Re: [10GBT] Issues with solarsep_varlen7a.m
Sailesh,
Thanks for providing this information. We've had always some doubts abt this
program. Can u please provide a modified code, so that we can have a look at
that before the meeting?
rgds,
Samir.
----- Original Message -----
From: "sailesh rao" <sailesh_rao@HOTMAIL.COM>
To: <STDS-802-3-10GBT@LISTSERV.IEEE.ORG>
Sent: Wednesday, July 07, 2004 12:33 PM
Subject: [10GBT] Issues with solarsep_varlen7a.m
> George/Carlos,
>
> I would like to bring up some issues with the solarsep_varlen7a.m matlab
> code that is found on
>
> http://grouper.ieee.org/groups/802/3/an/public/material/index.html
>
> I believe that these issues alter the conclusions that one could derive
from
> this code.
>
> 1. Frequency Base:
> The frequency base for the DFE margin calculations is being inferred from
> the first column in the Insertion Loss files found in this directory. As a
> result, the frequency base ranges from 0 to 650MHz in all cases. However,
> the average power P is being distributed evenly over (line 391)
>
> bwmhz=1250MHz for the 2-bit PAM system,
>
> bwmhz=1000MHz for the 2.5-bit PAM system,
>
> bwmhz=833MHz for the 3-bit PAM system
>
> This means that 48% of the input power is unused in the 2-bit system, 35%
is
> unused in the 2.5-bit system and only 22% is unused in the 3-bit system.
> This tips the scale in favor of the 3-bit PAM system.
>
> 2. Folded SNR calculation:
>
> The folded SNR calculations in lines 443, 453 and 463 are not right. If f1
> and f2 are mirror frequencies about fs/2, the formula being used is
>
> S/N = ABS(S1/N1) + ABS(S2/N2) ;
>
> However, the actual SNR at the folded frequency would be
>
> S/N = ABS(S1+S2)/ABS(N1+N2)
>
> where S1, S2, N1, and N2 are complex phasors. Therefore, in the context of
> folding, the actual PSD of the signal becomes relevant, whereas the
original
> Salz formula for the optimum DFE SNR is independent of the PSD.
>
> As done in the matlab code, this calculation also tips the scale in favor
of
> the 3-bit PAM system since signal power is assumed to be zero for f>650MHz
> due to (1) above.
>
> 3. SNR Requirement for 1E-12 BER
>
> The SNR requirement for 2.5bit PAM is 3.01dB worse than the SNR
requirement
> for 2-bit PAM.
> The SNR requirement for 3bit PAM is 6.23dB worse than the SNR requirement
> for 2-bit PAM.
>
> The code is using 2.95dB and 5.94dB respectively in lines 446, 456 and
466,
> which also tips the scale in favor of the 3-bit PAM system.
>
> Regards,
> Sailesh Rao.
>
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