MATLAB Answers

Constellation not visisble after DUC?

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Amol bhindwale
Amol bhindwale on 25 Dec 2019
Answered: Navya Seelam on 2 Apr 2020
I am trying to simulate a system in Simulink, where i am trying to generate a QPSK modulated waveform (As you can see in the image below)
Screenshot from 2019-12-25 20-50-07.png
I am getting a proper constellation after the Fiilter block (as you can see in the image below)
Screenshot from 2019-12-25 20-53-08.png
But after the DUC unit, i am getting something
Screenshot from 2019-12-25 21-00-25.png
The spectrum i am getting afetr both the stages are shown below
After Root Cosine
Screenshot from 2019-12-25 21-05-20.png
After DUC unit
Screenshot from 2019-12-25 21-06-08.png
In the image below, we can see the DUC block setting
Screenshot from 2019-12-25 21-10-34.png
Please help me to resolve this issue.
Regards
Amol

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Answers (1)

Navya Seelam
Navya Seelam on 2 Apr 2020
Digital Up-Converter block converts a complex digital baseband signal to a real passband signal. Since the output of DUC block is real you are getting such constellation. You will get the expected QPSK contellation when you down convert the output of DUC.

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