Rich, If you could send me that paper, I would really appreciate it. So I'm looking at the test_corr_est.grc file and the only place I see the rrc_taps being used is within the polyphase clock sync, which is on the RX side. Should there be a rrc filter on the TX side as well?
Logan Washbourne Electrical Engineering Graduate Student (Electromagnetics) On Sat, Oct 3, 2015 at 5:28 AM, Richard Bell <richard.be...@gmail.com> wrote: > The taps you use should be the upsampled by nfilt version of your shaping > filter at the tx, scaled appropriately to produce the desired output > amplitude. If you're new to this, then you might need to find a good > resource for polyphase filters and how they are used for timing recovery. I > can reference a paper for you later on if needed. But, from grc if you used > an rrc filter on the tx, it's a matter of making a call to the rrc filter > in the taps parameter of the block. I think there is an example of this in > the gr-digital/examples folder. I'm not in front of a computer so I can't > check for you now. > > Rich > > Sent from my iPad > > On Oct 2, 2015, at 3:06 PM, lwas...@ostatemail.okstate.edu wrote: > > Sent from my Cyanogen phone > On Oct 2, 2015 3:12 AM, Richard Bell <richard.be...@gmail.com> wrote: > > > > I can't open and look at your flow now, but it seems you have the > necessary blocks in there. Here are some things that come to mind: > > > > 1) put a multiply const block in front of the usrp source at the tx. You > don't want to feed values ranging from 1 to -1 but rather ~0.7 to -0.7. > > > > I will try that today. > > 2) keep usrp tx/rx analog gains below 20dB to avoid odd behavior. Keep > the usrps close to each other for this debug. I use 15dB for initial > testing. > > > > I've kept it around 10dB normally, but I will double check. > > 3) Costas loop will only fix small frequency offsets. Try adding an FLL > block before timing sync. > > > > Will do. I don't think it's even getting to the costas loop to be honest, > it seems to not be tripping the correlation estimator block. > > 4) are you sure you used the right taps for the pfb clock sync block? > How did you confirm this? > > > I'm not sure if I used the right taps. I'm just using the ones that were > included in the test_corr_est GRC file. Do you have a method of > confirmation that you would recommend? > > 5) BPSK requires an equalizer if you have a bad channel. Are you using > antennas or a coax cable? > > > > I am using antennas. I'll look into the equalizer. > > Thank you for taking the time to help so far. > > > Rich > > > > Sent from my iPhone > > > > On Oct 1, 2015, at 6:20 PM, Washbourne, Logan < > lwas...@ostatemail.okstate.edu> wrote: > > > >> Rich, > >> > >> The test_corr_est block has the flow graph as follows: vector source-> > constellation modulator -> stream mux(with null source) -> throttle -> > channel model -> correlation estimator -> polyphase clock sync -> costas > loop -> constellation and time gui sinks. > >> > >> For my modified TX grc file I used the following flowgraph: vector > source -> constellation modulator -> stream mux(with null source) -> > constellation and time gui sinks as well as the UHD: USRP sink > >> > >> For the RX grc: UHD: USRP Source -> correlation estimator -> polyphase > clock sync -> costas loop-> constellation and time gui sinks. > >> > >> The grc files can be found at: > https://github.com/loganwashbourne/Logan.git > >> > >> The files are called test_corr_est_TX and test_corr_est_RX. > >> > >> Thanks for your time, > >> > >> > >> Logan Washbourne > >> Electrical Engineering Graduate Student > >> (Electromagnetics) > >> > >> > >> On Thu, Oct 1, 2015 at 3:44 AM, Richard Bell <richard.be...@gmail.com> > wrote: > >>> > >>> Hi Logan, > >>> > >>> Can you give more detail on your synchronization choices for BPSK so > we can tell you what more you may need to do? > >>> > >>> Rich > >>> > >>> Sent from my iPhone > >>> > >>> > On Sep 30, 2015, at 7:14 PM, Washbourne, Logan < > lwas...@ostatemail.okstate.edu> wrote: > >>> > > >>> > Hello, > >>> > > >>> > This is somewhat of an update to a previous post I made from last > week. After talking to Julian and Martin, it was made clear to me that I > needed to use a correlation system to insure my receiver would be synced up > to my transmitter when trying to communicate over the air. > >>> > > >>> > I am trying to utilize the Correlation Estimator block to help me > achieve those means. In order to ease myself into it, I am trying to turn > the test_corr_est.grc example into an over the air program. I am getting > communication between the transmitter and receiver(essentially I just split > the grc program in two and took out the throttle block and the channel > model and replaced them with UHD blocks). Now, I don't get any O's or L's > or an abundance of U's, and I can clearly see data coming in on the RX > side, but it seems to be a lot of noise, but noise generated by the TX > side, because it goes away when I stop transmitting. The center frequency > is 2.48GHz and the sample rate is 250k samples/sec. > >>> > > >>> > My testing method is plotting the constellation symbols right before > they get sent out on the TX side and then plotting them right after the UHD > block on the RX side. It is only bpsk and the symbols are covering all four > quadrants. > >>> > > >>> > I haven't changed any settings on the polyphase clock sync or the > modulation scheme. > >>> > > >>> > This is a little rambly but I appreciate your time, > >>> > > >>> > Logan Washbourne > >>> > Electrical Engineering Graduate Student > >>> > (Electromagnetics) > >>> > > >>> > _______________________________________________ > >>> > Discuss-gnuradio mailing list > >>> > Discuss-gnuradio@gnu.org > >>> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >> > >> > >> _______________________________________________ > >> Discuss-gnuradio mailing list > >> Discuss-gnuradio@gnu.org > >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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