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Re: Equalization




IGair:

I mean the frequency responce affected by DMD, the optical path will change, 
and the DMD pattern will change to affect the resultant frequency response.


Regards, 
Ed Chang 
NetWorth Technologies, In.

e
<< 
 Ed,
 
 I don't think so.  Why should it?
 
 Gair
 
 
 Edward Chang wrote:
 > 
 > Larry:
 > 
 > When move the fiber, the DMD pattern changes
 > 
 > Regards,
 > 
 > Edward S. Chang
 > NetWorth Technologies, Inc.
 > EChang@NetWorthtech.com
 > Tel: (610)292-2870
 > Fax: (610)292-2872
 > 
 > -----Original Message-----
 > From: Larry Rennie [mailto:Larry.Rennie@nsc.com]
 > Sent: Friday, July 21, 2000 6:02 PM
 > To: Gair Brown; Edward Chang
 > Cc: HSSG
 > Subject: 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@nswc.navy.mil>
 > To: Edward Chang <edward.chang@NetWorthTech.com>
 > Cc: HSSG <stds-802-3-hssg@ieee.org>
 > 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@NetWorthtech.com
 > > > Tel: (610)292-2870
 > > > Fax: (610)292-2872
 > > >
 > > > -----Original Message-----
 > > > From: Gair Brown [mailto:gdbrown@nswc.navy.mil]
 > > > 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@NetWorthtech.com
 > > > > Tel: (610)292-2870
 > > > > Fax: (610)292-2872
 > > > >
 > > > > -----Original Message-----
 > > > > From: owner-stds-802-3-hssg@ieee.org
 > > > > [mailto:owner-stds-802-3-hssg@ieee.org]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@worldwidepackets.com]
 > > > > > Sent: Thursday, July 20, 2000 4:07 PM
 > > > > > To: 'vipul.bhatt@finisar.com'; 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@finisar.com]
 > > > > > >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@nswc.navy.mil
 > > > 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@nswc.navy.mil
 > > 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@nswc.navy.mil
 Code B35                                               PH:  540-653-1579
 17320 Dahlgren Road                                    FAX: 540-653-8673
 Building 1500 Room 110A
 Dahlgren, VA 22448-5100
 
 
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