The channel filter in GMSK

GNU Radio
1

Hi, Gang

I am reading the GMSK2 code again and have met some interesting
questions.

  1. At the receiver side, why would we use such a channel filter? The
    sampling rate is set to the spd value and the cutoff freq. is simply

  2. Could any friend tell me the meaning of these values and what the
    channel filter is used for? I am confused because obviously the actual
    sampling rate is spd*bit rate.

  3. The channel filter is created using:

self.chan_filt = gr.fft_filter_ccc(sw_decim, chan_coeffs)

why do we use a “fft” filter here, instead of the “gr.fir_filter_ccf”
one?

  1. What will happen if we don’t use this channel filter?

Thank you for your time

Dawei