I'm trying to match a signal with a rectangular pulse shape using a rrc filter. Which alpha (0.25, 0.5 or 0.75) is best for doing this and why? My gut says 0.25 but I really don't understand.

Edit: The output signal looks as follows and was passed through a rectangular filter for pulse shaping: The signal gets transmitted over an SDR and picked by an SDR. The phase part is removed and then I want to do matched filtering using an rrc filter. Rectangular pulse signal

  • $\begingroup$ Could you share the signals? Code? $\endgroup$
    – Royi
    Commented Mar 29, 2023 at 11:33
  • $\begingroup$ Can you share your motivation? It doesn't make much sense to use different filters in Tx and Rx. $\endgroup$
    – MBaz
    Commented Mar 29, 2023 at 14:35

1 Answer 1


I think this is a bad idea (you should use a rectangular pulse shape for the matched filter, not RRC). Among other problems, the RRC filter has long duration (infinite in practice). This will cause intersymbol interference (ISI) at the receiver, with a corresponding loss of SNR and BER.

My first idea would be to minimize the RRC side lobes as much as possible; this means maximizing the roll-off factor (setting $\alpha=1$).

In the end, you may have to run some simulations with different $\alpha$ and see which one offers the best compromise between SNR and ISI.

  • 1
    $\begingroup$ Right! And “integrate and dump” receiver would be one way to implement the optimum matched filter in this case $\endgroup$ Commented Apr 29, 2023 at 11:28

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