Physics‐based performance prediction model for a coherent communications algorithm.

Abstract

A demodulation algorithm for coherent underwater acoustic communications may start by applying a finite impulse response (FIR) filter matched to the response of the channel. Relevant design parameters are the length of the FIR filter and the rate at which it must be updated. The performance of the algorithm as a function of these design parameters can then be quantified in terms of the mean‐squared error (MSE) in the soft demodulation output. In terms of propagation physics, the length of the FIR filter is related to the number of acoustic paths retained as usable signal, and the required update rate is related to the time variation of the channel. In the present study, scattering by the sea surface is the assumed source of time variation. A model is developed for the MSE as a function of the design parameters. The Kirchhoff approximation is used to model acoustic paths that may have undergone multiple reflections by the sea surface. Required model inputs include the grazing angle, the significant wave height, and the dominant period for the surface waves. Model predictions are compared to published experimental results. [Work supported by ONR.]