Waveform design and diversity for shallow water environments

In this chapter, we employ a general signal characterization based on the normal-mode model for shallow water environments that is applicable to a large class of signals. This characterization is based on a frequency domain formulation that can be used with narrowband as well as wideband signals. The normal-mode characterization assumes perfect waveguide conditions, and as a result, it consists of a homogeneous fluid layer with a soft top and rigid bottom. This environment characterization describes a linear time-varying (LTV) dispersive system which can cause different frequencies to be shifted in time by different amounts. Such dispersive signal transformations are specific to the nature of the environment that the signal propagates through, and they can severely limit the performance of underwater acoustic applications such as communications and sonar. In order to improve the performance of these underwater applications, we propose methodologies that exploit dispersion by waveform design and diversity.