ICI Cancellation Based Channel Estimation for OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM), which is a multicarrier modulation scheme, splits high data rate information symbols into lower rate parallel data streams and transmits this parallel information on different orthogonal carriers. The loss of orthogonality among subcarriers causes inter-carrier interference (ICI) which affects both channel estimation and detection of OFDM data symbols. Channel estimation error degrades the performance of coherent receiver limiting capacity, data rate and performance of the overall OFDM system. This paper proposes a novel frequencydomain channel estimator which mitigates the effects of ICI by jointly finding the frequency offset and channel frequency response (CFR). Unlike conventional channel estimation techniques, where ICI is treated as part of the noise, the proposed approach considers the effect of frequency offset in estimation of CFR. A binary search algorithm is used to find the present frequency offset and CFR jointly. Variance of the frequency offset estimator and mean-square error (MSE) performances for conventional least-squares (LS) estimator and the proposed method are obtained using computer simulations. The variance of the jointly estimated frequency offset is found to be very close to the Cràmer-Rao lower bound. It is shown that the proposed method outperforms LS channel estimator especially in ICI dominated situations.