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Re: [10GBT] symbol rate

The MATLAB code solarsep_varlen7a provided by SolarFlare seems to be working only for BW (parameter 'bwmhz' in the code) of 650 MHz.
I try to change it to 450 or 500, and it gives me an error. I'm not sure if we r using the correct version. Can SolarFlare please clarify, or may be it
is written specifically only for BW of 650 MHz? Being able to change this parameter will enable us to do relative comparison, and
i guess, the program wud have universal appeal. Please kindly provide ur feedback.
----- Original Message -----
Sent: Wednesday, May 19, 2004 9:07 AM
Subject: Re: [10GBT] [SPAM] [10GBT] symbol rate

Joseph –

The main value of the program you used is that it gets beyond capacity limitations.  The constellation sizes noted in the printout ( PAM-4) are for uncoded.  PAM-5 at 1250 Mbaud is equivalent to coded PAM-4.  In order to get the margin for the PAM-5 system, you can take the PAM4 DFESNR (which is the Optimal DFE SNR for 1.25 Gbaud PAM, regardless of the number of levels), and subtract from it the SNR that your coded system requires.

Equivalently the PAM_2p5 DFESNR is the optimal DFE SNR for a 1 Gbaud system (regardless of the levels), and the PAM8 DFESNR is for an 833.333 Mbaud system (3 bits/baud/pair at 10 Gbps) regardless of the number of levels.   For coded margins, these SNRs can be compared to the SNRs listed for the coded systems, properly adjusted for shaping gain or precoding loss.


For reference, you mentioned a 1.56 Gbaud PAM-4 system, which I presume has coding overhead, it would be equivalently (10Gb/sec / 4 pairs / 1.56 Gbaud = 1.60 bits / baud).



I hope this helps.


The point of all this is that it is well-known that increasing the bandwidth of a DFE, DFSE, or TH Precoded system does NOT always give you the benefit of the increase in the channel capacity by including more bandwidth.  You CAN signal too fast for the channel.  The point of diminishing return is usually where SNR(f) (SNR at a given frequency f) approaches zero (crossover of signal and noise) for all frequencies > f_o.  For PAM systems, f_o will be the nyquist rate, half the baud rate.  Signalling beyond this rate generally adds less to the SNR in marginal capacity than it loses due to the additional noise and shorter baud interval.  See slide 25 (1st backup) in my presentation at the last meeting for the basic math, or go directly to the reference: J. Salz, “Optimum mean-square decision feedback equalization”, Bell System technical Journal, pp. 1341-1373, Oct. 1973.



Joseph, on another topic,I also see that you have had to increase the echo, next and fext cancellation numbers significantly over the default values.  This seems to fly in the face of your claimed improved nonlinearity tolerance.  While the received equalized signal in the absence of interference will be more tolerant to nonlinearity, nonlinearities following the point where the reference for next/fext and echo cancellation are taken will will show up as residual echo, next, and FEXT, and hence a good proxy for the linearity requirements is the maximum degree of cancellation required.  The signal that has to be cancelled (echo, next or fext) will have a near Gaussian PAR in reality, so the linearity of the canceller or cancellation signal is largely independent of the number of levels used in the line code.  As such, you seem to have required some 50 dB of linearity for FEXT cancellation alone, (was 30 dB), and upped the echo cancellation to 65 dB.  Did you really require those increases?



-----Original Message-----
From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On Behalf Of Joseph Babanezhad
Wednesday, May 19, 2004 3:25 AM
Subject: Re: [10GBT] [SPAM] [10GBT] symbol rate




In May of 1998 at the CICC conference while waiting to present my paper

I was listening to Mehdi Hatamian of Broadcom, one of the movers & shakers

of IEEE 1000BASE-T standard, give his tutorial presentation on 802.3ab standard

draft. There was one thing that he kept repeating it over and over ... and over again;


"Remember the most important things for Ethernet are power, power and power"


If this was relevant to 1000BASE-T it definitely is more relative to 10GBASE-T.

With this in mind let me address your comments:


1-Please do not confuse PAM4 with PAM5


PAM4 baud-rate=1.56 GB/s  Nyquist-frequency=780 MHz

PAM5 baud-rate=1.25 GB/s  Nyquist-frequency=625 MHz


2-The complete list of PAM5 advantages are:


a-Lower SNR

b-More tolerant to AFE nonlinearity

c-Significantly lower power


3-As far as channel's higher IL & ANEXT at frequencies beyond 500 MHz are

concerned the following are the capacity simulation results using SolarFlare's

provided program from the web-site:


Launch Power : 7 dBm (2Vpp PAM5)


nextcanc=50; echocanc=65; fextcanc=50;


(1) for model # 1


17.38 Gbps


(2) for model #2



18.40 Gbps


(3) for model #3



17 Gbps






Joseph N. Babanezhad

Plato Labs.



----- Original Message -----

Sent: Tuesday, May 18, 2004 9:14 PM

Subject: [SPAM] [10GBT] symbol rate


Looking through some of the prior presentations proposing 4PAM and 5PAM I see that the significant benefits claimed for 5PAM or 4PAM are

a) Lower  SNR requirement.

b) Lower linearity requirement


Going from 5PAM to 10PAM raises the SNR required for the same BER by 6dB.


The increase in SNR required is indeed painful, however the presentations proposing the lower PAM do not take into account the fact that

a) The higher symbol rate will result in higher net attenuation since the transmit spectrum extends to higher frequencies where the attenuation is higher

b) The alien cross talk is higher at higher frequencies.

Both a and b result in the available SNR being lower than what you get at symbol rates below 1Gsym/sec for the Channel models #1 and #3.

For short cable lengths or lower attenuations, this effect is less severe.


Bottom line is that beyond about 1Gsym/sec, the theoretically achievable system margins drop off sharply.


The higher PAM  (8, 10, 12 etc) will require higher SNR and this implies higher linearity requirements at the transmitter, lower noise in the receiver than if you targeted a shorter distance using 5PAM however I don't think this is a choice we have given our distance objectives.


Please note that this is my personal opinion and not a directive as editor.


I leave this as a qualitative argument because quantitative arguments have been made earlier but don't seem to have been accepted by some.  I hope this helps.




Sanjay Kasturia

cell (650) 704-7686

office (408) 653-2235

fax (408) 844-8187


Teranetics Inc.

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Santa Clara, CA 95054