Modal processing for acoustic communications in shallow water experiment

Abstract

Acoustical array data from the Shallow Water Acoustics experiment was processed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array designed at the Woods Hole Oceanographic Institution. Phase-shift Keying (PSK) m-sequence modulated signals with different carrier frequencies were transmitted at a distance 19.2km from the array. Even during a strong internal waves activity a low bit error rate was achieved.

Investigation of Mode Filtering as a Preprocessing Method for Shallow-Water Acoustic Communications

“…In this research, a state-limited ML sequence decoder [18] with a short joint finite impulse response (FIR) channel parameters estimator was applied. A joint channel estimation and data recovery algorithm in the form of presurvivor processing [32] was identical to [16], and is briefly described below. Specifically, the method realized the joint minimization of metrics by means of Veterbi trellis algorithm and stochastic approximation, changing channel estimation on each step in the direction opposite to gradient of the metrics.…”

“…A very high-quality data transmission can be achieved for a range of approximately 19.2 km at the frequencies 102 and 203 Hz. Some additional properties of mode filtering for communication, such as constellations of complex envelopes at the output of the mode filters for different modes, were discussed in [16]. The comparison of BER for single hydrophone receiver and for the mode-filtering output is discussed in [17] and is not considered in this paper.…”

“…Results for mode fluctuations in the 2006 Shallow Water Experiment (SW06) were first considered by Duda et al [13], and Collis [15]. The efficiency of mode filtering as a preprocessing method for shallow-water data communications was demonstrated in [16], and was discussed at the 2008 ASA Acoustics Meeting, Paris, France [17].…”

“…The internal wave activity on August 14, 2006 was at a much higher level, which led to strong mode coupling and fluctuations of channel parameters. Another "extremely strong" internal wave solitons activity that occurred on August 19, 2006 was presented in [16]. This case was not typical, as such high level of internal activity was observed only once during SW06.…”

Weakly dispersive modal pulse propagation in the North Pacific Ocean

“…Unlike the present study, those efforts focused on some form of adaptive equalization. We note also that Morozov et al (2008) have previously argued that it may be advantageous to perform mode-processing prior to performing equalization. That suggestion is supported by the results presented here, with the caveat that we recommend focusing on the special class of modal pulses that qualify, approximately at least, as weakly dispersive.…”