Hi Kevin,
Thank you for your links!
However, i am able to direct to /usr/local/share/gnuradio but was unable to
find the examples directory. It seems like the examples do not exist? I am
using Ubutun Deskop 20.04 LTS. Regards, Lannan > On Jul 15, 2020, at 11:27 AM, Kevin McQuiggin <[email protected]> wrote: > > Hi Lannan: > > I am in exactly the same place as you are in regard to learning about digital > modulation and packet transmission in gnuradio. I am working towards > development (and understanding) of a digital transmission and reception > system. My goal is simply to learn how this is done in gnuradio. > > I agree with you in that there is a lack of clear explanatory information > online for this. I have found some examples but they use the deprecated > “packet encoder” and “packet decoder” blocks and are not well-explained. > > I did some research and found some references in forums et cetera that point > to an excellent set of examples in newer gnuradio distributions, see (in > general) /(you local install path)/gnuradio/share/examples/packet. There are > a number of example flow graphs and some hierarchical blocks. > > I went through these but no documentation was evident until I did further > searching and found great in-depth explanatory notes of these flow graphs at > https://www.gnuradio.org/doc/doxygen/page_packet_comms.html > <https://www.gnuradio.org/doc/doxygen/page_packet_comms.html>. > > I am currently reading through these notes and am going to experiment with > the hierarchical blocks to begin with. > > The digital communications notes at > https://www.gnuradio.org/doc/doxygen/page_digital.html > <https://www.gnuradio.org/doc/doxygen/page_digital.html> are also quite > helpful, they parallel the discussion in the guided tutorial we have both > worked through. > > I hope this info helps and good luck with your learning! > > Kevin > > > >> On Jul 15, 2020, at 5:50 AM, lannan jiang <[email protected] >> <mailto:[email protected]>> wrote: >> >> >> Thank you very much. I’ll see what I can do based on your suggestions. >> >> Best regards, >> Lannan Jiang >>> On Jul 15, 2020, at 6:38 AM, Jeff Long <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> The signal source is outputting unsigned bytes. The sample rate is 48k and >>> the tone is 1k. Something I missed before that helps explain your plot ... >>> the signal is rounded down to zero for all but the peak values, since >>> abs(x) < 1 can not be represented without scaling. Packed/unpacked refer to >>> bits of a digital signal. The tone is "analog", but you could think of it a >>> "packed" if your audio codec is PCM (raw samples). PCM is a valid codec. >>> It's what you find in a wav file. The problem you will run into is that any >>> lost or corrupted symbols will ruin the audio. So, you would need to add >>> framing/packetizing and error correction. Maybe someone else has a link to >>> an example that shows how this works in GR. The concepts are not specific >>> to GR. >>> >>> On Tue, Jul 14, 2020 at 10:50 PM lannan jiang <[email protected] >>> <mailto:[email protected]>> wrote: >>> Hi Jeff Long, >>> Thank you so much for your reply. >>> >>> I understand the plot of the signal source now. I have the >>> mpsk_stage6.grc running properly from the tutorial, and was able to compare >>> the transmitting and receiving bit streams. I attached the grc file to this >>> email. Additionally, could you please elaborate more on the byte output of >>> the signal source? Are they packed? Unpacked? >>> Moreover, as you stated that i should encode an analog signal to data >>> before transmission, so does that mean I also have to use codecs in order >>> to transmit a tone? >>> My last question would be: if I were to transmit an mp3 file, which is >>> already encoded, will i be able to recover the audio using audio decoders? >>> >>> Thanks again for your help! >>> >>> Lannan Jiang >>> >>> ps: I apologize for my many questions as they may seem very basic. I am >>> an engineering student and I am greatly thankful for your advice. >>> >>> >>> >>> From: Discuss-gnuradio <[email protected] >>> <mailto:[email protected]>> on behalf of Jeff Long <[email protected] >>> <mailto:[email protected]>> >>> Sent: Tuesday, July 14, 2020 9:57 PM >>> To: GNURadio Discussion List <[email protected] >>> <mailto:[email protected]>> >>> Subject: Re: Question regarding transmission of a tone using QPSK >>> >>> A better explanation of why that plot is correct: if you sample a tone >>> twice per cycle, you see [-1,1,-1,1,...]. Four times per cycle, looks like >>> [-1,0,1,0,...]. Even though it looks discontinuous, it will sound like a >>> tone when played through your sound card due to filtering in the audio >>> software and/or hardware. >>> >>> That tutorial goes through the low level portions of the digital chain, >>> including timing recovery. Framing, error correction and (optionally) an >>> audio codec would all be in addition to the blocks shown in the tutorial. >>> >>> On Tue, Jul 14, 2020 at 9:03 PM Jeff Long <[email protected] >>> <mailto:[email protected]>> wrote: >>> Depending on your sample rate and tone frequency, that plot would be >>> correct. >>> >>> The analog signal needs to be encoded somehow as data before transmission. >>> While you could feed an audio file 2 bits at a time into a QPSK modulator, >>> it's pretty unlikely that you will be able to recover the audio. If you're >>> thinking of "transmitting audio", look into audio codecs. If you're >>> thinking of sending a wav file, you're really just sending packets. Either >>> way, you will need a complete chain that includes error correction, clock >>> recovery, etc. >>> >>> On Tue, Jul 14, 2020 at 3:58 PM lannan jiang <[email protected] >>> <mailto:[email protected]>> wrote: >>> Hi all, >>> I have been following the PSK guided tutorial >>> https://wiki.gnuradio.org/index.php/Guided_Tutorial_PSK_Demodulation >>> <https://wiki.gnuradio.org/index.php/Guided_Tutorial_PSK_Demodulation> . I >>> am on the mpsk_stage6.grc, but I want to transmit a simple tone instead of >>> a random source, so I added a signal source which generates a sine wave. >>> However, here are my questions: >>> >>> 1. I select the output of the signal source as bytes, and the time plot >>> of it is attached. As you can see, the plot looks like bursts. But if I add >>> an audio sink after signal source directly, I hear a constant tone. This >>> does not make sense to me, as I thought I should hear discontinuous sound >>> as the plot shows, could someone explain this? >>> >>> 2. With the first question being said, I am using a constellation >>> modulator (QPSK) that takes 2 bits/symbol. >>> How can I feed the output of signal source ( a 16-bit audio file later >>> on) to the constellation modulator properly? >>> >>> Thanks in advance! >>> >>> Regards, >>> Lannan Jiang >>> >> >
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