Matched filter is a filter for detection of signals, matched filter is depend on signal that detect it.
for example you want to detect g(t) and your filter with impulse response h(t), if
h(t) = g(t)* then you have matched filter (h(t) = g(T-t)* is better becuase h(t) =
g(t)* is noncausal) by using matched filter u can maximize recieved power from your signals
The common signal in communication is --> s(t) = ∑ I[n]g(t-nT)exp(-jwt)
if u can remove RF part of signal exp(-jwt) u can work with just ∑ I[n]g(t-nT)
this is lowpass part of the signal, and in most time u can work with it insteade of
s(t) and working with it is easier than working with s(t)
for more information I suggest typical book in communications like Carlson or advanced book like Proakis