Re: [10GMMF] TP3 Meeting minutes, November 23rd
I have long commented that a finite metric was important since the PIE metrics were not nearly as sensitive to long impulse responses, and we risk lumping in very long impulse responses into the compliance test.
The problem, of course, is what parameters (number of taps etc) to choose for the finite equalizer metric. If we make a somewhat aribrary choice which is less than what can practically be achieved, we can get results which are much too pessimistic.
I believe we have seen some presentations (sorry I can't recall the specific ones at present) on finite equalizer calculations, and generally, they seem to show that the extra penalty is very small as long as the number of taps in the equalizer is appropriate to the length of the impulse responses, and that the number of taps for the cases considered did not seem unrealistic.
I would suggest that if we do adopt a finite equalizer metric, it be with a relatively large number of taps, essentially on the high end of what the consensus feels is practical. This would not imply that you had to implement such a long equalizer, but would prevent us from coming to an overly pessimistic conclusion of the coverage, yet still prevent us from selecting overly long impulse response cases for the TP3 stressed sensitivity test.
It would be very helpful to start getting suggestions on what the parameters of this ideal finite equalizer would be even ahead of the decision to start using the metric.
Lew
Lew Aronson (lew.aronson@finisar.com)
Finisar Corporation
1308 Moffett Park Drive
Sunnyvale, CA 94089-1133
408-542-4215 (PH)
408-543-0083 (FAX)
-----Original Message-----
From: Lobel, Martin [mailto:martin.lobel@INTEL.COM]
Sent: Wednesday, December 01, 2004 3:18 AM
To: STDS-802-3-10GMMF@listserv.ieee.org
Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
All,
I completely agree with the statement that finite-length MMSE-DFE
calculations are indeed the way to go for an accurate analysis of the
problem. The infinite-length equalizer (PIE metric) has, however, the
strong benefit of very simple computation for fast estimation of the
challenge (penalty) of the problem.
I believe that there is no way around an analysis based on finite-length
equalizer in order to verify the link budget and Intel is working on
simulation results to share with IEEE. As a matter of fact, Intel
proposed back at the March meeting in Orlando (see
http://www.ieee802.org/3/10GMMFSG/public/mar04/lobel_1_0304.pdf) to
focus on finite equalizers in order to establish a link to equalizers
with realistic filter complexity and thereby include up front the
penalty associated with finite vs infinite equalizers.
Regards,
Martin
-----Original Message-----
From: owner-stds-802-3-10gmmf@IEEE.ORG
[mailto:owner-stds-802-3-10gmmf@IEEE.ORG] On Behalf Of Lars E. Thon
Sent: 30. november 2004 19:06
To: STDS-802-3-10GMMF@listserv.ieee.org
Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
Dear Robert, and other contributors to this thread,
I believe that using finite-length MMSE-DFE calculations is indeed
a more accurate method for closing the the link budget.
For an exposition on the topic, please read
http://grouper.ieee.org/groups/802/3/aq/public/jul04/thon_2_0704.pdf
which I presented in Portland in July 2004. Other contributors,
including Intel and recently Georgia Tech, have also touched upon this
subject, either directly or indirectly.
I agree with Sudeep that MMSE-DFE (whether "ideal" or finite length) is
a better measure of the required penalty term of the link budget than is
a ZF-DFE. The latter ignores noise, while the former attempts to
balance noise and the pattern-specific ISI.
Neither MMSE-DFE nor ZFE-MMSE is the "optimal" DFE (Minimum BER or
MBER-DFE). However, I think an analytic method for calculating the
MBER-DFE in the general case is beyond the reach of current
communication theory, let alone a practical goal for an adaptation
algorithm.
Hence, I think it is a good choice to use MMSE-DFE for performance
evaluation and budget closure. The ideal/PIE-D/infinite version is good
because of its simplicity, whereas one should also contemplate using a
finite length version for more accurate analysis.
Lars
Lingle, Jr, Robert (Robert) wrote:
> I am less knowledgeable than many on this list, but I am trying to
> understand the difference between the ideal, infinite case and the
real,
> finite case. As a step in that direction, we tried in San Antonio
> presentation to take a step in that direction by looking at ideal,
finite
> case.
>
> What we saw, but do not fully understand, is that it seemed that the
higher
> the MSE PIE-D, the lareger the difference between PIE-D and any finite
> equalizer could be. Some questioned my conclusions afterward, but
none
> refuted them conclusively.
>
> The implications are the following: suppose we set a limit that 99% of
> fibers must pass PIE-D < 5.5, and leave a 1 dB implementation penalty.
Then
> what we really need to know is the following: do fibers with PIE-D
between
> 4.5 and 5.5, which nominally seem to pass, actually have
implementation
> penalties (hardware and equalizer design) that keep them below the 6.5
dB
> limit? If my logic is flawed, please help me correct it.
>
> do we have to calculate finite equalizer cases as well?
>
> Robert Lingle, Jr
> Fiber Design and Development
> OFS R&D, Atlanta, GA
>
>
> -----Original Message-----
> From: Bottacchi.external@INFINEON.COM
> [mailto:Bottacchi.external@INFINEON.COM]
> Sent: Tuesday, November 30, 2004 10:23 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
> Importance: High
>
>
> John,
>
> It is an interesting proposal, at least theoretically. Assuming
infinite
> length FFE, I guess zero forcing solution would be possible (in
> principle). This means no residual ISI at sampling instant (not just
> minimum error modulus like MMSE). As a consequence, noise enhancement
is
> strongly expected to be the limiting factor for EDC performances. I am
> quite curious to see how much would be the optical penalty since I
> calculated some month ago the PID-L for the zero forcing (linear)
> equalizer in term of noise bandwidth enhancement( I sent a ppt copy to
> Sudeep for comparison with PIE-D/L reported metrics). Does zero
forcing
> PIE-D expected to be different from noise bandwidth enhancement due to
> full frequency compensation for a given output ISI free spectrum
> (raised-cosine for example)?
>
> Thank you for posting this issue...
>
> Best regards
>
> Stefano
>
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG] On Behalf Of Abbott, John S
Dr
> Sent: Dienstag, 30. November 2004 15:48
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
>
>
> In regard to Lew's and Sudeep's points, are there conditions where we
> should calculate the zero forcing PIE-D as well as the MSE PIE-D? At
> the San Antonio meeting there seemed to be comments supporting both.
>
> Regards,
>
> John Abbott
>
> -----Original Message-----
> From: Sudeep Bhoja [mailto:sbhoja@BIGBEARNETWORKS.COM]
> Sent: Monday, November 29, 2004 5:39 PM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
>
>
> Lew,
>
> This in response to your Comment #1 below.
>
> The PIE-D equations from bhoja_1_0704 targets an infinite length DFE
> that minimizes mean square error (MMSE). MMSE Equalizers perform
better
> than Zero forcing Equalizers. Conventional adaptation algorithms such
as
> LMS, minimize mean squared error.
>
> If we agree on an MMSE based infinite length DFE, there are
> two variables that enter into the calculation:
>
> 1) The first variable is easy and follows directly from the link
budget.
>
> sigma^2 -> This is the Electrical noise floor at the input
> of the ideal EDC and is easily derived from the link budget.
> We had previously set sigma^2 = 10^(-17-2*6)/10 since we had allocated
> 6dB of total dispersion budget.
>
> However since the connector loss was updated to 1.5dB from 2dB Page 5
in
> lawton_1_1104 allocated 6.5dB to the total dispersion budget.
>
> Hence we need to update sigma^2 = 10^(-17-2*6.5)/10 = 10^(-30/10) in
our
> PIE-D calculations.
>
>
> 2) The rise time used in deriving the fiber pulse response in
> bhoja_1_0104 was set to 47.1ps (20-80% Gaussian). This number was
chosen
> from -LR.
>
> For the purpose of the TP3 stressed tests, we only need to represent
the
> rise time of the test setup of Fig 68.6 in D0.2. For this purpose
47.1ps
> is probably an adequate rise time.
>
> Best Regards,
>
> Sudeep
>
>
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG]On Behalf Of Lew Aronson
> Sent: Monday, November 29, 2004 12:47 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
>
>
> Some comments:
>
> 1) I think it is very important that all are aligned on the PIE-D
> calculation. I would be interested in a discussion on the variables
> mentioned below, what differences exist now between different task
force
> members algorithms and the likely impact of changes of each of these
> parameters.
>
>
> Lew
>
>
>
> -----Original Message-----
> From: Michael Lawton [mailto:mike_lawton@AGILENT.COM]
> Sent: Wednesday, November 24, 2004 6:10 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: [10GMMF] TP3 Meeting minutes, November 23rd
>
>
>
> Dear TP3ers,
>
> Here are my notes from yesterdays call.
>
>
>
> Key issues which were raised:-
> PIE-D has variables associated with it (rise time, sigma^2, ZF
> vs MMSE calculation) - how do we handle that?
>
> Any comments/corrections please get back with me.
>
> Best Regards
>
> Mike
--
----
Lars E. Thon <lars@aeluros.com>
Aeluros Inc., 201 San Antonio Circle, Suite 172
Mountain View, CA 94040-1254
650-917-4113(w) 650-917-7394(f) 408-439-5914(c)