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
PSK_Mod_Demod.grc
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