Constellation not visisble after DUC?

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)

I am getting a proper constellation after the Fiilter block (as you can see in the image below)

But after the DUC unit, i am getting something

The spectrum i am getting afetr both the stages are shown below

After Root Cosine

After DUC unit

In the image below, we can see the DUC block setting

Please help me to resolve this issue.

Regards

Amol

Answer 1

[Navya Seelam]

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.