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Re: [10GMMF] TP3 3-impulse test proposal

Ben thanks for the clear summary and thanks to all for clearly stated questions.

[9] When one considers the offset launch at 17-23um, the resulting mode power distribution looks more Gaussian than a "3 impulse" example. There are always more pulses.  The fibers which give a relatively low offset BW and which represent a test of EDC have an "alpha error" in that region, so that there is a sequence of pulses at roughly equal intervals with a Gaussian-like envelope.
        Since EDC seems to be more stressed by Gaussian transfer functions why are we using a 3-impulse model rather than a 5-impulse model (for example)?  Is the 3-impulse worst case or is it primarily easy to implement (answer [4])?

-----Original Message-----
From: Ben Willcocks [mailto:ben.willcocks@PHYWORKS-IC.COM]
Sent: Tuesday, September 21, 2004 8:32 AM
Subject: Re: [10GMMF] TP3 3-impulse test proposal

Thank you for the various comments and questions relating to our TP3 3-impulse test proposal.  I will endeavour to address them all here:

Paul Kolesar asked:

1] > What is the purpose of this dynamic test?

Our aim was to produce a test which would verify that the equaliser can track a changing channel response, as suggested by Lew Aronson.

2] > Does its purpose explain why the pre and post cursors never exceed the amplitude of the central pulse?

Our intention was to provide stress commensurate with the Cambridge fibres throughout the test.

3] > Has anyone analyzed other test cases with more or less than three impulses?

Yes, Petre Popescu has done some excellent work on this topic recently.

4] > What has led to the choice of three?

Ease of implementation.  We simply took Lew Aronson's 3-impulse proposal, and we believe we have verified that it can produce an appropriate level of stress, measured with the PIE metrics.

Sudeep Bhoja commented:

5] > I would suggest that we use Tx rise times consistent with TP2 specifications for computing the link dispersion penalty from the fiber models. Hence, using 30ps for the Tx rise time under estimates the dispersion penalty. For reference, the -LR rise time is 47.1ps for the 20-80% rise time of the Tx.

We chose the 30ps rise time filter for consistency with Petre Popescu's work.  As we are making a comparison between PIE metrics for the 3-impulse test and PIE metrics for the Cambridge fibers (using the same filters in both cases), the exact rise time of the tx filter has very little effect on the result.

Changing from a 30ps rise time to a 47.1ps rise time, the increases in the PIEs for the 80th centile Cambridge fiber at 220m are matched (to within 0.1dBo) by similar increases in the PIEs for the 3-impulse tests.

Tom Lindsay asked:

6] > Please clarify for me - is this work focused only on a dynamic test, or does it also suggest a static test? Would the dynamic test be separate or combined with a static stress test?

Lew Aronson has proposed separating the static and dynamic tests, and we were focusing on the dynamic test.  It may be advantageous to define something simpler to implement for the static test, for example a fixed low-pass filter.

Lew Aronson commented:

7] > We should do this calculation (and all similar calculations) for 300m as well as 220m.

I will add 300m figures to the slides.

8] > I am concerned about deriving the details of the impulse response parameters solely from PIE metrics... I would suggest that, at least in the case of the dT choice, that the fiber models and Petre's work be used to determine the approximate choice, and that we live with a larger difference in PIE-L and PIE-D that results.

This is a good point.  However, we felt that it would be desirable to make the dynamic test straightforward to implement, with the idea that one could rely on the static test to verify that equaliser implementations have adequate time span.