Error in example comm/Decis​ionFeedbac​kEqualizeB​PSKModulat​edSignalEx​ample

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Nicholas
Nicholas 2025-1-17
评论： Voss 2025-1-22
In the example comm/DecisionFeedbackEqualizeBPSKModulatedSignalExample the following line:
eqdfe_lms = comm.DecisionFeedbackEqualizer('Algorithm','LMS', ...
'NumForwardTaps',8,'NumFeedbackTaps',5,'StepSize',0.03);
Needs to read:
eqdfe_lms = comm.DecisionFeedbackEqualizer('Algorithm','LMS', ...
'NumForwardTaps',8,'NumFeedbackTaps',5,'StepSize',0.03, ...
'Constellation', pskmod(0:1, 2));
This is because the default for comm.DecisionFeedbackEqualizer seems to be QPSK not BPSK.
Also the line above it:
bpsk = comm.BPSKModulator;
Is deprecated, it can be changed to:
bpsk = @(x) pskmod(x, 2);

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回答（1 个）

Vinay
Vinay 2025-1-20
Hi @Nicholas Destefano,
The "Decision Feedback Equalizer" uses the QPSK as the default constellation and can be seen by the constellation pattern containing 4 signals defined as
Constellation: [0.7071 + 0.7071i -0.7071 + 0.7071i -0.7071 - 0.7071i 0.7071 - 0.7071i ]
The BPSK signal can be created by providing the argument as
% Real axis constellation BPSK diagram
'Constellation' = pskmod(0:1,2);
The function "comm.BPSKModulator" can be replaced by the "pskmod" as per the modulation technique.
Kindly refer to the below documentaton of "Decision Feedback Equalizer" for more details
https://www.mathworks.com/help/comm/ref/comm.decisionfeedbackequalizer-system-object.html
I hope this resolves the query!
  2 个评论
Nicholas
Nicholas 2025-1-22
Apologies if I wasn't clear. I understand how to add the constellation to the equalizer, as I mention it in my comment.
It appears that the MATLAB example code itself is incorrect, specifically comm/DecisionFeedbackEqualizeBPSKModulatedSignalExample. Since it's a small example, with no plots, it's not easy to notice.
I don't know how to make suggestions to improve MATLAB's examples. Is there another place to do that?
Voss
Voss 2025-1-22
"I don't know how to make suggestions to improve MATLAB's examples. Is there another place to do that?"
@Nicholas Destefano: At the bottom of the documentation page, there is a text prompt ("How useful was this information?") with five stars you can click on to provide feedback.

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