Abstract
Underwater acoustic communication by passive-phase conjugation uses a channel probe signal transmitted prior to the data signal in order to estimate the channel response. At the receiver, the received probe signal can be truncated to correlate with the late arrived data signal. In a multipath channel, there are paths that undergo incoherent scattering by the sea surface, and they decrease the coherence between the estimated channel response and the channel response for data signal. For a linear frequency modulation probe signal, a novel processing method is proposed to select time delayed arrivals from the received probe, and this method can also suppress the noise level for the truncated probe signal. Applying this method to the data collected in a sea trial, the communication performance is improved.