QPSK Demodulation of Modulated .wav file

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muhammad ahmad
muhammad ahmad on 22 Jun 2021
Commented: muhammad ahmad on 24 Jun 2021
I have a QPSK modeulated .wave file that i need to demodulate using simulink . how can i use this file so in simulink to access qpsk MODULATED DATA
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Walter Roberson
Walter Roberson on 22 Jun 2021
What is the difference in file format between a .wav file that contains QPSK modulated data, compared to a .wav file that contains audio data?
In your Simulink diagram, is there a different signal type for QPSK modulated data, compared to unmodulated data?
muhammad ahmad
muhammad ahmad on 23 Jun 2021
The .wav file that contain audiodata has a clear sound output if we play it while a modulaed .wav file has noisy output we cant hear any clear sound of it. linking the specturum plots for both type of files to eloborate the point

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Answers (1)

Walter Roberson
Walter Roberson on 24 Jun 2021
Suppose you were doing a physics experiment, and that for one of the components you had distilled water, and for another component you had melted snow (for example you might be studying how heavy metals from pollution accumulate in snow.)
Question: do you need a different kind of container for the distilled water compared to the melted snow? Or do you use the same kind of container?
Question: do you need a different kind of pipe for the distilled water compared to the melted snow? Or do you use the same kind of pipe?
If one of the two components was liquid hydrogen, then you very definitely would use different kinds of containers and different kinds of pipes, so there are circumstances under which they need to be different. But is melted snow compared to distilled water sufficiently different for that purpose?
Now: you have a wav file that contains data that has been processed to QPSK modulate it. And you have another wav file that contains data that has not been QPSK modulated. Do the two need different kinds of files, and different kinds of Simulink signals? Or can use the same kind of file and the same kind of Simulink signal?
... because if they can use the same kind of file and signal, then your question should not be specifically how to get QPSK into the SDR decoder: your question should just be how you can get audio data from a file into Simulink, and what (if any) steps you need to turn the output of the audio file reader into the kind of signal used by the SDR decoder.
I know that recently someone replied to you with the Simulink block needed to read an audio file (with whatever meaning that audio encodes) into a Simulink double() frame . So the question should now perhaps be what kind of input signal is needed by the SDR decoder? If If you have a buffer of Simulink double() signal representing QPSK modulated data, what has to be done to transform that double() vector into something that the SDR QPSK demodulator can use?
  3 Comments
Walter Roberson
Walter Roberson on 24 Jun 2021
If you look at sdruqpskrx() and update diagram, you can see that the output of the SDRu receiver is datatype double. So if you replace the receiver block with something that generates a double signal to pass over to the receiver, then you do not need to be concerned over whether it is a timeseries or not.
QPSK expects complex data, but your .wav file will be real-valued. In such cases it is common for the wav file to have two channels, with the left channel being the real-valued component and the right value being the complex-valued component.
muhammad ahmad
muhammad ahmad on 24 Jun 2021
i am going to try this i will transmit signals using USRP and recieve through RTL SDR

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