| Because electromagnetic waves are strongly attenuated in the ocean, researchers have turned to the use of acoustics for such problems as communications and detection. Acoustic propagation in the ocean is dominated by interactions with the surface and seafloor, leading to complicated arrivals structures. The computing power needed to model this environment makes the use of adaptive processes such as time-reversal an attractive alternative. Further, the use of self-adaptive processes, which use the data itself to influence the processing, have proven to be both robust and powerful. This thesis concerns itself with four such processes. The first derives the canonical minimum mean-squared error linear equalizer (MMSE-LE) as a self-adaptive process related to iterative time reversal. The next chapter analyzes the feasibility of using a horizontally-aligned synthetic aperture to perform time reversal communications. Also derived in this thesis are bounds on the capacity of a strongly dispersive channel, such as those found in the ocean, with practical constellation-based constraints on the transmitted signal. A final self-adaptive process is described in an attempt to classify a target as resonant or non-resonant based on the measured back-scattered field. |
