[Discuss-gnuradio] Bug in mspk_receiver_cc?

[Stefan Brüns]

there seems to be a bug in the costas loop. As far as I understand, in case of 
nonzero carrier offset, each incoming sample should be rotated with a linear 
increasing phasor (assuming a constant offset). This is done with the 
following code:

void
gr_mpsk_receiver_cc::mm_sampler(symbol) {
  d_phase += d_freq;
  nco = gr_expj(d_phase+d_theta);
  sample = nco*symbol;
}

This looks fine so far for me (although I dont understand why theta is added 
every time, and not once in the initialization of d_phase ...), but there is 
also the following:

void
gr_mpsk_receiver_cc::phase_error_tracking(sample) {
...
  d_phase += d_freq + d_alpha*phase_error;
...
}

So d_phase gets incremented by d_freq on every incoming sample, and once every 
symbol.

Any comments, is this actually a bug?

Stefan

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