Multisource time delay estimation subject to receiver frequency errors

An electronic warfare (EW) system with two spatially separated intercept receivers, targeting military communication systems is considered. The EW system estimates the direction-of-arrival via a correlation-based time-difference-of-arrival (TDOA) method without any prior knowledge of the signals-of-interest. An important practical consideration is the oscillator frequencies of the two intercept receivers where a difference, or error, degrades the TDOA estimator performance. A measure of this degradation, or loss in power due to the frequency error, is derived and used to describe the robustness against receiver frequency errors. In the multisource scenario, time and frequency overlapping sources can be separated using direction-filtering of the cross-correlation function between the receiver outputs with good result if one signal at a time can be selected by the direction-filter. However, the performance of the considered estimator is degraded in a multisource scenario compared to the single source case.