Re: Equalization
Rich:
Thanks for appreciate and share the difficult discussion of MM fiber
equalization we are discussing.
Furthermore, I do agree that you guys have led a lot of discussion of the
equalization issue before fro multilevel proposal; as a result, the
equalization techniques are more familiar for all of us to deal this time.
Regarding to the intergap comment, I did not elaborate clearly; as a result,
it is misinterpreted by readers. I did not mean that the equalization will
include the intergap design at all. That is my fault, sorry about that.
What I tried to mention is that the DMD related frequency response is random,
irregular and varies depending on the beam path inside the fiber. It is
timing dependent, but not a static parameter. Therefore, the equalizer has
to have the ability to modify, and correct the equalization accordingly in a
timely response manner. Therefore, the question is what is the rate of
correction? It will need to collect a lot of actual system dynamic
parameters to determine how to define the rate of correction to assure BER of
10^-12.
Further more, not to forget to include the dynamics of the intergap
parameters in the study, and there are some new parameters. Assume someone
will use intergap-length time to modify/correct the equalization, then the
rate of correction will be affected by the length of the intergap and
activities during that time. There are many timing-dependent parameters in a
system to influnce equlizer design. We need time to study all these
parameters, but not to rush in to make decision immaturely.
I should not overly simplified all these statements in one sentence to lead a
misinterpretation.
Regards,
Ed Chang
NetWorth Technologies, Inc.
I agree with many of the points you are making with respect to the
difficulty of characterizing the frequency response of a
laser/multi-mode fiber optical link in order to equalize for the effects
of multi-mode dispersion.
However, I don't believe that such characterization is impossible, it's
just very difficult. As a level set and in light of the objective of
this equalization thread: to extend multimode cable plant distances
using laser sources at a given data rate, I would personally instead
chose to go to multilevel signaling first. It's likely to be easier,
lower power, applicable to a broader base of fibers, etc. Please don't
misunderstand me, I'm not trying to bring back multi-level signaling at
the moment. I'm just commenting about the difficulty of this
equalization effort. As Oscar Agazzi and I have presented and explained
to the Task Force, equalization and multi-mode signaling are orthogonal
and both can be employed separately or in combination to enable extended
link distances.
The real purpose of this note is to properly frame the level of
difficulty of this equalization effort. You stated that the design of
the equalizer would include: "intergap inserting bits, error check,
speed correction". This is not true and should not be used as an
argument against investigating equalization techniques. These other
required 10 GbE link functions are completely orthogonal to equalization
have associated with them accepted proposals and are based on proven
technology. Let's not obfuscate the equalization task ahead of us if we
seriously plan to invest any effort in it.
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