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The Scientific World Journal
Volume 2016, Article ID 7528353, 11 pages
http://dx.doi.org/10.1155/2016/7528353
Research Article

An Acoustic OFDM System with Symbol-by-Symbol Doppler Compensation for Underwater Communication

1Graduate School of Engineering and Science, University of the Ryukyus, No. 1 Senbaru, Nishihara, Okinawa, Japan
2Department of Information Engineering, University of the Ryukyus, No. 1 Senbaru, Nishihara, Okinawa 9030213, Japan

Received 5 October 2015; Revised 20 January 2016; Accepted 26 January 2016

Academic Editor: Kah Chan Teh

Copyright © 2016 Tran MinhHai 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

We propose an acoustic OFDM system for underwater communication, specifically for vertical link communications such as between a robot in the sea bottom and a mother ship in the surface. The main contributions are (1) estimation of time varying Doppler shift using continual pilots in conjunction with monitoring the drift of Power Delay Profile and (2) symbol-by-symbol Doppler compensation in frequency domain by an ICI matrix representing nonuniform Doppler. In addition, we compare our proposal against a resampling method. Simulation and experimental results confirm that our system outperforms the resampling method when the velocity changes roughly over OFDM symbols. Overall, experimental results taken in Shizuoka, Japan, show our system using 16QAM, and 64QAM achieved a data throughput of 7.5 Kbit/sec with a transmitter moving at maximum 2 m/s, in a complicated trajectory, over 30 m vertically.