrier interference

  6. Frequency offset model • y(n) : received sequence • e: normalized frequency offset • N:number of sub carriers • w(n) : complex AWGN

  7. Standard OFDM systems • Received signal: • ICI coeffiecient: • Carrier to interference ratio:

  8. Solutions to combat ICI • Self-cancellation scheme • Maximum likelihood estimation • Extended Kalman Filter

  9. Extended Kalman Filtering • A linear approximation of a non linear system Linear : Nonlinear :

  10. Offset estimation scheme • State-Space Model: • Recursive steps:

  11. Offset correction scheme : symbol data QAM - M Restored : received data symbol distorted by frequency offset : estimated normalized frequency offset : number of subcarrier

  12. References • P. H. Moose, “A Technique for Orthogonal Frequency Division Multiplexing Frequency Offset Correction,” IEEE Transactions on Communications, vol. 42, no. 10, October 1994. • J.Armstrong, “Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM,” IEEE Transactions on Communications, vol. 47, no. 3, pp. 365 – 369, March 1999. • C. Muschallik, “Improving an OFDM reception using an adaptive Nyquist windowing,” IEEE Transactions on Consumer Electronics, vol. 42, no. 3, pp. 259 – 269, August 1996.

  13. Thank You

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