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Publication
Environmental model-based time-reversal underwater communications
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| 16.11 MB | Adobe PDF |
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Advisor(s)
Abstract(s)
Advances in underwater acoustic communications require the development of methods to
accurately compensate channels that are prone to severe double spreading of time-varying
multipath propagation, fading and signal phase variations. Assuming the environmental
information as a key issue, this work aims to improve communications performance
of single-input-multiple-output transmission systems in such channels through the enhancement
of their estimates used for equalization. The acoustic propagation physical
parameters of the environment between the source and the receivers are considered in
the process. The approach is to mitigate noise e ects in channel identi cation for Passive
Time-Reversal (PTR), which is a low complexity probe-based refocusing technique to
reduce time spreading and inter-symbol interference. The method Environmental-based
PTR (EPTR) is proposed that, inspired by matched eld inversion, inserts physics of
acoustic propagation in the channel compensation procedure through ray trace modeling
and environmental focalization processing. The focalization is the process of tweaking
the environmental parameters to obtain a noise-free numerical model generated channel
response that best matches the observed data. The EPTR performance is tested and
compared to the pulse-compressed PTR and to the regularized `1-norm PTR. The former
is based on classical `2-norm channel estimation and the latter, inspired by compressive
sensing, uses weighted `1-norm into the `2-norm estimation problem to obtain improved
estimates of sparse channels. Successful experimental results were obtained with the proposed
method for signals containing image messages transmitted at 4 kbit/s from a source
to a 16-hydrophones vertical array at 890 m range during the UAN'11 experiment conducted
o the coast of Trondheim (Norway). The scienti c contributions of this work are
(i) the understanding of the process of employing physical modeling and environmental
focalization to equalize and retrieve received messages in underwater acoustic communications,
thus exploiting the sensitivity of environmental parameters in order to adapt a
communications system to the scenario where it is used; and (ii) the presentation of a new
PTR-based method that focuses environmental parameters to model suitable noise-free
channel responses for equalization and whose real data results were successful for a set
of coherent signals collected at sea. The proposed method is a step forward to a better
understanding on how to insert physical knowledge of the environment for equalization in
digital underwater acoustic communications.
Description
Keywords
Comunicações submarinas Processamento de tempo-reverso Equalização Comunicações coerentes Modelos físicos de propagação Focalização ambiental