Actually, I think i just found them. Thanks! Lannan Jiang
> On Jul 15, 2020, at 12:05 PM, lannan jiang <jln...@live.com> wrote: > > 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 <mcqui...@me.com >> <mailto:mcqui...@me.com>> 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 <jln...@live.com >>> <mailto:jln...@live.com>> 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 <willco...@gmail.com >>>> <mailto:willco...@gmail.com>> 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 <jln...@live.com >>>> <mailto:jln...@live.com>> 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 <discuss-gnuradio-bounces+jln925=live....@gnu.org >>>> <mailto:live....@gnu.org>> on behalf of Jeff Long <willco...@gmail.com >>>> <mailto:willco...@gmail.com>> >>>> Sent: Tuesday, July 14, 2020 9:57 PM >>>> To: GNURadio Discussion List <discuss-gnuradio@gnu.org >>>> <mailto:discuss-gnuradio@gnu.org>> >>>> 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 <willco...@gmail.com >>>> <mailto:willco...@gmail.com>> 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 <jln...@live.com >>>> <mailto:jln...@live.com>> 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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