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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Fwd: Questions on rx_ofdm example in GR 3.7.1 |
Date: | Tue, 17 May 2016 12:41:58 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
Hi Han, You replied to a thread from September 2013 – which is totally OK, but many of us don't have the original mail in their archives, so here it is: Hi Tim.a bit of research led to this original question: 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.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.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. MBWhich 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. So, please note: gr-digital has seen quite some patches since 2013; I wouldn't assume everything said back then still applied today. You mention header_eq=digital.ofdm_equalizer_vcvc(now, did you maybe mean ofdm_frame_equalizer_vcvc So, before we dig deeper into this, would you mind explaining which question exactly you're referring to when you said I think it might be worth giving us a bit of an overview over what you're building, what goes wrong, and how you're trying to fix this.I have faced the same question in my work, Right now, I'm a bit confused, sorry :( Best regards, Marcus On 17.05.2016 09:50, hgajiayou wrote: Hey there: I have faced the same question in my work, according to your solution that set the Fixed Frame Length parameter to 1. I checked the OFDM Frame Equalizer block in ofdm_txrx.py(the file direction: gnuradio->gr-digital->python->digital), and i found the next codes: header_eq=digital.ofdm_equalizer_vcvc( header.equalizer.base(), cp_len, self.frame_length_tag_key, True, 1 #Header is 1 symbol long, ) According to your solution, which parameter i need to set to 1 in the codes? I'm a green hand in Gnuradio, hoping for your answer . Han -- View this message in context: http://gnuradio.4.n7.nabble.com/Fwd-Questions-on-rx-ofdm-example-in-GR-3-7-1-tp43833p60074.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio |
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