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Plot Noisy DVB-S APSK Constellation using Simulink

Apply DVB-S APSK modulation to random data symbols, pass the modulated signal through an AWGN channel, and then plot the signal constellation.

The slex_dvbs_apsk_mod model is configured for the S2 standard suffix and modulation order 16. For you to get desired results, all blocks in the model must align their configuration to the same modulation order. To set the modulation order for the DVBS-APSK Modulator Baseband block, select a value from the dropdown list in the block mask. The set of modulation orders available varies depending on the DVB standard suffix parameter setting. The InitFcn callback defines the workspace variable, M = 16, and this variable is used to set the:

The Constellation Diagram block has the Reference constellation parameter set to Custom and the Custom value parameter set to align with the modulator block's modulation setting. To see the values, open Reference Constellation in the Plot tab on the Constellation Diagram window.

Run the model with the EbN0 of the AWGN channel block set to 20 dB, and then view the constellation diagram.

Change the EbN0 of the AWGN channel block to 10 dB. Run the model and observe the increase in noise shown in the plotted constellation diagram.

You can try running the model with a different modulation order. To adjust the modulation order, you must align the:

  • Modulation order setting in the DVBS-APSK Modulator Baseband block

  • Value of the workspace variable M

  • Reference constellation in the Constellation Diagram block

If these parameters are not aligned with each other, the reference constellation and input signal do not produce the desired constellation.