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Re: [10GBT] Request for Cat6 Emissions Characteristics



Folks,

This gets worse. A closer reading of tellado_1_0704.pdf reveals that fixed
patterns are being sent once every microsecond on all 4 wire pairs
simultaneously!

Talk about peaky PSD bumps in the PAM12 transmit spectra, yikes!

Regards,
Sailesh Rao.
srao@phyten.com

>From: sailesh rao <sailesh_rao@HOTMAIL.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: Sat, 24 Jul 2004 15:10:58 -0400
>
>Seki,
>
>I disagree that the "ripple is small". If we keep sending the same pattern
>over and over, once every MHz, the ripple won't be small. It is technically
>incorrect to pretend otherwise.
>
>Heck, I have a good mind to add a large number of dBs to the PAM12 Total
>EMI
>penalty to account for this problem.
>
>In HDSL2, the frequencies were too low to cause any emissions concerns.
>
>Regards,
>Sailesh Rao.
>srao@phyten.com
>
>>From: "K. Seki" <k_seki@MTC.BIGLOBE.NE.JP>
>>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: Sat, 24 Jul 2004 18:05:04 +0900
>>
>>Sailesh,
>>
>>As Jose mentioned, PAM12 has 1dB lower EMI PSD around 200MHz than PAM8,
>>even if adding 0.02dB of ripple.
>>I am not expert on EMI, but I don't think that the ripple have meaningful
>>effect on EMI,
>>becuse the ripple is very small.
>>Furthermore, HDSL2 have already applied a similar PAM2 frame alignment
>>method.
>>I would appreciate any input from the EMI experts.
>>
>>Regards,
>>Seki
>>
>>-----Original Message-----
>>From: sailesh rao <sailesh_rao@HOTMAIL.COM>
>>Sent: Sat, 24 Jul 2004 03:23:39 -0400
>>Subject: 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 >>
>> >
>> >_________________________________________________________________
>> >Overwhelmed by debt? Find out how to 'Dig Yourself Out of Debt' from MSN
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>> >
>> ><< EMIPSDSaileshCode.pdf >>
>> ><< spectraAllPlots.m >>
>>
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