Hi Cinaed, Thanks a lot for the complete reply. I appreciate it.
I will implement your suggestions and see what the output will be and let you know. Cheers. On 25 May 2017 at 09:56, Cinaed Simson <cinaed.sim...@gmail.com> wrote: > Suppose someone asked you to implement your flow graph on a transmitter > and receiver separated by an air gap. > > Where would you tap into the signal with the Correlation Estimator? > > I would tap into the signal at the end of the receiver - at the virtual > source with the decoded signal - or the very end of the flow chart. > > And you've already demonstrated the output of the flow graph is the same > as input, i.e., you can reliably transit and receive a BPSK signal. > > Instead of trying to cram all these block into 1 flow graph, there's an > easier way. > > Replace the entire flow graph with a Channel Model. Use a complex vector > equal to the sum of the data and preamble. Feed the complex vector into > a complex Stream to Tagged Stream block and then feed the tagged stream > into the Channel Model. Place the Correlation Estimator on the other > side of the Channel Model and you have something that begins to look like > > <gnuradio_root>/share/gnuradio/examples/digital/pack > /example_corr_est.grc > > Use your Constellation Object to configure the Modulate Vector for BPSK. > > And after you've work out all the details of the Correlation Estimator, > you can graph it back onto the original flow graph. > > -- Cinaed > > > On 05/24/2017 10:32 AM, Mojtaba Mansour Abadi wrote: > > Hi Everyone, > > > > > > I am trying to benefit "Correlation Estimator" block to tag the preamble > > of the transmit bit sequence in a QPSK-based system > > > > > > The modulation is done as: > > Data + Preamble -> Constellation Modulator > > > > > > The way I am doing the demodulation is: > > AGC -> FLL Band-Edge -> Correlation Estimator -> Correlation Estimator > > -> Polyphase Clock Sync -> CMA Equaliser -> Costas Loop > > > > The hard decoding is done as: > > Constellation Decoder -> Differential Decoder -> Map -> Unpacked to > Packed > > > > After I execute the flowgraph, for a few seconds everything works fine > > and I receive the correct sequences. However, after a while, the > > received bits are not correct and their pattern changes periodically. > > > > When I bypass the "Correlation Estimator" block, everything works fine > > and I receive the correct data. > > > > I am confused. Is the correlation block suppose to deteriorate the > > demodulation performance? > > > > The flowgraph is attached to the email. > > > > > > -- > > 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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