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Re: [10GBT] Proposed PAM8 vs. PAM12 resolution process

Title: Message
Hi Scott,
On the subject of the Crane test, it is just a simple way of evaluating system robustness against noise. There is no reason why it cannot be evaluated with worst case impairments ON, as well as OFF. But I believe the cancellers/equalizers do need to be frozen, because the intent is to capture the effect on the system of a transient noise event, that is not long enough to allow the system to adapt to it. I agree with you that the coding gain validity is in question, but since we are (fortunately) comparing very similar systems (both PAM, and both using LDPC), I'm assuming that this will affect both systems equally.
-----Original Message-----
From: []On Behalf Of Scott Powell
Sent: Sunday, July 18, 2004 2:37 AM
Subject: Re: [10GBT] Proposed PAM8 vs. PAM12 resolution process

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.
  - Scott
Dr. Scott Powell
Senior Manager, Ethernet PHYs
Broadcom Corp.
-----Original Message-----
From: [] On Behalf Of hiroshi takatori
Sent: Friday, July 16, 2004 11:09 PM
Subject: Re: [10GBT] Proposed PAM8 vs. PAM12 resolution process


Please, define default cancellation parameters and necessary parameters to create transmit PSDs for both PAM8 and 12.



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
Subject: [10GBT] Proposed PAM8 vs. PAM12 resolution process




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.



Sailesh Rao.