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 N symbols mapped to bins of IFFT. IFFT bins correspond to the orthogonal sub- carriers.

Baseband OFDM transceiver system

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

Frequency offset model y(n) : received sequence  normalized frequency offset N:number of sub carriers w(n) : complex AWGN

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

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

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

Offset estimation scheme State-Space Model: Recursive steps:

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

References P. H. Moose, “A Technique for Orthogonal Frequency Division Multiplexing Frequency Offset Correction,” IEEE Transactions on Communications, vol. 42, no. 10, October 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 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.

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