Pilot-aided double-dwell frequency synchronization in OFDM systems

In this paper, a pilot-aided frequency synchronization scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed. A maximum likelihood (ML) estimator based on Double Dwell Synchronization (DDS) is employed for offset estimation and correction. The proposed DDS scheme provides an accurate estimate over a wide estimation range with reduced computational complexity for both AWGN and Rayleigh fading channels. The number of pilot subcarriers as well as the type of used pilot sequence are investigated to improve the system performance. Simulation results show that the proposed DDS provides a reduction of about 3 dB in the required signal-to-noise ratio as the number of pilots is doubled. It is also shown that the DDS approaches the Cramer-Rao Bound (CRB) for systems with large number of subcarriers. Finally, it is shown that for flat fading conditions, using an m-sequence as a pilot sequence provides better performance over complex-valued random or real-valued antipodal sequences.