Underwater communication via particle velocity channels : principles, channel models, and system design

A vector sensor is capable of measuring important non-scalar components of the acoustic field such as the particle velocity, which cannot be obtained by a single scalar pressure sensor. In the past few decades, extensive research has been conducted on the theory and design of vector sensors. On the other hand, underwater acoustic communication systems have been relying on scalar sensors only, which measure the pressure of the acoustic field. By taking advantage of the vector components of the acoustic field, such as the particle velocity, the vector sensor can be used for detecting the transmitted data. In this dissertation, the concept of data detection and equalization in underwater particle velocity channels using acoustic vector sensors was developed. System equations for such a receiver were derived and channel equalization using these sensors was formulated. A multiuser system using vector sensors and space time block codes was also developed, which does not use spreading codes and bandwidth expansion. This is particularly important in bandlimited underwater channels. With regard to channel models for particle velocity channels, characterization of particle velocity channels and their impact on vector sensor communication systems performance were therefore of interest. In multipath channels such as shallow waters, a vector sensor receives the signal through several paths and each path has a different delay (travel time). Motion of the transmitter or receiver in a multipath channel introduces different Doppler shifts as well. Those introduce different levels of correlation in an array of vector sensors. Therefore, in this dissertation, a statistical framework for mathematical characterization of different types of correlations in acoustic vector sensor arrays was developed. Exact and closed-form approximation correlation expressions were derived which related signal correlations to some key channel parameters such as mean angle of arrivals and angle spreads. Using these expressions, the correlations between the pressure and velocity channels of the sensors could be calculated, in terms of element spacing, frequency and time separation. The derived closed-form parametric expressions for the signal correlations can serve as useful tools to estimate some important physical parameters as well. Knowledge of the delay and Doppler spreads in acoustic particle velocity channel is also important for efficient design of underwater vector sensor communication system. In this dissertation, these channel spreads were characterized using the zero crossing rates of channel responses in frequency and time domain. Useful expressions for delay and Doppler spreads were derived in terms of the key channel parameters, mean angle of arrivals and angle spreads. These results are needed for design and performance predication of communication systems in time-varying and frequency-selective underwater particle velocity channels

Abstracts of manuscripts submitted in 1993 for publication

This volume contains the abstracts of manuscripts submitted for publication during calendar year 1993 by the staff and students of the Woods Hole Oceanographic Institution. We identify the journal of those manuscripts which are in press or have been published. The volume is intended to be informative, but not a bibliography. The abstracts are listed by title in the Table of Contents and ar grouped into one of our five departents, Marine Policy Center, Coastal Research Center, or the student category. An author index is presented in the back to facilitate locating specific papers

Investigating the build-up of precedence effect using reflection masking

The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels

Conference Proceedings of the 3rd Biennial Symposium on Turbulence in Liquids

The Third Biennial Symposium on Turbulence in Liquids showed further progress in the investigator\u27s ability to measure turbulence parameters and in the general understanding of turbulence. The most impressive advances in measurement seemed to be the ability to measure deeper into the turbulent boundary layer in order to obtain profiles over the entire turbulence production region and the rapid development of conditioned-sampling techniques for studying hypotheses for mechanisms