Re: [10GBT] Updated Tables
Vivek,
I fully agree with you, when comparing PAM12 and PAM8, we should
decouple the number of PAM levels from the LDPC performance. For a more
"fruitful" comparison we should all use the same LDPC code, with the
same latency and coding gain.
It's not fair to compare a PAM12+LDPC_1 with a PAM8+LDPC_2 code when the
PAM8+LDPC_2 code has almost twice the latency.
Amir volunteered to have a separate list to compare LDPC codes on their
own merits, please let's not confuse LDPC gain with PAM gain.
I totally agree with Sailesh's comment below:
"The bottom line is that the PAM8 modulation scheme is not wedded to a
specific Djurdjevic LDPC code and we should really dis-associate the
specific LDPC code choice from the choice of PAM levels. For instance,
the PAM8 proposal will work just fine with the (1024,833) code the PAM12
proponents are using"
Given that the only code with simulation results down to 1e-12 BER is
the (833,1024) I would suggest we use it for comparing PAM12 and PAM8.
But if somebody objects, we can use the coding gain of any other good
LDPC code as a reference, as long as it has reasonable latency and gain
and proven performance around 1e-12.
Jose
-----Original Message-----
From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
Behalf Of Vivek Telang
Sent: Monday, July 19, 2004 5:59 PM
To: STDS-802-3-10GBT@listserv.ieee.org
Subject: Re: [10GBT] Updated Tables
Sailesh,
In that case, to simplify comparisons, I propose that we decouple the
line code variable from the analysis, and assume the same coding gain
for both line codes.
I believe the coding gain assumed in Scott's presentation was 10.0 dB
(33.8-23.8), so shall we say that the PAM-8 SNR required for BER=1e-12
is 30.3-10 = 20.3 dB?
Vivek
-----Original Message-----
From: stds-802-3-10gbt@ieee.org [mailto:stds-802-3-10gbt@ieee.org]On
Behalf Of sailesh rao
Sent: Monday, July 19, 2004 6:11 PM
To: STDS-802-3-10GBT@listserv.ieee.org
Subject: Re: [10GBT] Updated Tables
Vivek,
Thanks for the opportunity.
At the meeting, Jose pointed out that the extension of the SNR/BER curve
I made on the (2048,1723) code from 6E-11 BER down to 1E-12 BER (slide
10 of
rao_1_0704.pdf) was not based on real simulations. I had assumed that
the
1E-12 BER assertions on slide 4 of seki_1_0304.pdf was based on real
simulations, but it was apparently just a "hand extrapolation" of my
original SNR/BER curve. Unfortunately, this point was not clarified to
me during my e-mail correspondence with Dr. Seki.
At the moment, I stand by the 6E-11 BER point in the BER vs. SNR curve
of the (2048,1723) LDPC code since I personally supervised the
generation of this simulation point. In the worst-case, assuming
Murphy's law applies, we can expect the BER/SNR curve for the
(2048,1723) LDPC code to undertake a slope change in parallel with the
uncoded Gaussian curve and the intercept for the 1E-12 BER will occur
slightly higher than 19.9dB (my extrapolation shows 20.4dB, not 20.9dB).
However, this is a moot point. If Amir Mezer's LDPC simulations show
that the (2048,1723) LDPC code has a slope change at 6e-11 BER, I will
instantly recommend adding a row to the Djurdjevic construction for the
(2048,1723) code and pushing the slope change down below the 1E-12 BER
point. Or, for that matter, if Amir Mezer's simulations show that the
(992,829) LDPC code has no slope change until 1E-12 BER, I will
recommend we switch to that code. I am aware that Amir Mezer has close
to infinite computing resources since he is employed at Intel (Amir, I
hope things haven't changed!!!), and therefore, we can rely on him to
validate the specific LDPC code the task force is using down to 1E-12
BER and beyond.
The bottom line is that the PAM8 modulation scheme is not wedded to a
specific Djurdjevic LDPC code and we should really dis-associate the
specific LDPC code choice from the choice of PAM levels. For instance,
the
PAM8 proposal will work just fine with the (1024,833) code the PAM12
proponents are using, though I would personally hesitate to add such a
SONET-on-Steroids like framing complexity in an Ethernet standard. Heck,
we had interoperablilty problems with the scrambler definition on
1000BASE-T - do we really want to deal with interoperability issues with
such a complex framing scheme in 10GBASE-T?
Regards,
Sailesh Rao.
srao@phyten.com
>From: Vivek Telang <vivek@VITESSE.COM>
>Reply-To: "IEEE P802.3an" <STDS-802-3-10GBT@listserv.ieee.org>
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: Re: [10GBT] Updated Tables
>Date: Mon, 19 Jul 2004 16:17:39 -0500
>
>Hi Sailesh,
>
>At the meeting last week, there was a question raised (by Jose) about
>the
>PAM-8 SNR requirement of 19.9 dB for BER=1e-12 (column 3 of your
>table). I think he said that it was actually ~1dB worse than that
>(~20.9dB), but I'm not positive. There was a discussion, but I don't
>think the matter got resolved, so can you clarify?
>
>Thanks,
>
>Vivek
>
>-----Original Message-----
>From: stds-802-3-10gbt@ieee.org [mailto:stds-802-3-10gbt@ieee.org]On
>Behalf Of sailesh rao
>Sent: Monday, July 19, 2004 2:02 PM
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: [10GBT] Updated Tables
>
>
>10GBT'ers:
>
>In the attached, I've updated the 3 tables in our July presentation
>based on the following:
>
>1. Change PAM12 symbol rate to 825Ms/s from 820Ms/s.
>2. Delete PAM10 entry.
>3. As Luc pointed out, add a 1.2dB emissions penalty for PAM12 due to
>its higher transmit PSD.
>4. As Jose pointed out, subtract 0.4dB from the PAM12 emissions penalty
>due to the THP peak voltage adjustment.
>
>Next, I integrated the WGN for 1E-12 BER over the Nyquist frequency
>range to get a "wideband noise tolerance" measure for the two
>proposals. Finally, I summed the noise immunity penalty and the
>emissions penalty for the PAM12 proposal to form a "Total EMI Penalty"
>metric over the PAM8 approach.
>
>In Models 1 and 3, the penalty works out to be 2.6dB and 2.2dB
>respectively for PAM12 over PAM8. However, in Model 2, which represents
>the existing cabling infrastructure, the penalty for PAM12 over PAM8
>works out to a whopping 4.0dB!!
>
>Regards,
>Sailesh Rao.
>srao@phyten.com
>
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