Abstract
Orthogonal frequency division multiplexed (OFDM) carriers are well studied in literature for their ability to tolerate multipath effects in the presence of ambient noise in an underwater acoustic (UWA) channel. However UWA Doppler destroys the orthogonality of subcarriers, resulting in severely degraded Signal to Noise ratio (SNR). To mitigate this effect, we present a novel method for Doppler estimation and compensation over this channel. This method involves transmitting a training preamble of up to three OFDM symbols. Doppler estimation is carried out based on a sliding window correlation over an OFDM symbol period between the received and local copy of time samples. After rejecting spurious peaks, the correlation values are normalized and existence of Doppler detected when the correlation value exceeds a set threshold. The Doppler shift is then estimated post FFT. Specifically the phase angle of received pilot samples is averaged over three OFDM symbols. This estimated shift is used to compensate the ...
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