Hi! So, first step is to verify that if you used a file source instead of the USRP source, things work. If that works, move on to determining possible effects of the physical transmission.
For that, I'd recommend you use your transmitter as you have it, and on the receiver side, start with a waterfall diagram over a bandwidth larger than your transmitter bandwidth. 1MS/s receiver sampling rate should be pretty OK. Do see the hops in the positions you want? Best regards, Marcus On 27.08.2016 05:09, Ajinkya D Kadam wrote: > Hi Marcus, > > I am not using frequency aligning. > > I think your guess about "frequency offset" thing is possible. Since > we are never transmitting on -187Khz but we do observe a signal over > there. > > The received signal that we observe is just what is being transmitted. > We are not applying any demodulation or receiver synthesis.I directly > connect the USRPSource --> File Sink. So my real concern is that why > is the receiver not even looking at the transmitter sequence as is ??? > > The goal of the experiment is not to get data through, in which case > we would have to deal with further issues. > > Our goal is to observe the transmitter hopping sequence correctly at > the receiver. > > ᐧ > > On Fri, Aug 26, 2016 at 3:28 PM, Marcus Müller > <[email protected] <mailto:[email protected]>> wrote: > > Correct me, but this is 400kS/s – that should really not max out > anyone's system, unless the spread blocks are really terribly > inefficient (I don't think they are); please check this, though! > > If I'm not mistaken, gr-spread doesn't tune the hardware or > anything – it just creates a continuous phase stream that changes > frequency, in a cyclic manner. > > My guess is that the receiver is frequency-offset from the > transmitter, and hence, the demodulator "guesses" the wrong > frequencies. Would that be possible? > > Ajinkya, are you frequency-aligning the two USRPs in any way? > > Best regards, > > Marcus > > On 26.08.2016 21:22, Dave NotTelling wrote: >> I have had issues with scheduling transmissions at ~ 10 ms per >> hop and ending up with transmissions happening on the wrong >> frequencies. Usually it's one channel off. If you slow the >> system down does everything work properly? Also, are you pegging >> out any single core in your system? I have seen lots of issues >> with scheduling bursts when the CPU utilization is high or even a >> single core that's maxed out. >> >> On Fri, Aug 26, 2016 at 3:00 PM, Ajinkya D Kadam >> <[email protected] <mailto:[email protected]>> wrote: >> >> Dave, >> >> Thanks for replying. >> >> we are hopping every 80ms. >> ᐧ >> >> On Fri, Aug 26, 2016 at 12:32 PM, Dave NotTelling >> <[email protected] <mailto:[email protected]>> wrote: >> >> Ajinkya, >> >> How fast are you hopping? I've had loads of issues >> with hopping rapidly and not having the correct >> frequencies used. >> >> -Dave >> >> On Tue, Aug 23, 2016 at 7:16 PM, Ajinkya D Kadam >> <[email protected] <mailto:[email protected]>> wrote: >> >> HI All, >> >> I am using gr-spread >> <https://github.com/CIG-SDR/CIG/tree/master/gr-spread> >> module to transmit a signal using FHSS. When I >> receive the FHSS signal, the received signal has a >> completely different hopping sequence as from the >> transmitted one. I am using USRP N210 for >> transmission and reception. I am not sure why this is >> happening. The transmitted sequence is (frequencies >> in Khz) >> >> 187.5 >> -12.5 >> 162.5 >> -62.5 >> 62.5 >> 137.5 >> -112.5 >> -37.5 >> 112.5 >> -162.5 >> -137.5 >> -87.5 >> 12.5 >> 37.5 >> 87.5 >> >> and the received sequence is >> >> 37.5 >> 62.5 >> 112.5 >> -187.5 >> 12.5 >> 187.5 >> -37.5 >> 87.5 >> 162.5 >> -87.5 >> 0 >> 137.5 >> -137.5 >> -112.5 >> -62.5 >> 37.5 >> 62.5 >> >> I have created a movie out of the images which plots >> the IQ, FFT and WaterFall plot for the transmitted >> signal and the received signal using the >> "plot_psd_base.py" file in gr-utils. Please have a >> look at both of them here >> >> <https://drive.google.com/file/d/0B-Ksc0hMVyDVLW11QW1BekJtS0E/view> andhere >> >> <https://drive.google.com/file/d/0B-Ksc0hMVyDVSmU4YzlBVXA5ZFE/view?usp=sharing>. >> >> >> Please see the attached files for the flowgraphs, I >> am using as the transmitter and receiver. >> >> I have stored the received and transmitted signal to >> a file. Since these are large files I have uploaded >> them to google drive here >> >> <https://drive.google.com/a/nyu.edu/file/d/0B-Ksc0hMVyDVRTdaVTV5ZmhCVkE/view>. >> >> >> Could someone please help me understand the behavior >> I am observing ? >> >> Is this some sort of synchronization issue ? What am >> I missing ? >> >> Thanks in advance. >> >> ᐧ >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> <mailto:[email protected]> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> >> >> >> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] <mailto:[email protected]> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> > _______________________________________________ Discuss-gnuradio > mailing list [email protected] > <mailto:[email protected]> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> >
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