DVB-S2 HDL Receiver: frequency synchronization does not working properly

Hi everyone,

I am trying to run the standard "DVB-S2 HDL Receiver" example from the Satellite Communications Toolbox. I am using the exact default parameters provided in the example documentation without any modifications.

• Example Reference: DVB-S2 HDL Receiver
• MATLAB Versions Tested: R2023a and R2024b / R2025b

The Issue:Even after letting the simulation run for a significant duration, the displayed constellation diagram in both scopes (Constellation Plots1 and Constellation Plots2) shows a persistent spinning/ring shape. This indicates a significant remaining frequency offset that is not getting locked or fully corrected by the receiver's carrier synchronization loop.

Additionally, I noticed that the "Estimated Frequency Offset" display fluctuates heavily and fails to settle or converge to a stable value throughout the simulation.

The simulation also does not output or show the extracted data in a scop as demonstrated in the example documentation.

I have attached a screenshot of the Spectrum Analyzer and the two Constellation Plots showing the behavior.

Questions:

1. Is this the expected behavior for the default channel settings in this example, or should the synchronization loop converge to the red reference crosses (QPSK/8PSK points)?
2. Are there specific tuning parameters (such as the loop bandwidth or gains inside the frequency estimation/carrier recovery blocks) that I should modify to help the HDL receiver model achieve a stable lock?
3. Has anyone else encountered this convergence issue in recent MATLAB releases, and how did you resolve it?

Thank you in advance for your help!

[Karthik Akula]

The Synchronized Data Symbols will show constellation. The symbol synchronized symbols remain a circle.

I see the display shows 5.017e5 = 501.7e3. as input is 500e3, the left over frequency is 1.7e3 = 1700. and the model in it's default position is ran for 53%. Can you run until the end and send the snap shot with the "view diagnostics" at the bottom of the model. The verification script auto runs , if nothing is modified.