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Re: [10GBT] Summary of issues with PAM12


I will let others speak for themselves but the main reason I prefer
12PAM over 8PAM is the ~10% to 20% lower symbol rate which will reduce
the speed requirements for the AFE and the clock speed requirements for
the digital signal processing.

I think the lowering of the symbol rate can be done with no significant
margin penalty.

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-----Original Message-----
From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
Behalf Of sailesh rao
Sent: Friday, August 20, 2004 8:33 AM
Subject: Re: [10GBT] Summary of issues with PAM12


With regard to issues 1 and 2, I don't believe that there are any
disputes about my calculations. I've already addressed these so-called
disputes in my summary e-mail and pointed out why my analysis stands.

With regard to issue 3, firstly, the main rationale advanced by the
PAM12 proponents for their 3bits/baud scheme is that it has 0.7dB higher
Salz SNR margin over the 2.5bits/baud scheme used in PAM8, over a 100m
However, once you put a hole in the constellation and throw away at
least 1.1dB, would you now concede that this rationale is technically
invalid, and that the Salz SNR margin advantage also swings to PAM8 over
PAM12 at ALL cable lengths, from 0m to 100m?

Secondly, the hole in the constellation makes the PAM12 transmit PSD a
function of the THP coefficients. Therefore, every time a system vendor
finds that the system violates emissions limits, we can expect him/her
to demand to examine the THP coefficients of the PHY, if this task force
standardizes PAM12.

Thirdly, the  hole in the constellation makes the receiver SNR margin a
function of the THP coefficients of the alien neighbors.

With regard to issue 5, please check the details on the PAM8 proposal.
You will see that there are NO fixed patterns used anywhere to delineate
data frames or anything. Therefore, it is not "necessary" to use fixed
patterns for this purpose. These fixed patterns waste the precious
Shannon capacity which the cabling community is working hard to provide
us, though not on the same scale as the other issues with the PAM12
proposal, and which is why I listed this issue last.

Sailesh Rao.

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