Frequency Offset Estimation in Coherent Ofdm Systems Using Different Fading Channels

The well known problem in an orthogonal frequency division multiplexing (OFDM) system is its sensitivity to frequency offset. Most of the coherent OFDM systems transmit pilot symbols on some of the subcarriers to estimate channel attenuation and also add a cyclic prefix (CP) to avoid intercarrier interference and intersymbol interference. An estimation algorithm based on the redundancy of both cyclic prefix and pilot subcarriers is proposed for the correction of frequency offset. If the frame timing is synchronised in advance, by considering the two kinds of redundancy simultaneously, the performance of the proposed hybrid algorithm achieves significant improvement under low SNR and short CP. As to high SNR and long CP, the performance of the hybrid algorithm is almost identical to that of CPbased algorithm. Some comparative simulations are given to illustrate the advantages of the proposed hybrid estimation scheme.