Sensors & Transducers Journal
(ISSN: 2306-8515, e-ISSN 1726-5479)
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0.705
2013 Global Impact Factor |
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205.767
2008 e-Impact Factor |
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Vol. 189, Issue 6, June 2015, pp. 89-96
Abstract:
Underwater communications mainly rely on acoustic propagation which is strongly
affected by frequency-dependent attenuation, shallow water multipath propagation and significant
Doppler spread/shift induced by source-receiver-surface motion. Time-reversal based techniques offer a
low complexity solution to decrease interferences caused by multipath, but a complete equalization
cannot be reached (it saturates when maximize signal to noise ratio) and these techniques in
conventional form are quite sensible to channel variations along the transmission. Acoustic propagation
modeling in high frequency regime can yield physical-based information that is potentially useful to
channel compensation methods as the passive time-reversal (pTR), which is often employed in Digital
Acoustic Underwater Communications (DAUC) systems because of its low computational cost. Aiming to
overcome the difficulties of pTR to solve time-variations in underwater channels, it is intended to insert
physical knowledge from acoustic propagation modeling in the pTR filtering. Investigation is being done
by the authors about the influence of channel physical parameters on propagation of coherent acoustic
signals transmitted through shallow water waveguides and received in a vertical line array of sensors.
Time-variant approach is used, as required to model high frequency acoustic propagation on realistic
scenarios, and applied to a DAUC simulator containing an adaptive passive time-reversal receiver
(ApTR). The understanding about the effects of changes in physical features of the channel over the
propagation can lead to design ApTR filters which could help to improve the communications system
performance. This work presents a short extension and review of the paper 12, which tested Doppler
distortion induced by source-surface motion and ApTR compensation for a DAUC system on a simulated
time-variant channel, in the scope of model-based equalization. Environmental focusing approach in
high frequency underwater acoustics is intended to be explored in future, based on the idea that a set of
oceanic acoustic physical parameters – which are generally estimated in well-known low frequency
matched field processing problems like geoacoustic assessment, ocean tomography and source
localization – could be conveniently used on adaptive filters for channel compensation in DAUC systems.
Keywords: Digital acoustic underwater communications, Passive time reversal, Coherent signaling, Environmental-Based channel compensation, Matched field processing, Time-Variant channel modelling.
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