Clustered pilot tones for carrier frequency offset estimation in OFDM systems

In this paper, we propose a new pilot tone placement scheme and a novel pilot sequence design to estimate the carrier frequency offset (CFO) in OFDM systems. Unlike the conventional approach in which isolated pilot tones are used, we cluster two pilot tones together as a group and these tone groups are equally spaced along the subcarrier axis. The pilot sequence of each group is carefully designed, in which the pilot symbol on the left side in each cluster is made antipodal to the one on the right. The performance in terms of the signal-to-interference ratio (SIR) can be significantly improved by the proposed scheme. Theoretical analysis and simulation results show that the clustered pilot tones can give a substantially lower variance of CFO estimate than that of the isolated pilot tones. For a given CFO, it demonstrates that the variance of the estimate can be reduced by 3 - 14 dB. The bit error rate (BER) is reduced by about 1 dB both in AWGN and multipath fading channels in the simulated cases