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Journal of Electrical and Computer Engineering
Volume 2012, Article ID 716720, 15 pages
http://dx.doi.org/10.1155/2012/716720
Research Article

Information-Theoretic Analysis of Underwater Acoustic OFDM Systems in Highly Dispersive Channels

1ENSTA Bretagne, UMR CNRS 6285 Lab-STICC, Université Européenne de Bretagne, 2 rue Francois Verny, 29806 Brest Cedex 9, France
2Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115, USA
3Institut Mines-Télécom, Telecom Bretagne, UMR CNRS 6285 Lab-STICC, Université Européenne de Bretagne, Technopôle Brest Iroise-CS 83818, 29238 Brest Cedex, France
4General Sonar Studies Group, Thales Underwater Systems, 525 route des Dolines, 06903 Sophia Antipolis Cedex, France

Received 10 February 2012; Accepted 24 April 2012

Academic Editor: Konstantinos Pelekanakis

Copyright © 2012 Francois-Xavier Socheleau et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This paper investigates the signal-to-interference ratio and the achievable rates of underwater acoustic (UA) OFDM systems over channels where time and frequency dispersion are high enough that (i) neither the transmitter nor the receiver can have a priori knowledge of the channel state information and (ii) intersymbol/intercarrier interference (ISI/ICI) cannot be neglected in the information-theoretic treatment. The goal of this study is to obtain a better understanding of the interplay between interference and the achievable transmission rates. Expressions for these rates take into account the “cross-channels” established by the ISI/ICI and are based on lower bounds on mutual information that assume independent and identically distributed input data symbols. In agreement with recent statistical analyses of experimental shallow-water data, the channel is modeled as a multivariate Rician fading process with a slowly time-varying mean and with potentially correlated scatterers, which is more general than the common wide-sense stationary uncorrelated scattering model. Numerical assessments on real UA channels with spread factors around 10−1 show that reliable OFDM transmissions at 2 to 4 bits/sec/Hz are achievable provided an average signal-to-noise ratio of 15 to 20 dB.