Publication Date

2016-12-23

Availability

Open access

Embargo Period

2016-12-23

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Applied Marine Physics (Marine)

Date of Defense

2016-09-14

First Committee Member

Harry A. DeFerrari

Second Committee Member

Michael G. Brown

Third Committee Member

Arthur J. Mariano

Abstract

The relationship between dynamic ocean acoustic fluctuations and the underwater communication in shallow waters acoustic propagation channels will be investigated, as they present a challenging environment for the transmission of information, causing inter-symbol interference (ISI) and multipath signal spreading and fading. The study and simulations will be based on data from an upwelling monitoring buoy located in the shallow waters of Arraial do Cabo – Brazil. The focus of this thesis is to perform a systematic analysis of the role of the internal waves and upwelling on phase stability of a signal propagating through the channel, in terms of temporal coherence, using the Monterey-Miami parabolic equation (MMPE) model, and compare two approaches to optimize communication systems: prediction and/or measurement of the channel pulse responses. The first one is based on previous predicted pulse responses, given by MMPE and a matched or inverse filter to retrieve the message through multipath recombination. However, as filtering results begin to erode with time, one can estimate the refresh time of the filters necessary to keep up with real time varying sound speed profiles in these shallow waters. The second approach uses a simultaneous background experiment to directly measure and update the channel pulse response while collecting the message, based on “training pulse response measurements”, classic low intensity M-sequences. Finally, the process called Hyperslice Cancellation by Coordinate Zeroing (HCCO) (Chang, 1992) will be performed to eliminate interferences between the M-sequences and the original messages.

Keywords

underwater acoustic communications; signal processing; maximum length sequences; temporal coherence

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