I would like to see the constellation diagram after equalization as shown in the website Correct constellation for QAM. But I am getting a different plot. Can somebody please tell me where I am going wrong?

after equalization


1 Answer 1


You are getting the correct constellation. You need to remember that you added noise to your symbols in the channel, So, you won't get a perfect constellation as you have in the first figure. Try increasing SNR (EbNo) and you will see better the constellation.

This is what I got:

enter image description here

  • $\begingroup$ Thank you for the explanation. Could you please say in general, the reason after equalization, the constellation diagram contains a cluster of symbols but in the actual constellation there isn't. What I mean to say is what do the cluster of points represent and then there are some stray points as well after equalization? $\endgroup$
    – SKM
    Commented Nov 21, 2015 at 23:40
  • $\begingroup$ Because you add noise to your signal. So, in the receiver what you get is the symbols plus noise. The noise makes this cluster appear around the value of the actual symbol. You can find more information about this in any Digital Communication book. $\endgroup$
    – JohnMarvin
    Commented Nov 23, 2015 at 10:20

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