Frequency selective TDOA/FDOA cross-correlation

DETAILED DESCRIPTION An object of this invention is the provision of a robust, reliable digital signal processing system for identifying a signal of interest in an environment of dense interfering signals which only partially overlap the signal of interest.
Another object of this invention is the provision of a signal processing system for identifying a signal of interest which requires a priori knowledge only of the approximate frequency and bandwidth of the signal of interest and does not require detailed knowledge of the signal of interest or detailed knowledge of the interfering signals.
The third object of this invention is the provision of a signal processing system for providing a means of obtaining accurate TDOA and FDOA measurements of a signal of interest in a dense interfering signal environment.
Briefly, this invention contemplates the provision of a digital signal processing system in which a time series of cross-spectra (called a waterfall in the art) are computed from transforms applied to overlapping data sets comprising the two received digital data streams, which include the signal from the emitter of interest and one or more partially overlapping interfering signals.
For each cross-spectra frequency, a transform is calculated in the time direction to create a frequency difference of arrival dimension.
Regions within the transformed cross-spectrum that are associated with individual emitters are then identified based on the fact that a given emitter's transformed cross-spectrum phase changes linearly with frequency near the peak FDOA for the emitter.
A random phase change identifies regions where noise or interference is corrupting the phase measurements, and jumps in linear phase identify transitions between emitters.
The frequency region(s) associated with the emitter of interest are selected based on the approximate frequency and bandwidth information provided.
Applying an inverse transform for the frequencies, identified as associated with the emitter of interest, creates a time difference of arrival dimension corresponding to each frequency difference of arrival value