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

Abstract

Abstract-Acoustical array data from the 2006 Shallow Water Experiment (SW06) was analyzed 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, which spans the water column from 12-m depth to the bottom in shallow water 80 m in depth. Binary -sequence data were used to phase-shift-keyed (PSK) modulate signals with different carrier frequencies. No error correction coding was used. The received signals were processed by a system that does not use training or pilot signals. Signals received both during periods of ordinary internal wave activity and during a period with unusually strong internal wave solitons were processed and analyzed. Different broadband mode-filtering methods were analyzed and tested. Broadband mode filtering decomposed the received signal into a number of independent signals with a reduced delay spread. The analysis of signals from the output of mode filters shows that even a simple demodulator can achieve a low bit error rate (BER) at a distance 19.2 km.Index Terms-Signal processing, underwater acoustic arrays, underwater acoustic communications.

A Survey of Underwater Acoustic Communication and Networking Techniques

“…In the current researches, coherent OFDM method has been considered as the most appropriate method for UWAC. However, in addition to OFDM mo feasibility study on the decomposition of normal mode as a preprocessing step in UWAC has been investigated by Morozov et al (2010). Same like multicarrier modulation this method is also based on shortening of channel delay spread to mitigate the effect of ISI and channel induced fluctuation by rapid adaptation.…”

Symbol Estimation Algorithm for MIMO Underwater Acoustic Communication System Based on Multiplicative Noise Model

“…In addition, the complex multipath propagation and time-frequency selective fading are prone to causing serious distortion of UWA communication signals, which set obstacles to the high-speed and reliable transmission of UWA communication. Hence, how to characterize the underwater channel and estimate the transmitted symbol have become the focus of current research [1][2][3][4].…”

Full reconstruction of acoustic wavefields by means of pointwise measurements

“…It is of the especial importance in inverse problems where even tiny features of an interference pattern might give information about medium passed by a wave, or information about properties of a wave source. In the context of underwater acoustics, it allows for straightforward extraction of wavefield constituents corresponding to individual modes [1], [2], [3], [4], [5], rays [6], and the so-called stable components being Gaussian wavepackets with minimal uncertainty [7]. Expansion of a wavefield over individual modal contributions can be used, for example, for long-range environment reconstruction using mode-based schemes of hydroacoustical tomography [8], [9], [10], [11].…”

“…Also, detailed analysis of a wavefield structure is helpful for robust identification of propagation geometry, that is of great importance for geoacoustic inversion [12] and seismic surveys [13], [14], as well as for various kinds of the matched field processing [15], [16], [17]. Development of receiving-transmitting arrays allowing for full and accurate reconstruction is important in the context of applications associated with sound focusing, like underwater communication [4], [18] and remote monitoring of the ocean bottom [19], [20]. Detailed information about a wavefield structure facilitates experimental investigation of scattering physics [21], [22], [23], [24], [25], [26], especially in the context of wave chaos [27], [28], [29], [30], [31], [32].…”