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Re: [802.3_COM] COM 4.17.0 interference and quantization noise discrepancies with 178A

Hi Jimmy,

Thank you for the review. In 1 you are correct. The function  s21_pkg need to include H_t=1 for
if OP.PSDRXCAL && channel_number == param.num_s4p_files

The effect of H_t filtering is minimal erring on very slightly more added noise. I.e. no false rx passes.

… Rich

From: Zhimin Liang <jimmy.liang@xxxxxxxxxxx>
Sent: Friday, October 23, 2026 8:29 PM
To: STDS-802-3-COM@xxxxxxxxxxxxxxxxx
Subject: [802.3_COM] COM 4.17.0 interference and quantization noise discrepancies with 178A

 

Hi,

 

I noticed some seeming discrepancies between the 4.17.0 COM code and the 802.3dj Draft 3.3 178A. So I wanted to get confirmation, and put attention on them so they can get fixed.

 

1.

Transmitter rise time filter is not applied to interference noise (shown in Figure 178A-8).

But it appears to be applied in the code.

The interference noise uses sdd21p

        %% compute S_in ( eq 178A-24 d0.2 )
        % S_in = 0 when Rx Calibration is not performed
        if OP.PSDRXCAL
            % interpolate to fvec
            result.H_noise=H_interp(chdata(end).sdd21p,chdata(1).faxis,fvec,f_b);

Which has H_t, the transmitter rise time filter, included

        if include_die
            s21p= H_t.*s21.*(1-gamma_tx).*(1+gamma_rx)./(1.- s11.*gamma_tx - s22.*gamma_rx  -s21.*s12.*gamma_tx.*gamma_rx +s11.*s22.*gamma_tx.*gamma_rx);

2.

When quantization noise is added the cursor is skipped in the code

    if irxffe ~= cursor_tap
        quantization_noise_in_pdf_scale = scalePDF(quantization_noise_in_pdf, abs(h_rxffe(irxffe)));
        quantization_noise_pdf = conv_fct(quantization_noise_pdf, quantization_noise_in_pdf_scale);
    end

But the draft says to use all the taps

"The probability distribution function for the quantization noise at the detector input pqn(y) is initialized to a

Dirac delta function and the assignment defined by Equation (178A–46) is repeated for each value n in the

feed-forward filter tap index vector i (i.e., over all of the feed-forward filter coefficients)."

 

3.

Vqc is defined as

"the quantization clipping amplitude Vqc is a positive value that satisfies the relationship Psn(–Vqc) = Pqc / 2"

But the code does not divide by 2

adc_clip = -CDF_inv_ev(param.P_qc, sig_after_ctle_pdf, sig_after_ctle_cdf);

 

Jimmy

 

 

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