Underwater communications impose greatchallenges due to the unpredictable changes in the environment. In order to accommodate for these changes, equalizers are used to track the Impulse Responses (IRs) andcompensate the intersymbol interference (ISI). Source and array depth shifts are one of the major contributing factors tocontinuous amplitude and phase changes in IR. These changes magnify the problem of data processing in which correlationbetween successive received signals is involved, e.g. passive Time Reversal (pTR) where a probe signal is sent ahead of thedata for post cross-correlation. In this paper, an environment based algorithm is used for pTR equalization, where anappropriate frequency shift of the estimated IR compensates for the geometric changes such as source and array depth shifts. We have applied this Frequency Shift pTR equalizer (FSpTR) on real data collected from Underwater Acoustic Barrier 2007 (UAB’07) sea trial having 1000 baud BPSKsignaling at carrier frequency of 6.25 KHz with a sudden source depth change of 0.5 m at various known instants of time. The results illustrate that a considerable gain can be attained using the environment based equalizer in the presence of source and/or array depth changes. Moreover by closeanalysis of the FSpTR results we have detected surface wave motion through the frequency shifts caused by the array depthvariations.
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