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.