Thanks a lot Cinaed for the tips, in particular, the symmetry order and CMA equaliser.
I did what you suggested about sps variable. However, it didn't help. Besides as far as I know form GNURadio documentation, samples/symbol is referring to the samples representing a single constellation symbol so increasing this parameter is equivalent to interpolating the signal. It doesn't have to do anything with the modulation scheme. Please correct me if I am wrong. Cheers, Mansour. On 17 May 2017 at 21:43, Cinaed Simson <cinaed.sim...@gmail.com> wrote: > m-psk for m=2, has 2 samples/symbol and log2(m)=1 - or 1 bit per symbol. > > Also, the polyphase clock has an input of 4 samples and output of 1 sps. > It should have input of 2 sps and output of 1 sps. > > Just change the sps everywhere to 2. > > Also, note there are only 2 symbols in the symbol map of the > Constellation object so for sps equal to 2 the symmetry is 2 - or there > will be 2 clusters on a horizontal straight line. > > Except when you use a tap in the Channel Model of 1+1j which will > probably rotate the line by 45 degrees to the horizontal. > > In any case, this is known as bpsk - or your case dbpsk - differential > bpsk. > > I would add the CMA Equalizer between the Polyphase clock and Costa Loop. > > -- Cinaed > > > > On 05/17/2017 08:59 AM, Mojtaba Mansour Abadi wrote: > > Hi Everyone, > > > > The flowgraph I am implementing is simple and straight forward. I am > > modulating a set of data plus preamble. The modulations I am looking at > > are either PSK or QAM. After a block of "Channel Model" in the > > flowgraph, I want to demodulate the signal and obviously, for fair SNR > > values I should receive the same preamble and data values. > > > > Now the problem is that when I use the deprecated "PSK/QAM Mod" and > > "PSK/QAM Demod", everything works fine. However, based on the examples > > in "/digital/demod" and "/digital/packet" shiped with > > gnuradio companion, when I try to use the "FLL Band-Edge" followed by > > "Correlation Estimator", "Polyphase Clock Sync", and "Costas Loop" to > > compensate the channel for PSK modulation, the results I am getting are > > not correct (see the attached picture and file). > > > > It would be your kind if you could answer my questions please: > > > > 1- What is the correct way of demodulating the received signal? > > 2- In the provided examples, no equalizer is used after "Polyphase Clock > > Sync", whereas in a tutorial available at Gnuradio website a "CMA > > Equaliser" is needed there. So which one is the correct one? > > 3- If I move to QAM modulation, the only thing I need to do would be > > replacing "Costas Loop" with a "Constellation Receiver", right? > > > > Cheers. > > > > Regards, > > Mansour. > > > > https://www.linkedin.com/in/mojtaba-mansour-abadi-4311b451 > > > > > > _______________________________________________ > > 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 > -- Regards, Mansour. https://www.linkedin.com/in/mojtaba-mansour-abadi-4311b451
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