[Discuss-gnuradio] QPSK demodulation using GRC constellation decoder not working

Hi,

I am trying to transmit and receive a file using Ettus USRP and GNU Radio Companion. The modulation scheme used is QPSK. I followed the "gnu radio tutorial 7:PSK Symbol recovery" . That worked fine and I was able to recover the file at the receiver end. That tutorial uses a out of tree module "my_qpsk_demod" as the QPSK demodulator. I am trying to replace the "my_qpsk_demod" with "constellation decoder" block. I did that as  shown in the attached figure. After I did this modification, I was not able to receive the file properly. 

When I observe the constellation plot after the costas loop, I can clearly see the four constellation. I really appreciate if you could help me to understand what I am doing wrong and get the code working. 

Thank you very much

Damindra

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Damindra Savithri Bandara,

PhD in Information Technology (Candidate)
George Mason University,
Fairfax,
Virginia