Re: Symbols covered by RRC filter in Rect Constellation Modulator

[George Edwards]

Good morning Jeff! Thanks for the code snippet. I am trying to find the number of data symbols covered by the prototype filter and from your code snippet I can calculate it. It's ncoeff/sps. Thank you! George

On Fri, Aug 6, 2021, 2:10 PM Jeff Long <willcode4@gmail.com> wrote:

From generic_mod_demod.py, here is how the taps are generated. The taps are then used by a polyphase filterbank-based arbitrary resampler. I think the answer to your question is 11.

        nfilts = 32
        ntaps_per_filt = 11
        ntaps = nfilts * ntaps_per_filt * int(self._samples_per_symbol)    # make nfilts filters of ntaps each
        self.rrc_taps = filter.firdes.root_raised_cosine(
            nfilts,          # gain
            nfilts,          # sampling rate based on 32 filters in resampler
            1.0,             # symbol rate
            self._excess_bw, # excess bandwidth (roll-off factor)
            ntaps)
        self.rrc_filter = filter.pfb_arb_resampler_ccf(self._samples_per_symbol,
                                                       self.rrc_taps)

On Fri, Aug 6, 2021 at 2:24 PM George Edwards <gedwards.eng@gmail.com> wrote:

Hello GNURadio Community,

The constellation modulator has an RRC filter and we are allowed to set the alpha and the number of samples per symbol parameters. 

An RRC filter is normally designed to cover a number of symbols to the right and left from the center of its impulse response. Anyone know the number of symbols covered in the GNURadio Constellation Modulator?

Thanks very much!

Regards,

George