Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: [10GMMF] TP3 Meeting minutes, November 23rd

Lew, Martin-

Along the lines that we have been discussing in the conf calls, I'd suggest treating the link budget and compliance testing slightly differently.

Regarding link budget considerations, I believe there was a clear consensus across module, IC and component vendors within this group, several months back, on defining an "equalizer metric or bound" which was relatively implementation independent, so as not to constrain implementation choices & innovation, and to pad it with an "implementation penalty" corresponding to worst-case scenarios & finiteness aspects. We have the PIE-D metric, which may be somewhat constraining in subsuming a DFE-based architecture. This has worked out well so far. Note that a lot of the empirical data presented by at least one IC vendor during the IEEE meetings was using an unspecified equalizer but the PIE-D was always used as a reference. There may be different ways of achieving performance close to PIE-D, within a certain range, which may move away from the classical and strict x-tap FFE with z tap-spacing and y-tap FB. I do not expect it to be easy to come to a general consensus towards select!
 ing x,y,z - which may delay things.

Regarding compliance testing, as has been empirically (with h/w) shown within the IEEE meetings from Jan'04 and along the lines of Petre's Sept contribution, that an FIR filter (possibly cascaded with a LPF filter) can emulate the MMF channels closely. I'd agree with Lew's & Petre's suggestion to use an FIR filter with 4 peaks (taps) across a maximum 3 UI (TBD) with a certain PIE-D (~4.5 dB as been discussed in the last few calls) to set the reference compliance channel but allow for any implementation resulting in a waveform within a certain MSE from this reference. Some of the above numbers might need further validation.


-----Original Message-----
From: Lew Aronson [mailto:lew.aronson@FINISAR.COM]
Sent: Wednesday, December 01, 2004 10:21 AM
Subject: 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 Aronson  (
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
Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd


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 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.


-----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
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

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

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.


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
> 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,
> case.
> What we saw, but do not fully understand, is that it seemed that the
> the MSE PIE-D, the lareger the difference between PIE-D and any finite
> equalizer could be.  Some questioned my conclusions afterward, but
> 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.
> what we really need to know is the following: do fibers with PIE-D
> 4.5 and 5.5, which nominally seem to pass, actually have
> penalties (hardware and equalizer design) that keep them below the 6.5
> 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:
> Subject: Re: [10GMMF] TP3 Meeting minutes, November 23rd
> Importance: High
> John,
> It is an interesting proposal, at least theoretically. Assuming
> 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
> 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
> 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
> Sent: Dienstag, 30. November 2004 15:48
> To:
> 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:
> 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
> than Zero forcing Equalizers. Conventional adaptation algorithms such
> 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
> 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
> 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
> 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
> from -LR.
> For the purpose of the TP3 stressed tests, we only need to represent
> rise time of the test setup of Fig 68.6 in D0.2. For this purpose
> 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:
> 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
> 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:
> 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 <>
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)