Changing code rate (FEC)

GNU Radio
1

Hi,

I would like to be able to change the code rate with PSK and QAM
modulations (e.g QPSK 3/4, 16QAM 1/2). I was thinking of using a FEC
encoder/decoder as you can see in the attached files but it doesn’t
really work. I’m trying to send a video file and I would like to be able
to read the received video. What can I do to make it work or is there
another way to change the coding rate?

Thanks

2

On Wed, Aug 26, 2015 at 8:07 PM, Eric E. [email protected] wrote:

Attachments:
http://www.ruby-forum.com/attachment/11055/fec1.jpg
http://www.ruby-forum.com/attachment/11056/fec2.jpg
http://www.ruby-forum.com/attachment/11057/fec3.jpg

Dynamics here haven’t been tested much. A lot of the codes defined now
are
single-purpose because there’s a lot of initialization and setup that
occurs that might interfere with the running of things. It’d be
interesting
to see where different codes can be modified live. But for the CC
encoder/decoder you’re using, look at the man page:

http://gnuradio.org/doc/doxygen/classgr_1_1fec_1_1code_1_1cc__decoder.html

That code is highly optimized to do that one rate and K factor that it
does.

You might have better luck making multiple variables and switching them
in
and out of the FEC extended encoder/decoder blocks. I feel we might have
to
do something to invalidate any data due to changes in cipher/plain text,
though.

Tom

3

Thank you for your reply. So from what I understand, code rates other
than the default one are untested and the code rate is difficult to
change? Also, I still can’t read the video at the output of the decoder.
I used the highly optimized default values (R=2, K=7, poly: 79, 109) and
the output of the decoder is still different that my input signal
(before the encoder) so I’m unable to read my output video. Is there
something that I’m missing? Thanks.