Underwater communications in time-varying sparse channels using passive-phase conjugation

Passive-phase conjugation (PPC) achieves the pulse compression for the time delayed arrivals. This property has been used in underwater acoustic communications. In a time-varying channel, the temporal focusing degrades with time evolution. The block-based approach is implemented to avoid the impact of channel variations. The basic idea is that the channel is assumed constant within each block of a short time interval, and the channel is updated using detected symbols in the previous block. Using real data collected in a recent sea trial, this paper investigates: (1) the communications using PPC processing, where the block-based approach is used, (2) the matching pursuit (MP) algorithm exploiting the channel sparseness. It is found that the MP algorithm improves performance of the communications using PPC processing.