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Hi
Sailesh,
As was discussed last week, the bottom line performance goal is 1e-12 BER which
is determined most directly by the SNR at the decision device ("slicer SNR") by
the familiar BER vs SNR curves the task force has been using so far.
I'd much rather see results presented in terms of slicer SNR than the
more obscure "input-referred RMS noise power". The margin is then simply
the dB difference between the "required SNR" and the slicer SNR.
Perhaps others could voice their preference.
As was also discussed, the "required SNR" for LDPC codes must be determined
by simulation. Error floor and BER slope change issues inherent to
many LDPC codes cannot be predicted and simulations must be performed to
demonstrate that 1e-12 BER performance is possible from any given code.
Extrapolations from 1e-9 or 1e-10 (or even 1e-11) are not always a reliable
predictor of required SNR for 1e-12 BER. We have not yet
seen results presented that establish the required SNR for the PAM8 case with
the proposed LDPC (2048,1723) code as we have for the PAM12
case.
Lastly, we didn't have time to discuss this in detail last week but there is
some concern about the applicability of the so called "Crane" noise immunity
test for these PHYs. Another bottom line performance goal is
for the *PHY + connecting hardware* to pass legally required noise immunity
tests. The noise immunity test consists of modulated sinusoidal fields
applied to an actual operating PHY in a system. This PHY will still have
all other noise sources and will have it's cancellers and equalizers in normal
operating mode. As I understand it, the "Crane test" puts the PHY in the
unrealistic condition of 1) no other external noise sources and 2) equalizers
frozen, not adapting. The Crane test makes the further assumption that the
same coding gain predicted for white Gaussian noise will be valid for sinusoidal
noise - I don't believe I've seen presentations or literature which backs this
assumption up. I don't think we have had enough discussion on the Crane
test's advantages/disadvantages, options, and relationship to reality to simply
adopt it and use the results to base our PHY architecture decision
on.
Regards,
- Scott
Dr. Scott Powell
Senior Manager, Ethernet PHYs
Broadcom Corp.
(949)926-5105
spowell@broadcom.com
Sailesh,
Please, define
default cancellation parameters and necessary parameters to create transmit
PSDs for both PAM8 and 12.
Hiroshi
KeyEye
From:
stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On Behalf Of Sailesh Rao
Sent: Friday, July 16, 2004 9:01
PM
To:
STDS-802-3-10GBT@listserv.ieee.org
Subject: [10GBT] Proposed PAM8 vs. PAM12
resolution process
All,
I would like to propose the
following process for resolving the robustness of PAM8 vs. PAM12 towards
external noise.
1. Compute the Optimum DFE SNR
Margin for PAM8 and PAM12 using solarsep_varlen7a.m for Models 1 and 3 using
default cancellation parameters and -150dBm/Hz background
noise.
2. Compute the input-referred RMS
noise power at the slicer by integrating the residual noise in the Optimum DFE
solution. I volunteer to add this code to solarsep_varlen7a.m unless someone
else wants to do so.
3. Compute the input-referred
external noise power that can be tolerated for a BER of 1E-12 for both systems
using the results from (1) and (2) above. I volunteer to add this code to
solarsep_varlen7a.m unless someone else wants to do
so.
Regards,
Sailesh
Rao.
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