[Discuss-gnuradio] [QPSK modulation and demodulation using PSK mod and demod blocks]

[Minh Pham]

Dear all,

My name is Minh T. Pham, and I'm completely new to GNURadio. I want to learn
more about QPSK modulation and demodulation using GNURadio, so I started
reading through and follow the "GNURadio Guided Tutorials". In Tutorial 7:
PSK Symbol recovery, the model utilizes Constellation modulator for QPSK
modulation, and a QPSK demod block built in previous tutorials. In my
experiment, however, I want to use the blocks "PSK mod" and "PSK demod"
instead. (the block diagram is shown below)

<http://gnuradio.4.n7.nabble.com/file/n62774/QPSK_mod_and_demod.qpsk_mod_and_demod>
 

Unfortunately, when I look at the result, it seems that the system fails to
recover the information I sent:

<http://gnuradio.4.n7.nabble.com/file/n62774/Result.result> 

The constellation plot shown that the timing recovery works just fine, but
the bits I received in the end are just incorrect.
There are several possibilities for this issue:
 1. I had the wrong configuration for the PSK demod block
 2. The way I decode the information is incorrect
 3. The timing recovery process produced a false result
Please help me find the issue and a way to resolve it.

Sincerely,
Minh.



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