Blind CFO Estimation for Zero-Padded OFDM over Underwater Acoustic Channels

In this paper, we compare the performance and complexity of three existing blind carrier-frequency-offset (CFO) estimators when they are applied to estimate the residual Doppler shift for zero-padded OFDM transmissions over underwater acoustic channels: the null subcarrier based method [1], the O-M algorithm [2], and the Y-G algorithm [3]. Performances of these three methods are evaluated by extensive numerical simulations and by data sets collected from the Mobile Acoustic Communication Experiment conducted off the coast of Martha's Vineyard, MA, July 23, 2010. Simulation results show that the Y-G algorithm always outperforms the O-M algorithm. As far as the fractional part of CFO is concerned, the Y-G algorithm can perform as good as the null subcarrier based method yet with a much lower computational complexity. When working with real data, the Y-G algorithm needs to be modified and integer CFO estimation based on a few null subcarriers is incorporated. Experimental results show that the modified Y-G algorithm, having lower complexity, performs slightly worse than the null subcarrier based method for small and moderate-size constellations, and becomes ineffective for a large constellation.