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.


Date: Sun, 24 Feb 2013 12:28:07 -0700
From: Ben R. [email protected]
To: Manu T S [email protected]
Cc: GNURadio D.ion List [email protected]
Subject: Re: [Discuss-gnuradio] calc_metric in
[email protected]
Content-Type: text/plain; charset=ISO-8859-1

On Sun, Feb 24, 2013 at 6:36 AM, Manu T S [email protected] 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.

  1. 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.