[wireless waveform generator] how to read its Constellation Diagram

i'm trying the wireless waveform generator and find difficult to understand the Constellation Diagram.

For example I generate waves of 1 non-HT packet using MCS4 (screenshot of settings shown below), get the Constellation Diagram (again attached below). I expected to see yellow dots scattering near the reference points (red-color cross), but I did't see it.

Is my expectation right? If yes, what should I do to see it?

If not, how to read the Constellation Diagram?

Thx.

Answer 1

[Parag]

Hi @Xiaolei,

Your expectation is valid — when generating a waveform using MCS4 (16-QAM, rate 1/2), you should ideally see the received constellation points (yellow dots) clustered around the reference 16-QAM positions (red crosses).

However, the scatter you're currently seeing occurs because the constellation diagram is likely being plotted before demodulation and equalization. At that stage, the raw waveform still includes impairments like channel effects, noise, and phase distortions, which cause the constellation points to appear scattered and not aligned with the ideal reference.

To see the expected clustering around the reference points:

You need to apply receiver processing, which includes:

• OFDM demodulation
• Channel estimation
• Equalization

This can be done either:

1. Within the Wireless Waveform Generator App, if there is an option to apply receiver processing or visualize the constellation after equalization.
2. Programmatically, using MATLAB functions like “wlanNonHTDataRecover” which process the waveform and output demodulated, equalized symbols for accurate constellation plotting.

Once the signal is properly processed, the yellow constellation points will cluster correctly around the red crosses, representing the ideal 16-QAM constellation.

Please refer to following MATLAB documentation for more information about “wlanNonHTDataRecover”:

https://www.mathworks.com/help/wlan/ref/wlannonhtdatarecover.html

Hope this is beneficial!