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Re: [10GBT] [SPAM] [10GBT] symbol rate

You state:
2-The complete list of PAM5 advantages are:
a-Lower SNR
b-More tolerant to AFE nonlinearity
c-Significantly lower power
I do agree with (a) and with (b) though, to avoid confusion I would state (a) as Lower SNR required.
Both (a) and (b) will reduce AFE power consumption requirements so I agree with (c) also. It is good that we agree on this at a qualitative level.
The higher baud rate does however do the following:
(d) Increase equalizer and canceller lengths
(e) Increase the required clock rate at which the above run
Because of (d) and (e) the digital power consumption goes up - to a first order as the square of the symbol rate - so going from 800Msym/sec to 1.2Gsym/sec will, to a first order, increase digital power by a factor of 2.25. Again this is a qualitative argument.
As for the capacity calculations with SolarFlare's program, I will leave it to people from SolarFlare to respond.
To estimate system performance, you need to calculate the SNR available at the receiver and compare this to the SNR required. For capacity calculations, any transmitted power making it to the receiver counts as signal. For system operation, part of the signal power making it to the receiver, if not equalized, will add to the noise rather than to the signal. The way to estimate actual received SNR is to adapt a DFE with a reasonable number of taps and see what this turns out to be.
I can't recall whether someone put up Matlab code to do this SNR calculation up on the reflector. If it is, can someone point us to it?
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From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On Behalf Of Joseph Babanezhad
Sent: 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
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