|
Sanjay,
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
solarsep_varlen7a(-10.5,650,4,55,6,1,6,2)
18.40 Gbps
(3) for model #3
solarsep_varlen7a(4.5,650,4,100,6,1,6,2)
17
Gbps
Regards,
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.
Regards,
Sanjay Kasturia
cell (650)
704-7686
office (408)
653-2235
fax (408)
844-8187
Teranetics Inc.
2953 Bunker Hill Lane, Suite
204
Santa Clara, CA
95054
|