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Blind estimation of the ocean acoustic channel by time-frequency processing

N. Martins
S.M. Jesus
SiPLAB-FCT, Universidade do Algarve,
Campus de Gambelas,
PT-8005-139 Faro, Portugal.

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Ref.: IEEE Journal of Oceanic Engineering, Vol. 31 (3), pp.646-656, 2006.


A time-frequency blind estimator of the ocean acoustic multipath channel response is presented. Both the acoustic channel response and the source input signal are assumed deterministic, and the source signal is assumed highly non-stationary. The estimator relies on the time-frequency representation of the received signal, permitting the separation between the channel and the source signal. First, the unstable initial acoustic arrivals allow the estimation of the source signal instantaneous frequency, by maximization of the radially Gaussian kernel distribution; then, the Wigner-Ville distribution of the received signal is windowed and integrated, where the observation window is defined by the instantaneous frequency estimate, allowing the recovery of the channel impulse response. This last step constitutes an approximation to the conventional matched-filter. Results obtained on a real underwater acoustic data set acquired during the INTIMATE  96 experiment, where the acoustic channel was driven by an LFM signal, show that the channel s detailed structure could be accurately and consistently recovered, with the quality of the channel estimates ranging from 0.796 to 0.973, as compared to the matched-filter result. Time-frequency processing is shown to provide a viable approach to the blind estimation of the ocean acoustic channel excited by a deterministic non-stationary source signal.

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