Date of Award

2002

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Department

Electrical Engineering

Advisor

Donald M. Hummels

Second Committee Member

Bruce E. Segee

Third Committee Member

Duane Hanselman

Abstract

This thesis presents the design and software implementation of an underwater acoustic modem receiver. Communication links in underwater environments face several undesired effects. These include multipath signal reflections, intersymbol interference, and channel fading. This receiver design uses a combination of time and spatial diversity inputs combined with an adaptive feedback equalizer to counteract those effects. The design is based on three modules. A front-end module demodulates and Doppler-compensates the incoming data. A channel combiner module receives data from one or more front ends for spatial diversity and combines repeated transmissions for time diversity. The data from each input channel is time aligned and stored in a 'job' structure. The channel combiner also calculates tap sizes and locations for the feedback equalizer. Completed 'job' structures from the channel combiner are then sent to an equalizer module. The modules are implemented in C language code written and compiled for Analog Devices SHARC digital signal processors. The hardware consists of several processors that are interconnected via link ports. This allows each module to run on a separate processor. It also allows for multiple instances of certain modules to be run simultaneously to provide real-time operation.

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