Questions on rx_ofdm example in GR 3.7.1

GR 3.7.1
gr-digital/examples/ofdm/rx_ofdm.grc

  1. The OFDM Frame Equalizer block that is downstream from the Header
    Stream Virtual Source block has the Length Tag Key field set to
    length_tag_name, yet all other blocks on the diagram with that field are
    set to length_tag_key (which is the ID of a Variable block at the top of
    the diagram). Is that a mistake? If someone will confirm, I can file the
    bug.

  2. When I try to run this flowgraph, modified for my target’s custom
    source block, I get this error:
    FATAL: Missing a required length tag on port 0 at item #0
    thread[thread-per-block[21]: <block ofdm_frame_equalizer_vcvc (22)>]:
    Missing length tag.

Which led me to question (1) above. However, changing that block to
match the others does not correct the runtime error.

I found a couple of instances of the same error listed in (2) above in
the mailing list, but no one replied to them.

TIA,
Tim

On Tue, Sep 10, 2013 at 09:58:16PM +0000, Monahan-Mitchell, Tim wrote:

GR 3.7.1
gr-digital/examples/ofdm/rx_ofdm.grc

  1. The OFDM Frame Equalizer block that is downstream from the Header Stream
    Virtual Source block has the Length Tag Key field set to length_tag_name, yet all
    other blocks on the diagram with that field are set to length_tag_key (which is
    the ID of a Variable block at the top of the diagram). Is that a mistake? If
    someone will confirm, I can file the bug.

Hm. You make me look like a total scrub.

It seems you’re right. However, on my machine, length_tag_name doesn’t
throw an error. I just can’t see why. GRC itself should figure this is a
problem.

  1. When I try to run this flowgraph, modified for my target’s custom source
    block, I get this error:
    FATAL: Missing a required length tag on port 0 at item #0
    thread[thread-per-block[21]: <block ofdm_frame_equalizer_vcvc (22)>]: Missing
    length tag.

That’s good, actually – it means your block is getting input, which
means it’s receiving headers.

To be honest, the {rx,tx}_ofdm.grc files were more of an illustration of
how the OFDM chain works. I know I’ve used them successfully sometime in
the past, but I’ve changed some stuff in between.

Using the ofdm_tx and ofdm_rx hier blocks should, however, work. Can you
try those?

My main issues when transmitting OFDM is getting a clean spectrum. OFDM
doesn’t like distortions at all.

MB

Which led me to question (1) above. However, changing that block to match the
others does not correct the runtime error.

I found a couple of instances of the same error listed in (2) above in the
mailing list, but no one replied to them.


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

Dipl.-Ing. Martin B.
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

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

Nope, the only thing I did was to set it to 1. I didn’t changed the tag
names or anything else.

On Wed, Sep 25, 2013 at 5:06 PM, Monahan-Mitchell, Tim <

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