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Ref.: Journal of the Acoustical Society of America, 124(2), pp. 1038-1053, August.
Abstract: Passive time reversal has aroused considerable
interest in underwater communications as a computationally inexpensive
means of mitigating the intersymbol interference introduced by the
channel using a receiver array. In this paper the basic technique is
extended by adaptively weighting sensor contributions to partially
compensate for degraded focusing due to mismatch between the assumed
and actual medium impulse responses. Two algorithms are proposed, one
of which restores constructive interference between sensors, and the
other one minimizes the output residual as in widely-used equalization
schemes. These are compared with plain time reversal and variants that
employ post-equalization and channel tracking. They are shown to
improve the residual error and temporal stability of basic time
reversal with very little added complexity. Results are presented for
data collected in a passive time-reversal experiment that was conducted
during the MREA’04 sea trial. In that experiment a single acoustic
projector generated a 2/4-PSK stream at 200/400 baud, modulated at 3600
Hz, and received at a range of about 2Km on a sparse vertical array
with 8 hydrophones. The data were found to exhibit significant Doppler
scaling, and a resampling-based preprocessing method is also proposed
here to compensate it.