Properties of underwater acoustic communication channels in shallow water

Abstract

Underwater acoustic channels are band-limited and reverberant, posing many obstacles to reliable, phase-coherent acoustic communications. While many high frequency communication experiments have been conducted in shallow water, few have carried out systematic studies on the channel properties at a time scale relevant for communications. To aid communication system design, this paper analyzes at-sea data collected in shallow water under various conditions to illustrate how the ocean environments (sea surface waves and random ocean medium) can affect the signal properties. Channel properties studied include amplitude and phase variations, and temporal coherence of individual paths as well as the temporal and spatial coherence of multipaths at different time scales. Reasons for the coherence loss are hypothesized.

Low Frequency Sound Scattering from Rough Bubbly Ocean Surface: Small Perturbation Theory Based on the Reformed Helmholtz-Kirchhoff-Fresnel Method

“…It can be replaced by thin layer reflection coefficient which is designated by R 13 and given as (18) where f 2 is expressed as (19) and k 2 = 2πf/C 2 is the wave number in the middle medium of bubbly water, f is frequency, C 2 is sound speed in bubbly water medium, and z is the mean depth of bubbly water. In Fig.…”

“…In most of these subjects, it is necessary to provide an appropriate acoustic model in order to entail sea surface effects on the entry sound. Active control and acoustic response of structure and fluid interaction [9,10], attenuation and absorption [11], bubble plumes [12][13][14][15], sound transmission [16][17][18], sound propagation in shallow water [19][20][21] and surface waves [22][23] can be considered as important phenomena in the sea.There are different approaches adopted by investigators in order to examine sound scattering from the sea surface. These approaches can be categorized as experimental, theoretical, and numerical studies [24].…”

Optimization of LDPC Codes over the Underwater Acoustic Channel

“…The major difference between the underwater acoustic and radio frequency electromagnetic channels is that the former is characterized by large multipath delays and Doppler dispersion. Most of the difficulties can be attributed to the low speed of sound 1500 m/s in the seawater, which is five orders of magnitude slower than the speed of electromagnetic waves [5,6].…”

Cooperative OFDM Underwater Acoustic Communications with Limited Feedback: Part I

“…The Underwater acoustic (UWA) communication has been regarded as one of the most challenging wireless communications due to its unique channel properties, such as large Doppler shift, dynamic wind-generated bubbles at sea surface, severe multi-path signal propagation [1][2]. Therefore, how to achieve high data rate and reliable communications in fast time-varying UWA environments is a challenging topic that many scientists have put great effort on it [3][4][5].…”