Many modern underwater applications require wireles and hence spatial flexible communication links, e.g. for data retrieval from remotely operating autonomous underwater vehicles, for exchanging data in ocean monitoring, or for providing information between submerged systems. For distances of technical relevance this task can be accomplished by means of acoustics only. In general, the underwater acoustic channel is a time-variant and inhomogeneous medium. It is furthermore bandlimiting and dispersive in time and frequency domain, which is in contrast to the increasing need for transmitting large amounts of data in short periods of time over distances up to several kilometers. The motivation to overcome these challenges has attracted considerable research during the past decades that enabled high-bit rate untethered underwater acoustic data transmission, and led to the current developments on the field of underwater sensor networks.
The talk is aimed to provide an introduction to the subject of wireles underwater acoustic communication. Since the transmission conditions within water do significantly differ from effects that are typically encountered in RF applications, the physical characteristics of an underwater acoustic channel are addressed first. Based on the presented characteristics of the physical layer, the processing steps required on the receiver side to restore the transmitted information from the received signal are derived for the exemplarily considered coherent modulation schemes. As an extension to the resulting receiver structure a pre-filter approach will be presented that allows to incorporate possibly available a priori environmental knowledge in order to improve the receivers performance. Finally, results obtained with experimental communication data gathered during the ROBLINKS sea trials conducted in the North Sea will conclude the presentation.
Florian Schulz received the Dipl.-Ing. degree and the Dr.-Ing. degree, both in electrical engineering from the Ruhr-Universität Bochum, Bochum, Germany, in 2001 and 2006, respectively. From 2001 to 2005, he was a Member of a Research Staff in the Signal Theory Group, Department of Electrical Engineering and Information Sciences, Ruhr-Universität Bochum. In 2002, he joined the NATO SACLANT Undersea Research Centre, La Spezia, Italy, as a Summer Research Assistant. From 2005 to 2009, he was a Research Associate at the FGAN Institute for High Frequency Physics and Radar Techniques, Wachtberg-Werthhoven, Germany. Since 2009, he has been with the Submarine Systems Division, Atlas Elektronik GmbH, Bremen, Germany. Dr. Schulz is IEEE Member and joining the IEEE Signal Processing Society and IEEE Oceanic Engineering Society. His research interests are in the areas of statistical signal processing and array signal processing with applications in underwater acoustics, radar, and communication.