Forum: GNU Radio Re: modulation blocks propagate eob tag?

Hi, With gnuradio 3.6.3 I am using the gr_message_burst_source to 
generate
messages (one message per second)  and set the bob and eob correctly. 
After
this block I connect the following blocks to send bpsk modulated 
messages
: packet_to_unpacket_bb, map_bb, chuncks_to_symbol, rrc_filter and the
uhd_usrp_sink. However, I get many "U" characters in the screen, and 
many
errors in the reception. I think that one or many blocks of the previous
ones do not propagate the tags properly. I appreciate any help to solve
this problem/question. Thank you.

Best regards, Pablo Belzarena.

Hi Pablo,

you can use the tag_debug or metadata file sink blocks to see if your
tags are propagating correctly.

MB

On Mon, Feb 25, 2013 at 04:58:52PM +0000, Pablo Belzarena wrote:
> Hi, With gnuradio 3.6.3 I am using the gr_message_burst_source to generate
> messages (one message per second)  and set the bob and eob correctly. After
> this block I connect the following blocks to send bpsk modulated messages
> : packet_to_unpacket_bb, map_bb, chuncks_to_symbol, rrc_filter and the
> uhd_usrp_sink. However, I get many "U" characters in the screen, and many
> errors in the reception. I think that one or many blocks of the previous ones
> do not propagate the tags properly. I appreciate any help to solve this problem
> /question. Thank you.


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Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

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Research Associate

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KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

On 02/25/2013 10:58 AM, Pablo Belzarena wrote:
> Hi, With gnuradio 3.6.3 I am using the gr_message_burst_source to generate
> messages (one message per second)  and set the bob and eob correctly. After
> this block I connect the following blocks to send bpsk modulated messages
> : packet_to_unpacket_bb, map_bb, chuncks_to_symbol, rrc_filter and the
> uhd_usrp_sink. However, I get many "U" characters in the screen, and many
> errors in the reception. I think that one or many blocks of the previous
> ones do not propagate the tags properly. I appreciate any help to solve
> this problem/question. Thank you.
>

When the EOB goes through the modulator chain, there is some
interpolation in the item count, and the tag ends up not on the very
last item in the burst.

In this project, there is a block to correct this issue, this its called
packet gate or eob gate:
https://github.com/jmalsbury/pre-cog/wiki

-josh