Re: [10GBT] PAM12 performance
Thanks for the clarification.
I appreciate your concern for implementation issues. Ultimately the chips will land on PC boards with switching power supplies, clock distribution, high-frequency I/O busses, and imperfections that will make layout challenging. I too am concerned about some of the less tangible elements that are hard to quantify in a traditional signal analysis.
All that said, I also have concerns about pragmatic need to make forward progress on the standard. I hope that the task force can fully digest these alternatives and make a good decision that allows progress to be made. I believe that lack of forward movement at the October meeting will effectively be a step backward as the glide slope for a UTP market opportunity is closing because fiber alternatives continue to drop in cost.
> -----Original Message-----
> From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG]On
> Behalf Of sailesh rao
> Sent: Tuesday, August 24, 2004 6:20 PM
> To: STDS-802-3-10GBT@listserv.ieee.org
> Subject: Re: [10GBT] PAM12 performance
> Scott is referring to theoretical comparisons of SNR margins based on
> hypothetical PAM8 and PAM12 systems, operating under
> worst-case conditions.
> These SNR margins are computed relative to the separation of
> levels at the
> receiver output.
> I am referring to the EMI susceptibility margin that is computed with
> respect to the amplitude of the noise at the input that can
> be tolerated by
> the receiver in an EMI range test.
> In any case, as was pointed out in a response to Hugh Barass
> (and Scott
> Powell), even this "slight" theoretical SNR margin advantage
> that Scott
> claims for PAM12 does not apply to the proposal on the table,
> due to the
> issues 3 through 5 that I listed in my summary e-mail.
> With respect to the implementation advantage for PAM12, it is
> correct that
> the 15% reduction in clock rate is helpful. However, on the
> flip side, the
> PAM12 receiver requires 3.9dB higher SNR at the output, which
> implies that
> the analog front end glitches and other AFE implementation
> noises must be
> kept 3.9dB lower for the PAM12 receiver. In my engineering
> judgement based
> on considerable lab experience with such AFE issues for a much simpler
> problem, 1000BASE-T, the latter disadvantage strongly
> outweighs the former
> advantage, thus rendering PAM12 much more difficult to
> implement than PAM8.
> >From: "Dove, Dan" <dan.dove@HP.COM>
> >Reply-To: "IEEE P802.3an" <STDS-802-3-10GBT@listserv.ieee.org>
> >To: STDS-802-3-10GBT@listserv.ieee.org
> >Subject: Re: [10GBT] PAM12 performance
> >Date: Mon, 23 Aug 2004 12:01:42 -0700
> >Scott, Sailesh;
> >Can I ask for a little help here? I am having a hard time with the
> >following two phrases.
> >Scott says;
> > > At the risk of repeating myself, none of this changes the
> > > fundamental fact
> > > that it has been clearly shown that the PAM-8 and PAM-12
> > > proposals have
> > > similar performance (slight edge for PAM-12), but the PAM-12
> > ^^^^^^^^^^^^^^^^^^^^^^^^
> > > proposal offers
> > > the advantage of a reduced operating frequency resulting in
> > > reduced power
> > > and reduced implementation difficulties.
> >Sailesh says;
> > > a). PAM8 has 3.9dB better susceptiibilty penalty than PAM12
> > > over a 0m cable.
> > > b). PAM8 has 3.2dB better susceptibility penalty than PAM12
> > > over a 55m Cat-6
> > > cable (existing Cat-6 cabling), c). PAM8 has 2.0dB better
> > > susceptibility
> > > penalty than PAM12 over a 100m Cat-6 cable (new Cat-6 cabling).
> >Dan reads;
> >PAM12 is slightly better than PAM8, but PAM8 is at least
> 2.0dB better than
> >Even worse, that difference could be substantial if we are close to a
> >regulatory or functional limit.
> >Please... for those of us who really don't like conundrums, would you
> >figure out a way to come to an agreement on the numbers?
> Either one is
> >better, or the other, but both can't be "better than the other".
> >If it turns out that PAM8 has better theoretical
> performance, but PAM12 is
> >easier implemented and more likely to engender broad support... I can
> >understand that. But both having better performance is too
> puzzling for me.
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