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Shallow Water Acoustic Channel Modeling Based on Analytical Second Order Statistics for Moving Transmitter/Receiver | IEEE Journals & Magazine | IEEE Xplore

Shallow Water Acoustic Channel Modeling Based on Analytical Second Order Statistics for Moving Transmitter/Receiver

Publisher: IEEE

Abstract:

Underwater acoustic channels are among the most challenging communication media. Time-varying multipath fading, long delay spread, significant Doppler spread, and frequen...View more

Abstract:

Underwater acoustic channels are among the most challenging communication media. Time-varying multipath fading, long delay spread, significant Doppler spread, and frequency-dependent path loss are the main aspects of such channels. In this paper we present a statistical shallow water channel model for moving transmitter/receiver based on analytical second order statistics. To do so, we first propose a channel impulse response (CIR) model that captures most of the physical properties of shallow waters. Then we find the probability density function (PDF) of the angle of arrival (AoA) for paths with different number of surface and bottom reflections. To find closed form expressions for the second order statistics of the CIR, we approximate the PDFs of AoA with half-circular Rice PDF: a novel PDF introduced in this work. By mathematical tractability of this new PDF, analytical statistics including autocorrelation function, scattering function, and time-frequency correlation function are derived. The results are compared with experimental findings for verification.
Published in: IEEE Transactions on Signal Processing ( Volume: 63, Issue: 10, May 2015)
Page(s): 2533 - 2545
Date of Publication: 06 March 2015

ISSN Information:

Publisher: IEEE

I. Introduction

Underwater wireless networks have applications in many areas such as oceanographic research, oil industry, underwater monitoring, and military systems and are mostly implemented by means of sensors and underwater autonomous vehicles [1]. Operating under the water, these networks are subject to the detrimental effects of acoustic channels that are far more challenging than those of the radio channels. Acoustic propagation is possible only at low frequencies due to the frequency-dependent absorption loss which limits the operating frequency of most underwater systems to below 30 kHz [2]. For example a typical system may have a carrier frequency of 12 kHz modulated by a signal with bandwidth not exceeding 5 kHz [3]. Such a system is considered an ultra-wideband system in the sense that the signal bandwidth is not negligible compared to the carrier frequency. Low propagation speed (1500 m/s) is another issue in underwater communications which leads to channels with delay spreads as long as tens or hundreds of milliseconds that cause strong frequency selectivity. Motion induced Doppler distortions are very extreme in underwater channels due to the low propagation speed, even when the transmitter/receiver are not moving fast. Doppler shifts of tens of Hertz are common and cause great distortions due to the limited available bandwidth. Time-varying multipath fading observed in the radio channels is present also in the acoustic channels and is intensified in shallow waters due to the strong surface and bottom reflections. In spite of these challenges, acoustic waves are the only option for underwater communications since electromagnetic waves cannot propagate over long distances under the water.

References

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