The matched-lag filter: Detecting broadband multipath signals with auto- and cross-correlation functions

Signal detection is considered for uncertain noise variance and a broadband source of unknown waveform and emission time. The signal travels to the re ceivers along paths with unknown delays. Using a new "matched-lag filter," the presence or absence of the signal is estimated from the auto- and cross -correlation functions of the receptions. Like a matched filter, correlatio n functions provide the first stage of gain in signal-to-noise ratio becaus e the paths are assumed to be partially coherent. The second stage achieves additional gain by searching only over physically possible arrangements of signals in the auto- and cross-correlation functions while excluding forbi dden arrangements. These stages enable the marched-lag filter to behave lik e a matched filter within a matched filter. In an ideal case, simulations o f the matched-lag filter yield probabilities of detection that are, with on e and two receivers, 4.1 and 366 times, respectively, that obtained from th e conventional energy detector at a false-alarm probability of 0.001. The m atched-lag filter has applications to wireless communications and the detec tion of acoustic signals from animals, vehicles, ships, and nuclear blasts. The matched-lag filter more completely describes signal structure than sto chastic detection and communication theories whose specified auto-correlati on function does not prohibit forbidden arrangements. (C) 2001 Acoustical S ociety of America.