Forum: GNU Radio Re: calc_metric in digital_constellation_receiver

Just wanted to add that if you choose  option four,
ie you have at the output of the constellation_receiver
a phase-corrected complex stream then you can use it
directly as the input to the viterbi_combined
block so that you avoid the use of the
trellis.constellation_metrics_cf block.

Achilleas

Date: Sun, 24 Feb 2013 12:28:07 -0700
From: Ben Reynwar <ben@reynwar.net>
To: Manu T S <manu.t.sree@gmail.com>
Cc: GNURadio Discussion List <discuss-gnuradio@gnu.org>
Subject: Re: [Discuss-gnuradio] calc_metric in
        digital_constellation_receiver
Message-ID:
        <CAHXOypq4nJ7jDf_txTkRdTVakG--FZ9aSpBU2nMyuLCq+Zqx3g@mail.gmail.com>
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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.