Matched filtering is a well-known method frequently used in
digital signal processing to detect the presence of a pattern
in a signal. In this paper, we suggest a time variant matched
filter, which, unlike a regular matched filter, maintains a
given alignment between the input signal and the template
carrying the pattern, and can be realized recursively. We
introduce a method to synchronize the two signals for presence
detection, usable in case direct synchronization between the
signal generator and the receiver is not possible or not
practical. We then propose a way of realizing and extending the
same filter by modifying a recursive spectral observer, which
gives rise to orthogonal filter channels and also leads to
another way to synchronize the two signals.
