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Re: PAM-5 at 1.25 Gbaud


I wholeheartedly support your claims. I did not go to York: it should
teach me not to miss any meetings.

I attach a new pdf spreadsheet for MMF with the corrections. The
first one, regarding the "swing" of a PAM5 signal was easy to make:
the new entries under"electrical signal power @ Rx" show now the
same total swing for both PAM-5 and PAM-2 signals under similar
conditions (for instance, using 4-WDM).

I included the PAM-5 penalty and ISI loss under the same row
because the net effect of both is similar: they reduce the distance
between the levels.

I also corrected the penalty due to the use of PAM-5 to reflect your
4.1 dB value (optical). In this area I still have to do some learning.

The third grouping of four entries concentrate the inputs needed to
calculate the final quantity of interest, the relative electrical SNR.


Do you agree on this issue of PAM-5 penalty ? A tutorial
explanation, if possible, would be greatly appreciated.

Many thanks for your comments.


Jaime E. Kardontchik
Micro Linear
San Jose, CA 95131

Rich Taborek wrote:

> Jaime,
> My basic disagreement with your spreadsheet is that you seem to be simply
> summing optical intensity penalties, with little regard for how the penalties
> interact. In addition, some of these penalties are not quite accurate.
> In general, the factor limiting the distance of a gigabit MMF link is ISI, not
> optical intensity. I believe that the HP/Agilent model developed by Del Hanson,
> et. al. does a good job of assessing the coupling between different link
> penalties. It does not do so in a straight additive fashion as your spreadsheet
> does.
> For example, for PAM5 loss, you note a penalty of 6 db optical. My understanding
> is that this penalty is an SNR penalty whose value is more correctly 4.1 db
> optical. The "swing" of a PAM5 signal at the receiver is of approximately the
> same amplitude from the lowest PAM5 level to the highest as it is for a PAM2
> (binary signaling) 0 -> 1 transition. It is incorrect to simply subtract even
> 4.1 db from the link budget due to PAM5 loss, especially in light of coding gain
> which can significantly increase effective SNR.
> In York (September '99), Del Hanson proposed modifications to the GbE link model
> to extend the model to be used for 10 GbE PMD development. I also presented some
> issue modeling issues. I believe that it's in the best interest of the HSSG to
> use a common, well understood and proven link model for 10 GbE PMD development.
> I suggest that you obtain a copy of Del's model and use or modify it to get a
> better apples to apples comparison of the various PMD proposals including
> yours.
> Best Regards,
> Rich
> --
> Jaime Kardontchik wrote:
> >
> > Hello 10Giga'ers,
> >
> > I have received some private emails saying that
> > I might be underestimating the performance of
> > my own proposal ...
> >
> > May be that I am to blame for this in the way
> > I constructed the spreadsheet for the installed
> > MMF.
> >
> > In the entry corresponding to the "electrical
> > signal power @ Rx", the PAM-5 at 1.25 Gbaud
> > proposal would appear to have much less signal
> > power compared to the other on-off n-WDM
> > proposals (n=4,5)
> >
> > In practice, the input power at the Rx of my proposal
> > does not differ from the input power of the other
> > on-off n-WDM proposals. What happens is that,
> > for the purposes of calculating the SNR, what is
> > important is the *difference* between adjacent levels.
> > For a  5-level approach this difference is much
> > smaller. And it is this difference between adjacent
> > levels that appears under the entry "electrical
> > signal power @ Rx".
> >
> > Of course, this smaller "differential power"
> > between levels is  compensated by the smaller
> > noise power due to use of a smaller receiver
> > bandwidth.
> >
> > Jaime
> >
> > Jaime E. Kardontchik
> > Micro Linear
> > San Jose, CA 95131
> > email: kardontchik.jaime@xxxxxxxxxxx
> -------------------------------------------------------------
> Richard Taborek Sr.         Tel: 408-845-6102 or 408-370-9233
> Chief Technology Officer                   Cell: 408-832-3957
> nSerial Corporation                         Fax: 408-845-6114
> 2500-5 Augustine Dr.            Email: rtaborek@xxxxxxxxxxxxx
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