A Simple Yet Effective Metric for Assessing Doppler Tolerance

The Doppler tolerance of a waveform refers to its behavior when subjected to fast-time Doppler shift imposed by scattering that involves nonnegligible radial velocity. The delay/Doppler ambiguity function characterizes this behavior, with notable attributes of Doppler-dependent mismatch loss (relative to zero Doppler) and possible offset in delay estimation. Previous effort has gone into establishing decision-based criteria where a binary judgement of being Doppler tolerant or not is made. Here, we consider the utility of a simple, yet effective measure of the degree of Doppler tolerance arising from a fundamental attribute of the ambiguity function that is also convenient to extract. This metric is examined in the context of a variety of different waveform classes including traditional linear/nonlinear chirps, noise-like signals, and phase codes. Extension to wideband operation is likewise considered. The purpose in doing so is to establish a consistent standard that can be readily applied, thereby permitting easy assessment across different parameterizations, as well as introducing a Doppler “quasi-tolerant” trade-space that can ultimately inform automated/cognitive waveform design in increasingly complex and dynamic radio frequency (RF) environments.