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Plenary Talk 1
Signal Processing for Underwater Communications
Milica Stojanovic
Northeastern University
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Monday, June 22nd
10:15 - 11:15
Teatro del Pavone
Abstract
Wireless information transmission through the ocean is one of the enabling technologies for the development of future ocean-observation systems, whose applications range from oil industry to aquaculture and include gathering of oceanographic data, pollution control, climate recording, prediction of natural disturbances, detection of objects on the ocean floor, and transmission of images from remote sites. Implicitly, wireless signal transmission is crucial for control of autonomous underwater vehicles which will serve as mobile nodes in the future information networks of distributed underwater sensors. The ability to communicate wirelessly provides advantages of collecting data without the need to retrieve the instruments, and maneuvering underwater vehicles and robots without the burden of cables.
Underwater wireless communications are usually established using acoustic waves, since electro-magnetic waves propagate only over very short distances. Acoustic communications are governed by three factors: limited, distance-dependent bandwidth; time-varying multipath propagation, and low speed of sound. Together, these constraints result in a communication channel of poor quality and high latency, thus combining the worst aspects of terrestrial mobile and satellite radio channels into a communication medium of extreme difficulty. Moreover, because the acoustic path loss increases with frequency, signals are confined to the low end of the spectrum, where their bandwidth is not negligible with respect to the center frequency. To achieve high information throughput on such channels, phase and amplitude modulation/detection techniques must be considered because of their bandwidth efficiency. Signal processing methods for bandwidth-efficient underwater communications are based on adaptive channel tracking, equalization, and multichannel combining. These methods have been a topic of extensive research over the past decade, resulting in the development of first high-speed underwater acoustic modems. Today, research is active on the design of communication algorithms that will enable improved performance and lower processing complexity, as well as protocols that will enable integration of point-to-point links into autonomous underwater networks.
In this presentation, we overview the channel characteristics, and outline the signal processing methods for state-of-the-art underwater acoustic communications. The performance of various techniques is discussed through a series of experimental results, which include transmission over distances ranging from a few kilometers in shallow water to hundreds of kilometers in deep water, at highest bit-rates demonstrated to date. We conclude with an outline of open research problems.
Biography
 Milica Stojanovic graduated from the University of Belgrade, Serbia, in 1988, and received the M.S. and Ph.D. degrees in electrical engineering from Northeastern University, Boston, MA, in 1991 and 1993. After a number of years with the Massachusetts Institute of Technology, where she was a Principal Scientist, she joined the faculty of Electrical and Computer Engineering Department at Northeastern University in 2008. She is also a Guest Investigator at the Woods Hole Oceanographic Institution, and a Visiting Scientist at MIT. Her research interests include digital communications theory, statistical signal processing and wireless networks, and their applications to mobile radio and underwater acoustic communication systems. Milica is an Associate Editor for the IEEE Journal of Oceanic Engineering and the IEEE Transactions on Signal processing.
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