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*To*: STDS-802-3-10GBT@LISTSERV.IEEE.ORG*Subject*: [10GBT] Issues with solarsep_varlen7a.m*From*: Sailesh Rao <saileshrao@OPTONLINE.NET>*Date*: Wed, 7 Jul 2004 14:58:54 -0400*Approved-By*: bradley.booth@INTEL.COM*Importance*: Normal*Reply-To*: "IEEE P802.3an" <STDS-802-3-10GBT@LISTSERV.IEEE.ORG>*Sender*: stds-802-3-10gbt@IEEE.ORG

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.
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.
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.
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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