Re: [10GBT] Request for Cat6 Emissions Characteristics
Jose,
It is interesting to note that your frequency range of interest has now
narrowed down to "in the range of 200MHz".
Frankly, I think you are being too cavalier about the peaky PSDs in the
PAM12 proposal in the 200MHz-300MHz frequency range. Given the peaky PSDs at
the start of each frame in your proposal (i.e., once every 52,833 bits), I'm
afraid that at 10Gb/s these peaks occur often enough for the FCC to become
very interested in them.
If you now think that you will "scramble the frame start bits", may I ask
why you didin't think of this scrambling last month? It is blatant omissions
like these that can sink a standard.
Regards,
Sailesh Rao.
srao@phyten.com
>From: Jose Tellado <JTellado@TERANETICS.COM>
>Reply-To: "IEEE P802.3an" <STDS-802-3-10GBT@listserv.ieee.org>
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
>Date: Fri, 23 Jul 2004 23:40:25 -0700
>
>
>Sailesh,
>
>As Glenn described, when you corrected spectra.m (which improved PAM12)
>you did eliminate your original "EMI PSD" plots.
>
>We all understand that EMI is a complicated problem and hopefully it's
>not an issue, but I don't think you should omit results that can be
>useful to the group to evaluate. Attached is your revised code with all
>four plots included (I just had to copy from your original code) plus
>the FCC and CISPR EMI shapes.
>
>Based on your corrected code and the EMI limits you provided, it appears
>that the most problematic region is around 200MHz and in this area PAM12
>is up to 1dB better,
>
>Jose
>
>
>PS On the peaky PSD issue, the sync pattern highest peak is 23dB below
>the signal PSD. This adds about 0.02dB of ripple. I don't think test
>equipment can even measure this. But if you think this ripple is too
>high we can always scramble it :)
>
>10*log10(1 + 10^(-23/10)) = 0.0217 dB
>
>
>
>
>-----Original Message-----
>From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
>Behalf Of sailesh rao
>Sent: Friday, July 23, 2004 10:03 PM
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
>
>Glenn,
>
>There are several reasons I stated for why this calculation is
>incorrect.
>
>1. In the passband (upto ~0.25fs), where we can do nothing about the
>transmit PSD, PAM12 is 0.8dB higher than PAM8. This is the killer
>portion of the frequency band as far as emissions are concerned, since
>we can filter out the higher frequencies without incurring much penalty
>in the receiver performance.
>2. You appear to be focusing on a narrow region of the frequency band
>above 200MHz. If you are concerned with this narrow frequency band,
>please note from the attached that the FCC and CISPR limits increase in
>that frequency band. These changes in limits should be taken into
>account in any such "peak EMI PSD" calculations that you are doing. The
>reason I deleted this portion of my matlab code was because I didn't
>have the exact frequencies at which these steps occur, and I didn't want
>to make another mistake and provoke another round of highly
>disrespectful e-mails on the reflector.
>3. Emissions optimizations cannot be done by just doing some 20log10
>calculations on average PSDs and selecting the system that shows the
>lowest peak. For instance, the PAM12 proposal uses periodic frame start
>symbols that have "peaky" PSDs (see, e.g., the PSD "bumps" on slide 26
>of tellado_1_0704.pdf). You are guaranteed to get much higher peaks in
>the 200-300MHz range for the PAM12 proposal because of the addition of
>these PSD bumps. Therefore, just looking at the average PSD is
>insufficient for "estimating" emissions.
>
>In any case, the PAM12 EMI penalty is well over 4dB for existing
>cabling.
>This is a huge hole that the PAM12 proponents are trying to climb out
>of, and I don't see how we can go before IEEE 802.3 and claim
>
>1. 10GBASE-T is an extremely hard problem, which requires the 10GBASE-T
>PHY solution to operate very close to the Shannon limit.
>2. The task force decided to choose PAM12 that has a 4dB EMI penalty
>over PAM8, because the task force decided that these 4dBs are not that
>important.
>
>(2) contradicts (1) and therefore, don't you think that we will get our
>clocks cleaned at the working group level?
>
>Regards,
>Sailesh Rao.
>srao@phyten.com
>
>
>That is a completely untenable
> >From: Glenn Golden <gdg@zplane.com>
> >Reply-To: gdg@zplane.com
> >To: STDS-802-3-10GBT@listserv.ieee.org
> >Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
> >Date: Fri, 23 Jul 2004 21:24:32 -0600
> >
> >
> >On Thu, 22 Jul 2004 16:07:12 Sanjay Kasturia wrote:
> > >
> > > This makes me doubt the objectivity of your analysis.
> > >
> >
> >
> >On Thu, 22 Jul 2004 16:52:22 "Kardontchik, Jaime" wrote:
> > >
> > > I would suggest to delete the remark about "objectivity".
> > > It is really unwarranted.
> > >
> > > Everyone is trying to do the best possible technical analysis in
> > > real-time.
> > >
> > > It happens that the ones that dare offer their code for public
> > > scrutiny in order to advance the discussions, end up being
> > > criticized for the incompletness, inaccuracies, etc, of their code.
> >
> >
> >I'm not sure that Sanjay's remark had to do with Sailesh's program
> >having a bug. Everyone understands that honest mistakes of this sort
> >will occasionally be made, and that public stonings on the reflector
> >are not appropriate. I think Sanjay's remark may have had to do with
> >what happened after the error was pointed out and corrected.
> >
> >In his original posting (based on the computations prior to the bug
> >fix) Sailesh showed four plots: Two large scale, and also two zoomed-in
>
> >"EMI PSD" plots. Only the latter two include the 20log(f) radiated
> >emission frequency dependence, which, in past postings, Sailesh himself
>
> >has specifically pointed out as being relevant to EMI considerations.
> >On those zoomed-in plots, he made a point of noting that the
> >differential between the PAM8 and PAM12 peaks was trivial:
> >
> > >
> > > In both cases, the peaks for the so-called "EMI PSD"s are within
> > > 0.01dB of each other for PAM8 and PAM12.
> > >
> >
> >But in the subsequent posting, after the bug was fixed, the zoomed-in
> >EMI PSD plots with the 20log(f) factor were omitted, and nothing was
> >said about the relationship between the PAM8 and PAM12 peaks. This
> >omission was justified with the following dismissive comment:
> >
> > > Besides, in any case, the FCC limits for emissions increases in the
> > > neighborhood of 220MHz, thereby rendering Jose's emissions
> > > contentions completely irrelevant.
> >
> >and later
> >
> > > I consider the point Jose made about the emissions issue to be pure
> > > specmanship, and I've already stated that it is completely
>irrelevant.
> >
> >I think Sanjay's response probably had to do with the lack of clear
> >technical basis with this claim was made, and with the curious way that
>
> >plots which had been relevant prior to the bug fix became "totally
> >irrelevant" after it was corrected, since the actual plots -- had they
> >been included in the posting -- do not seem to support that contention.
> >
> >The plots are attached, along with original (erroneous) plots:
> >
> > 7525_orig.gif 0.75_0.25D filter, original (erroneous)
>results
> > 7525_corr.gif " " corrected results
> >
> > unger_orig.gif Ungerboeck filter, original (erroneous)
>results
> > unger_corrected.gif " " corrected results.
> >
> >These were produced using the original and corrected spectra.m programs
>
> >respectively, with changes made only to the axis limits so as to focus
> >in on the claims being made about the behavior near the peaks.
> >
> >In the corrected EMI PSD plots -- the ones that incorporate 20log(f)
> >and were omitted from Sailesh's second posting -- even if one
> >completely ignores the energy above 216 MHz [I think that's where the
> >actual Part
> >15 mask breakpoint is] PAM12 has a lower peak value for both filters.
> >For the Ungerboeck design, both peaks occur below 216 MHz, and the peak
>
> >differential -- which Sailesh was interested in pointing out earlier
> >when his numbers were wrong and showed no penalty for PAM8 -- is now
> >0.8 dB in favor of PAM12.
> >
> >So, as far as the actual data at hand goes, it seems disingenuous to
> >use the step in the EMI mask as justification for dismissing Jose's
> >claim as "totally irrelevant", when in fact for one of the filters, it
> >supports exactly the opposite conclusion.
> >
> >It may well be true that when the smoke clears on this issue, neither
> >system is significantly different as regards peak EMI. But the present
>
> >data does not make that case, and dismissing it with a verbal flourish
> >does not help to advance the discussion.
> >
> >
> >Glenn Golden
> >Principal Engineer
> >Teranetics, Inc.
> >ggolden@teranetics.com
> >
> ><< unger_corrected.gif >>
> ><< unger_orig.gif >>
> ><< 7525_corr.gif >>
> ><< 7525_orig.gif >>
>
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><< EMIPSDSaileshCode.pdf >>
><< spectraAllPlots.m >>
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