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Performing the required compensation steps for PSK/QAM modulations at the receiver

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Performing the required compensation steps for PSK/QAM modulations at the receiver

Mojtaba Mansour Abadi
Hi Everyone,

The flowgraph I am implementing is simple and straight forward. I am modulation a set of data and a known preamble. The modulations I am looking at are either PSK or QAM. After a block of "Channel Model", I want to demodulate the signal and obviously, for fair SNR values I should receive the same preamble and data values.

Now the problem is that when I use the deprecated "PSK/QAM Mod" and "PSK/QAM Demod", everything works fine. However, based on the examples in "/digital/demod" and "/digital/packet", when I try to use the "FLL Band-Edge" followed by "Correlation Estimator", "Polyphase Clock Sync", and "Costas Loop" to compensate the channel for PSK modulation, the results I am getting are not correct.

It would be your kind if you could answer my questions please:

1- What is the correct way of demodulating the received signal?
2- In the provided examples, no equalizer is used after "Polyphase Clock Sync", whereas in a tutorial available at Gnuradio website a "CMA Equaliser" is needed there. So which one is the correct one?
3- If I move to QAM modulation, the only thingĀ I need to do would be replacing "Costas Loop" with a "Constellation Receiver", right?

Cheers.

PS: the flowgraph I am using is attached to this email.

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