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

[Martin Braun]

Looks like you're not resolving the pi/2 ambiguity. To do that, you
either need something more sophisticated, or differential modulation.

-- M

On 02/07/2017 11:42 AM, Minh Pham wrote:
> 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.
> 
> 
> 
> --
> View this message in context: 
> http://gnuradio.4.n7.nabble.com/QPSK-modulation-and-demodulation-using-PSK-mod-and-demod-blocks-tp62774.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
> 
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