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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 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.
Drawbacks • Frequency offset • Local oscillator frequencies • Doppler shift • Result: Loss in Orthogonality • Inter-carrier interference
Frequency offset model • y(n) : received sequence • e: 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 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.