Also known as: matched filter
A matched filter is the linear filter that maximises SNR against a known signal shape.1 Its impulse response is a time-reversed copy of the pulse it is matched to.
How it works
By correlating the incoming signal with the expected pulse, it concentrates energy at the ideal sampling instant, giving the cleanest possible symbol decision. For RRC-shaped signals, the receiver’s RRC is the matched filter.
Relevance to SDR
Matched filtering is a standard receive step that improves demodulation of weak digital signals such as AIS and APRS.
Sources
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Matched filter — Wikipedia, on the SNR-optimal time-reversed correlation filter. ↩