Re: Equalization
I am also a bit confused regarding the time variance of the fiber
characteristics. What is their about the fiber that makes the
chracteristics time variant? Vipul, you too had an e-mail that said the
fiber was time-variant.
Regards,
Larry Rennie
----- Original Message -----
From: Gair Brown <gdbrown@xxxxxxxxxxxxx>
To: Edward Chang <edward.chang@xxxxxxxxxxxxxxxx>
Cc: HSSG <stds-802-3-hssg@xxxxxxxx>
Sent: Friday, July 21, 2000 1:56 PM
Subject: Re: Equalization
>
> Ed,
>
> You need to talk to some of the participants of the FO-2.2.1 round
> robins. I suspect that some of the participants do have data that
> contains phase information.
>
> On a different note. I believe that the fiber response is relatively
> invariant with respect to time. There is variation between different
> fibers, but for fibers selected using the RML requirements the variation
> should be manageable.
>
> Gair
>
>
> Edward Chang wrote:
> >
> > Gare:
> >
> > The characterization done by Fo2.2.1 is are from optical property point
of
> > view, which is very important of understanding the static optical
> > parameters.
> >
> > The equalization need different parameters, time domain frequency
response
> > with the information of amplitude, phase versus frequency, and the
dynamic
> > nature of the response and error correction rate relative to fiber
motions.
> > Furthermore, one has to define, how far we intend to deal with the DMD
> > caused BW deficiency based on the installed MM fiber, then we can setup
the
> > target specifications for equalization circuit to be designed.
> >
> > In all, the timing related parameters, and time domain frequency
responses
> > will be established.
> >
> > If we have time, eventually we will get some meaningful result. This is
> > reason, I have proposed 5 PMDs to allow each PMD opportunity to be
improved
> > later.
> >
> > Regards,
> >
> > Edward S. Chang
> > NetWorth Technologies, Inc.
> > EChang@xxxxxxxxxxxxxxxx
> > Tel: (610)292-2870
> > Fax: (610)292-2872
> >
> > -----Original Message-----
> > From: Gair Brown [mailto:gdbrown@xxxxxxxxxxxxx]
> > Sent: Friday, July 21, 2000 2:15 PM
> > To: Edward Chang
> > Cc: HSSG
> > Subject: Re: Equalization
> >
> > Ed,
> >
> > The characterization has already been done by FO-2.2. I believe Mike
> > Hackert's working group has a ton of data on the frequency response of
> > RML compliant fibers.
> >
> > Gair
> >
> > Edward Chang wrote:
> > >
> > > Rohit:
> > >
> > > It is interesting. You ,may like to share your results with us?
> > >
> > > However, fiber dispersion and DMD is not exactly the same thing.
> > > The linear dispersion proportional to cable length is straight
forward,
> > the
> > > dispersion related to the non-linear DMD is different. We need
> > > characterization.
> > >
> > > Regards,
> > >
> > > Edward S. Chang
> > > NetWorth Technologies, Inc.
> > > EChang@xxxxxxxxxxxxxxxx
> > > Tel: (610)292-2870
> > > Fax: (610)292-2872
> > >
> > > -----Original Message-----
> > > From: owner-stds-802-3-hssg@xxxxxxxx
> > > [mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Rohit Sharma
> > > Sent: Thursday, July 20, 2000 9:21 PM
> > > To: HSSG
> > > Subject: RE: Equalization
> > >
> > > i believe DMD can be (has been) modelled as a Rayleigh multipath
fading
> > > channel and fast Decision Feedback Equalization (DFE) techniques with
RLS
> > > (Recursive Least Squares) or LMS (least mean squares) algorithms
applied
> > for
> > > rapid convergence with a short training sequence (# of bits roughly
equal
> > to
> > > the # of taps). J. Winters and cohorts in IEEE Transaction (1990 -
will
> > dig
> > > out exact ref. tomorrow) and Stanford ISL with John Cioffi did a bunch
of
> > > work in this area in 1991-95 timeframe.
> > >
> > > part of my grad studies demonstrated an 11 (goes to 11!) tap adaptive
> > > optoelectronic filter to equalize dispersion in mmf for 1 and 2.5 Gbps
> > IMDD
> > > signals. Similar results were shown by other researdch groups using
> > > electrical equalization with bipolar taps and DFE structures. some
basic
> > > simulation results are available (and were published in Optics
Letters)
> > and
> > > if anyone is interested, send me email and that will prompt me to dig
> > > through any relevant results i have...
> > >
> > > -rohit
> > >
> > > Rohit Sharma
> > > ONI Systems.
> > >
> > > > -----Original Message-----
> > > > From: Jonathan Thatcher
> > > > [mailto:Jonathan.Thatcher@xxxxxxxxxxxxxxxxxxxx]
> > > > Sent: Thursday, July 20, 2000 4:07 PM
> > > > To: 'vipul.bhatt@xxxxxxxxxxx'; HSSG
> > > > Subject: RE: Equalization
> > > >
> > > >
> > > >
> > > > Vipul,
> > > >
> > > > You have really caught my attention on this one. What exactly is a "
> > > > time-variant impulse?"
> > > >
> > > > jonathan
> > > >
> > > > >-----Original Message-----
> > > > >From: Vipul Bhatt [mailto:vipul.bhatt@xxxxxxxxxxx]
> > > > >Sent: Thursday, July 20, 2000 1:46 PM
> > > > >To: HSSG
> > > > >Subject: RE: Equalization
> > > > >
> > > > >
> > > > >
> > > > >Rich,
> > > > >
> > > > >I was skeptical, like you, about the ability of equalization to
> > > > >overcome DMD. I still am. But what made me more open minded is my
> > > > >willingness to examine two key propositions: DMD behavior can be
> > > > >approximated as that of a fading multipath channel. And
equalization
> > > > >can overcome the effect of a fading multipath channel.
> > > > >
> > > > >Why fading multipath? Consider this. A multimode fiber with DMD is
> > > > >seen by an optical signal as a channel that propagates various
> > > > >portions of its energy (modes) through a refractive index profile
> > > > >that is sharply different (at places) than intended. The
propagation
> > > > >velocity of a mode depends on refractive index. Over distance, on
> > > > >average, some modes will have a cumulative average of a low (lower
> > > > >than intended) refractive index path, thereby abnormally decreasing
> > > > >their path delay, while others may not. In some bad cases, a bit
> > > > >arriving at the receiver is almost split in two or three replicas.
> > > > >And the amplitude of each replica is changing dynamically. Guess
> > > > >what, that is not far from the behavior of a fading multipath
> > > > >channel. Equalizers that deal with this phenomenon are used in TV
> > > > >de-ghosting circuits and digital radio.
> > > > >
> > > > >To an equalization expert, DMD may not look so challenging - it's
> > > > >just another channel with randomly time-variant impulse
> > > > >response...:-)
> > > > >
> > > > >But then, we both are putting the cart before the horse. Let's wait
> > > > >to hear some presentations from equalization experts. Even if it
can
> > > > >be done, I will want to know whether it can be done
cost-effectively
> > > > >and on time. Our discussion should serve as a guide to them about
> > > > >what we would like to hear.
> > > > >
> > > > >Thanks,
> > > > >Vipul
> > > > >
> > > >
> >
> > --
> > Naval Surface Warfare Center
> > browngd@xxxxxxxxxxxxx
> > Code B35 PH: 540-653-1579
> > 17320 Dahlgren Road FAX: 540-653-8673
> > Building 1500 Room 110A
> > Dahlgren, VA 22448-5100
>
> --
> Naval Surface Warfare Center
> browngd@xxxxxxxxxxxxx
> Code B35 PH: 540-653-1579
> 17320 Dahlgren Road FAX: 540-653-8673
> Building 1500 Room 110A
> Dahlgren, VA 22448-5100
>
>