Thanks for the reply, Michael. As you said, I found a lot of discussions about this topic, but no answers as to the solution of the issue.
Some things that I tried to change were the fft length (changed to 128 from default 64), CRC length (32 to 64) and I changed the constant multiplier block such that the abs() of the Tx waveform was < 1.0 approximately. All with no luck, sadly. On Thu, Jul 5, 2018 at 8:06 PM, Michael Dickens <michael.dick...@ettus.com> wrote: > Hi Usama - I'm confident that if you searched back through the GR > discussion archives, you'd find discussions about this topic: < > https://lists.gnu.org/archive/cgi-bin/namazu.cgi? > query=header_payload_demux0&submit=Search%21&idxname= > discuss-gnuradio&max=20&result=normal&sort=score >. > > The "Parser returned #f" means that the OFDM header didn't pass CRC, which > generally means that the "SNR" isn't adequate, but it could mean other > things too. There are numerous possible issues that you will encounter when > using GR's OFDM. > > * Start with the -default- OFDM settings (e.g., FFT of 128, C/P of 32) and > see if those work. > > * Add a "gain" block immediately after the Tx OFDM block, with settings > from (say) -10 dB to +10 dB; play around & see what happens on Rx. You'll > want the Tx OFDM block abs() output to average around sqrt(1/2) or so, but > less than 1.0; peaks will typically be over 1.0. Get the gain from above > such that this is the case & you're one step closer. This value decreases > the chances of saturating the USRP on Tx. > > * After you've gotten a stable system working (gain is the key when using > default OFDM parameters), start playing with other OFDM parameters: > constellation, FFT length, and so forth --> BUT: one at a time. > > * If you find one that doesn't work, reset its values and go to another > one. If some parameter continues to be stubborn, post back here with your > progress, tests & actual GRC script asking for help again. > > Hope this is useful! - MLD > > On Thu, Jul 5, 2018, at 4:57 AM, Usama Saeed wrote: > > Hello, this is my first time posting a question: > I tried using the ofdm_tx and ofdm_rx examples with two USRP B200s, but > even though I could see the ofdm spectrum on the receiver end, the time > graph at the end of the demodulation was blank (straight line at 0) and I > received the error > > "gr::log :INFO: header_payload_demux0 - Parser returned #f > gr::log :INFO: packet_headerparser_b0 - Detected an invalid packet at item > 6720" > > The associated screenshots are posted on this page: > > https://dsp.stackexchange.com/questions/50283/why-does-my- > ofdm-demod-in-gnu-radio-not-return-anything > > Thank you for any assistance. > > *_______________________________________________* > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > >
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