Forum: GNU Radio calc_metric in digital_constellation_receiver

I want to use trellis codes along with generic_mod_demod.

1. Can I replace the constellation_receiver object with a trellis_metric
followed by a viterbi? If so is it required to have an operation 
equivalent
to phase correction in constellation_receiver? How can I do that?

2. There is a function for metric calculation inside
constellation_receiver. Can I use it to implement viterbi?

Thanks in advance

On Sun, Feb 24, 2013 at 6:36 AM, Manu T S <manu.t.sree@gmail.com> wrote:
> I want to use trellis codes along with generic_mod_demod.
>
> 1. Can I replace the constellation_receiver object with a trellis_metric
> followed by a viterbi? If so is it required to have an operation equivalent
> to phase correction in constellation_receiver? How can I do that?

constellation_receiver has four optional outputs.  The fourth is a
phase-corrected complex number.  You could use this as the input to
your metric calculation.

>
> 2. There is a function for metric calculation inside constellation_receiver.
> Can I use it to implement viterbi?

This function is called by trellis.constellation_metrics_cf which
generates metrics that you can feed into the viterbi block.  Metrics
are calculated for every constellation point, so for large
constellations the efficiency will be appalling.