Re: Missing MAS in Maui
a lot of alliteration from assertive article authors...
At 08:24 PM 20-12-99 -0600, Patrick Gilliland wrote:
>Rich,
>[...]
> >You're confusing signaling rate with bandwidth. The fastest signaling at the
> >transmitter for PAM5x4, that being an NRZ multi-level code, is 2.5 GHz. In my
> >MAS update presentation in Kauai, I specified the following Tx and Rx
> >bandwidths, which correspond to your numbers:
> >
>-------------------------------------------------------
>I apologize for the confusion on my part; when one uses
>the "GHz" symbol I understand it to mean frequency.
>-------------------------------------------------------
rich's comment is accurate -- a 5-Pam 5Gbaud line rate corresponds to a 2.5GHz
fundamental line frequency (here i ignore rise- and fall-time to illustrate a point).
the terms are not interchangeable yet people are not always careful with that
distinct quality.
> >I agree. This is the well known 1300 vs. 850 nm tradeoff, but has nothing to do
> >with MAS.
>-------------------------------------------------
> From my point of view it has a lot to do with MAS.
>MAS is the reason behind any SNR degradation at the
>transmitter. With 1300nm, there is room below the
>laser safety limit to increase transmit power and
>therefore offset the SNR degradation occasioned by
>MAS.
>---------------------------------------------------
you two seem to be talking past each other.
for the same average power level no one can dispute that multi-level
modulation entails added power penalty for x-PAM, where 'x' is any
integer larger than 2. yes, one can easily argue that LW diodes offer
an advantage over SW diodes in power budget simply because an eye
safety limit for LW is much higher than for SW. but this viewpoint is
narrow in that it does not allow for 'effective' SNR improvement through
use of schemes like forward error correction (FEC).
now, right away someone will complain about higher cost of more
complex silicon. but then i argue that side emitters are already very
expensive, and in the long run all of us really want to push cost out
of optics and into silicon anyway.
FEC details have not been described, but with it you can separate
design issues for SNR and MAS.
------------------------------------------------------
>[...]
>I would not lump multilevel in with WDM because WDM is a
>mainstream technology, widely deployed, and well character-
>ized. Multilevel optical signalling has not been deployed
>anywhere to my knowledge.
>-------------------------
but MAS can be applied whether or not there is also a cost-effective
solution in (D)WDM, thus affording the best of both worlds.