Hi,

I am trying to transmit messages from a message source modulated using
QPSK. A message is transmitted in every second. At the receiving end I am
writing the messages to a message sink. I am using Etuss USRP N200 to test
the setup.

The problem is I do not receive the message at the other end. When I
observe the constellations at the receiver  it shows that the QPSK
demodulator does not remain synchronized.

When I tried this in a simulation environment (using a channel model) the
experiment works fine. If I transmit a file using this setup it works fine
too. But when I transmit a message every 1 second it is not transmitting.

The transmitter end: msg source -->packet encoder --> QPSK modulator -->
USRP sink

Receiver end: USRP source --> Poly phase clock sync --> CMA equilizer -->
Costas loop --> QPSK demodulator  --> Packet decoder --> msg sink

I really appreciate if you could help me to solve this issue.

Thank you
Damindra
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