Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
Ah thanks! Makes perfect sense! For my transmit/receive issue, I found out there is always a random phase offset upon tuning of the LOs. So I set up a matlab script that will correlate the two IQ streams and find this offset. While it is still running, I implement this offset in GNU and I do indeed see the BER drop. The issue is, it doesn't drop very deep. Certainly not like the example simulation. I need to investigate the waveforms to see if there is too much noise. I will look at this over the next few days and if I have any more questions I will report back here. I don't want to overstay my welcome in regards to asking too many questions. Thanks again! From: Achilleas Anastasopoulos [anas...@umich.edu] Sent: Tuesday, November 20, 2018 3:08 PM To: Matthew J. Brandsema Cc: Discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise Hi Mathew, the random source outputs bytes with numbers 0 or 1 (NOT 2). This single bit information is "packed" into a byte that is the input to the QAM modulator. The QAM modulator internally breaks up these bytes and uses every 4 bits to signal the 16QAM constellation. best, Achilleas On Tue, Nov 20, 2018 at 3:03 PM Matthew J. Brandsema mailto:mjb...@arl.psu.edu>> wrote: Hello, When I switched AC coupling off, it just went blank. So instead, I saved the waveforms to a file and plotted the result in Matlab. See attached for plots. The blue curve are the data before modulating, and the red x's are the data after demodulating. They are lined up! Thanks so much for the help in getting this working!!! I noticed the random numbers are only 0, 1 and 2. How the heck does this work for 16 QAM? How does it encode 3 numbers to 16 symbols? My next step is to transmit and receive using two Ettus radios next. I got them to transmit and receive but I can't seem to find a delay that will make them sync up like I did with the file you sent. I saved their IQ waveforms to see how out of sync they are by doing a correlation and the correlation peak seem to be changing between data collects. Does anyone have any idea of what might be happening? (Sorry to add another question, I have been trying all day to get this working). From: Achilleas Anastasopoulos [anas...@umich.edu<mailto:anas...@umich.edu>] Sent: Tuesday, November 20, 2018 1:25 PM To: Matthew J. Brandsema; Discuss-gnuradio@gnu.org<mailto:Discuss-gnuradio@gnu.org> Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise Can you switch off the AC-coupling, and check the scope plot again. Also, maybe useful to have markers instead of just lines. The two streams should be perfectly synchronized (for low noise) and as noise gets higher some of the demodulated bits are in error. This is perfectly OK. Achilleas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
Hello, When I switched AC coupling off, it just went blank. So instead, I saved the waveforms to a file and plotted the result in Matlab. See attached for plots. The blue curve are the data before modulating, and the red x's are the data after demodulating. They are lined up! Thanks so much for the help in getting this working!!! I noticed the random numbers are only 0, 1 and 2. How the heck does this work for 16 QAM? How does it encode 3 numbers to 16 symbols? My next step is to transmit and receive using two Ettus radios next. I got them to transmit and receive but I can't seem to find a delay that will make them sync up like I did with the file you sent. I saved their IQ waveforms to see how out of sync they are by doing a correlation and the correlation peak seem to be changing between data collects. Does anyone have any idea of what might be happening? (Sorry to add another question, I have been trying all day to get this working). From: Achilleas Anastasopoulos [anas...@umich.edu] Sent: Tuesday, November 20, 2018 1:25 PM To: Matthew J. Brandsema; Discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise Can you switch off the AC-coupling, and check the scope plot again. Also, maybe useful to have markers instead of just lines. The two streams should be perfectly synchronized (for low noise) and as noise gets higher some of the demodulated bits are in error. This is perfectly OK. Achilleas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
I just got it to go to -18 dB at a delay of 24. I apologize, my previous email was premature. Let me play around a bit more before emailing. From: Matthew J. Brandsema Sent: Tuesday, November 20, 2018 7:36 AM To: anas...@umich.edu; Discuss-gnuradio@gnu.org Subject: RE: [Discuss-gnuradio] Packet Decoder Breaking when adding noise Hello, I don't have QT gui so I had to convert to WX blocks (how do I install QT?). I cannot get the BER to change appreciably, no matter what delay I set. The best I can get it to is only about -1 dB. I will keep playing with it. From: Achilleas Anastasopoulos [anas...@umich.edu] Sent: Monday, November 19, 2018 5:37 PM To: Matthew J. Brandsema; Discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise I attach a simple grc file that works for me. Using the delay10/delay sliders try to align the input/output bit stream. (in this example this happens at delay=12, but it may be different for you...) Then play with the noise variance; you will see the BER changing slowly as you go around values = -6,-5,-4 let me know if this works for you, Achilleas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
Hello, I don't have QT gui so I had to convert to WX blocks (how do I install QT?). I cannot get the BER to change appreciably, no matter what delay I set. The best I can get it to is only about -1 dB. I will keep playing with it. From: Achilleas Anastasopoulos [anas...@umich.edu] Sent: Monday, November 19, 2018 5:37 PM To: Matthew J. Brandsema; Discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise I attach a simple grc file that works for me. Using the delay10/delay sliders try to align the input/output bit stream. (in this example this happens at delay=12, but it may be different for you...) Then play with the noise variance; you will see the BER changing slowly as you go around values = -6,-5,-4 let me know if this works for you, Achilleas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Packet Decoder Breaking when adding noise
Hello, Thanks for your replies! When I do that, the demodulator outputs unpacked bytes (0s and 1s). I tried using the “Pack K Bits” and “Unpacked to Packed” blocks separately (setting K = 8) and it did not work. By “did not work” I mean, my input into the modulator were numbers between 0 and 15, and when I pack 8 bits at a time, I get numbers between 0 and 255. --- Matt Brandsema Assistant Research Professor Applied Research Laboratory at Penn State University Phone: c: (201) 259-3584 w: (814) 865-5783 From: Achilleas Anastasopoulos [mailto:anas...@umich.edu] Sent: Monday, November 19, 2018 10:15 AM To: Matthew J. Brandsema ; Discuss-gnuradio@gnu.org Subject: [Discuss-gnuradio] Packet Decoder Breaking when adding noise ...neither do you want the extended FEC encoder/decoder. Just send random symbols through the QAM modulator, add noise and demodulate with the QAM demodulator. Achilleas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
