serdes.DFE adapttion algorithm in R2023a

Hi sirs,

Matlab function serdes.DFE

DFE.m

line 576~581

%DFE Adaptation

if ModeIsAdapt(obj) && obj.AdaptNextStep

for kk = 1: length(obj.TapWeights)

% update tap

obj.DFEtapInternal(kk) = obj.DFEtapInternal(kk) ...

- obj.EqualizationGain * waveOut(1) * obj.SymbolShiftRegister(kk);

The reference I found for LMS adaptive equalization, waveOut(1) shoud be error, not the output result.

Is there anything I misunderstanding? why matlab code can use waveout instead error?

Thank you for your help.

KC

Answer 1

[Umang Pandey]

Hi @kuang,

The DFE algorithm uses a decision-directed adaptation method. In this method, the output of the equalizer is quantized to the nearest symbol (this is the "decision" part), and this quantized output is used as the desired signal for the adaptation. The error signal is then the difference between this quantized output and the actual output.

But if the output is already quantized to the nearest symbol, then this error signal is zero! So, the DFE algorithm effectively uses the output signal “waveOut(1)” as the error signal for the adaptation.

Thus serdes.DFE function can use “waveOut(1)” instead of the error signal because it is implementing a DFE with decision-directed adaptation, where the error signal is effectively the same as the output signal.

Best,

Umang