Re: [10GBT] Request for Cat6 Emissions Characteristics
Sailesh,
There must be something wrong with the code, when the integral of the
1GBaseT PSD power is 15dBm (details below).
I thought I gave you a good hint, and I rather you debug your code.
The problem is likely in your modeling of the digital/analog sampling
rate conversion, lines 12-35.
You can check the 3rd chapter of (or any other introductory DSP book):
Oppenheim and Shafer, "Discrete Time Signal Processing". It's eq (3.49)
in my undergrad international edition.
Jose
1GBase-T power details:
10*log10(sum(10.^((f5mag-116)/10)))+60 = 15.3dBm
This equation computes the (discrete) integral of the PSD, where
(f5mag-116) is the PSD from your code, and 60dB converts from MHz to Hz.
-----Original Message-----
From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
Behalf Of sailesh rao
Sent: Wednesday, July 21, 2004 3:29 PM
To: STDS-802-3-10GBT@listserv.ieee.org
Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
Jose,
Please point out which lines in the matlab code I distributed,
spectra.m, have "bugs".
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: Wed, 21 Jul 2004 12:14:42 -0700
>
>Sailesh,
>
>It appears you have a bug in your program. You are assuming that PAM12
>is transmitting 0.8dB more power than PAM8 which is unfair. When you
>correct for this PAM12 should have better EMI.
>
>Jose
>
>Details:
>
>When I compute the total power transmitted for the PAM8 case by
>integrating the PSD I get 4.1dBm
>
>10*log10(sum(10.^((f8mag-116)/10)))+60 = 4.1dBm
>
>But when I compute the total power tx for the PAM12 case I get 4.9dBm
>
>10*log10(sum(10.^((f12mag-116)/10)))+60 = 4.9dBm
>
>
>PS. You probably made a mistake in the Butterworth filtering sampling
>rate adjustment or in a amplitude/power log mix-up.
>
>
>-----Original Message-----
>From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
>Behalf Of sailesh rao
>Sent: Wednesday, July 21, 2004 9:37 AM
>To: STDS-802-3-10GBT@LISTSERV.IEEE.ORG
>Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
>
>Jose,
>
>It turns out that when you take into account the analog filtering and
>do an accurate calculation of the PSD/"EMI PSD", neither PAM8 nor PAM12
>has an advantage in terms of EMI. I'm attaching the PDF ouput and the
>matlab code to generate the PSDs using both Ungerboeck's analog filter
>construction (3rd order BW LPF at fs/4) and using the (0.75+0.25D)
>approach used in our July presentation (with 5th order BW LPF at fs/2).
>In both cases, the peaks for the so-called "EMI PSD"s are within 0.01dB
>of each other for PAM8 and PAM12.
>
>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: Wed, 21 Jul 2004 00:06:30 -0700
> >
> >
> >
> >
> >All,
> >
> >From talking to several 10GBase-T EMI experts, the general consensus
> >is
>
> >that EMI emissions increase with frequency as 20*log10(f).
> >
> >Thus the system with the higher symbol rate (PAM8 at 1000MHz) will
> >have
>
> >worse EMI if the tx power is the same and both have equivalent
> >digital and analog filtering.
> >
> >The plot below shows the EMI PSD for 1GBase-T, PAM12 and PAM8
> >assuming all have the same digital filter 3/4+1/4D. As expected the
> >PAM8 is the worse, since it has the most signal at higher
frequencies.
> >
> >
> >
> >I only plotted the PSD up to 0.4*SymbolRate, because the analog
> >filters
>
> >will typically have >3dB attenuation at 0.5*Symbol rate and the PSD
> >is mostly dependent on the analog filters. PAM12 and PAM8 will both
> >have similar analog filters.
> >
> >For those interested in the details I included the matlab code. For a
> >fixed tx power the PSD level (dBm/Hz) will drop as -10*log10(BW) when
> >we increase the bandwidth, BW. But as we increase the BW, the EMI
> >increases as 20*log10(BW). Clearly the increase in EMI in PAM8 is
> >twice
>
> >as bad as the PSD level drop.
> >
> >Thus PAM12 has 10*log10(1000)=0.8dB more signal at low frequencies,
> >but
> >PAM8 has 1.6dB more EMI at high frequencies. Therefore PAM8 has 0.8dB
> >more EMI
> >
> >Jose
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >-----Original Message-----
> >From: stds-802-3-10gbt@IEEE.ORG [ <mailto:stds-802-3-10gbt@IEEE.ORG>
> >mailto:stds-802-3-10gbt@IEEE.ORG] On Behalf Of sailesh rao
> >Sent: Tuesday, July 20, 2004 6:55 PM
> >To: STDS-802-3-10GBT@listserv.ieee.org
> >Subject: [10GBT] Request for Cat6 Emissions Characteristics
> >
> >Hi All,
> >
> >At the request of a task force member, I computed the transmit PSD
> >for PAM8,
> >PAM12 and 1000BASE-T, and discovered that I added the contribution of
> >Jose's 0.4dB incorrectly in my Total EMI Penalty calculations in the
> >updated table.
> >Actually, in the passband, the transmit PSD for PAM8 after THP is
> >1.6dB
>
> >lower than the transmit PSD for PAM12 after THP, and not 0.8dB lower
> >as
>
> >I had reported earlier.
> >
> >However, rather than simply adding another 0.8dB to the PAM12 EMI
> >penalty, I would like to propose that we compute the estimated
> >emissions characteristics of the PAM8/PAM12 transmit PSDs, for
> >different transmit filtering choices, over typical Cat6 cabling and
> >assess the difference in peaks to estimate the true emissions penalty
> >for one PAM approach over the other. I know Scott Powell had
> >published a PDF version of measured 4-connector Cat6 emissions
> >characteristics for a flat transmit PSD (powell_1_0303.pdf), but do
> >cabling experts agree with Scott's measurements and can the task
> >force use that data to
>
> >assess the emissions characteristics of PAM8 vs. PAM12? If so, I
> >would like to request Scott to publish a file version of his
> >measurements on the task force web site so that we can all use it to
> >do fair comparisons. If not, are there other typical Cat6 cabling
> >emissions measurements that we can use to do the emissions
comparisons?
> >
> >Any input from the cabling experts on the reflector would be greatly
> >appreciated.
> >
> >Regards,
> >Sailesh Rao.
> >srao@phyten.com
> >
> >_________________________________________________________________
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> >
> >
> >
> ><< PSDPAM12andPAM8.m >>
>
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