Re: Equalization

[Sudeep Bhoja <sbhoja@xxxxxxxxxx>]

David,

In case you are inclined to infer that the references are rather old
and theoretical, here are more recent references on implementation
of Equalizers at 10 Gbps.  The technology described in these references
demonstrate feasibility of Equalizers for Serial PMD solutions on MMF.

H. Bülow, "Adaptive PMD Mitigation at 10 GB/s using an Electronic SiGe
Equaliser IC", European Conference on Optical Communications (ECOC),
Nice France, September 1999, paper WeC3.4.

H. Bulow, F. Buchali, W. Baumert, R. Ballentin, T. Wehren, "PMD
mitigation at 10 Gbit/s using linear and nonlinear integrated electronic
equaliser circuits", Electronics Letters, vol.36, no.2, January 2000,
pp.163-164.

S. Kasturia,  J. H. Winters "Techniques for high-speed implementation of
nonlinear cancellation". IEEE Journal on Selected Areas in Communications,
vol.9, no.5, June 1991, pp.711-717.

There are a few more papers on Electronic Equalization in this years OFC
proceedings.

Thanks,

Sudeep Bhoja
Member of Technical Staff, High Speed Physical Layer, Lucent Technologies.
Phone: 408-952-8824
Email: sbhoja@xxxxxxxxxx
 
 
 

David Kabal wrote:

 Oscar and Vipul:Thanks for the education and clarification. I have some reading to do.... 8-)It is interesting to note that a good portion of the references given (optical ones, anyhow) are 10 years old. I am not sure what to infer from this, but it is interesting, anyhow.Cheers,Dave-----
David Kabal
Photonics Engineer, OPTera Metro Solutions, Nortel Networks
Phone: 613.270.5953  Fax: 613.591.2035
e-mail: dkabal@xxxxxxxxxxxxxxxxxx

-----Original Message-----
From: Vipul Bhatt [mailto:vipul.bhatt@xxxxxxxxxxx]
Sent: Wednesday, July 19, 2000 3:43 PM
To: stds-802-3-hssg
Subject: RE: Equalization
 

David,I am happy to share with you whatever information I have, and invite others to help. Please understand that it is difficult to select just a few references when talking about an unsolved problem.First, the terminology. By "electrical equalization", I mean that the equalizer black box has electrical input and electrical output. This is to distinguish it from optical equalization, which can be achieved with optical devices without converting an optical signal to electrical domain. Of course, electrical equalization can be used in fiber optic links, typically in the receiver front end. For simplicity, I will call it equalization. Deployment of equalization is difficult for me to discuss in a public forum, because often equalization is viewed as a means of achieving differentiation. I can tell you that major suppliers of (singlemode) optical transmission systems consider equalization as an old and trusted friend. Literature on channel modeling or equalization can be categorized into singlemode [1][2], multimode [3][4], circuits [5][6] and systems [7]. Unfortunately, DMD is a relatively recent discovery [8]. When it comes to equalizing the DMD effect[9], references are hard to find. I am hoping that some folks on this reflector will think about whether DMD behavior can be modeled as a previously known channel behavior (fading multipath?), and therefore equalized using known methods [10]. References:1. J.L.Gimlett, N.K.Cheung, Journal of Lightwave Technology, Vol. LT-4, No. 9, Sept. 1986, pp 1381-1392.2. G.P.Agrawal et al., Journal of Lightwave Technology, Vol. 6, No. 5, May 1988, pp 620-625.3. B.L.Kasper, Bell System Technical Journal, September 1982. 4. G.D.Brown, Journal of Lightwave Technology, Vol.10, No.5, May 1992, pp 672-678.5. S.Kasturia, J. Winters, IEEE Journal on Selected Areas in Communications, Vol.9, No.5, June 1991.6. M.Shakiba, International Solid State Circuits Conference, 1999, Paper WP 23.3.7. R.W.Lucky, Bell System Technical Journal, April 1965.8. L.Raddatz et al., Journal of Lightwave Technology, Vol.16, No.3, March 1998.9. Q.Xiang et al., IEEE LEOS Annual Meeting, paper TuR2, Nov.1999.10. J. Proakis, Digital Communications, McGraw Hill, 1995, ISBN 0-07-051726-6. Thanks,Vipulvipul.bhatt@xxxxxxxxxxx
(408)542-4113
=============================

-----Original Message-----
From: owner-stds-802-3-hssg@xxxxxxxx [mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of David Kabal
Sent: Tuesday, July 18, 2000 11:13 PM
To: stds-802-3-hssg
Subject: RE: Equalization
 

Vipul:

Equalization sounds very promising, and I think this might yield a consensus solution, if it proves viable, for the distance/media objectives it would satisfy.

I've recently been poking at optical folks to try electrical-type equalization on optical systems, but they seem to be making negative noises back at me.... (rate equations not simplifiable, too many parameters to simply model). Since I do not share their pessimism, I'd like to get a bit more information, and since you brought it up, I thought I'd ask you.

- Has optical equalization been tried or deployed before by a system or component vendor? (if so, can you give a reference or two for us to chase down)

- If I wanted to get a good seminal work on optical equalization (if one exists), where would I look (paper/author/journal/year).

To summarize: YES, I believe it's worth discussing and researching.

Thanks,
Dave

-----
David Kabal
Photonics Engineer, OPTera Metro Solutions, Nortel Networks
Phone: 613.270.5953  Fax: 613.591.2035
e-mail: dkabal@xxxxxxxxxxxxxxxxxx

-----Original Message-----
From: Vipul Bhatt [mailto:vipul.bhatt@xxxxxxxxxxx]
Sent: Tuesday, July 18, 2000 9:57 PM
To: stds-802-3-hssg
Subject: Equalization
 

Dear colleagues,

As we think about 10G on installed MMF, there is one issue we
haven't discussed - equalization. Perhaps thinking about it will
throw more light and provide another perspective.

In theory at least, equalization looks very promising. Even at 850
nm, it can permit a Serial PHY to operate over 100 meters on
installed MMF, or a WWDM PHY to operate over 300 meters on installed
MMF. At 1310 nm, longer distances can be achieved. (Ignoring DMD for
the moment, and using a linear system single pole approximation, a
20 dB equalization gain will make a 100 meter segment of installed
MMF look like a 16 GHz channel at 850 nm.) It can be cost
effective - a single BiCMOS chip with DSP on CMOS, and receiver
preamplifier in SiGe. It may even eliminate the mode conditioning
patch cord.

In reality, there are a couple of challenges, applicable to both 850
nm and 1310 nm cases.

1. DMD: Can equalization overcome DMD? Some have suggested that DMD
can be modeled as a multipath effect, something that the folks in
wireless industry know how to deal with. When viewed in terms of a
transversal filter, the multipath problem boils down to having
enough taps and setting their coefficients. And if we can undo the
DMD effect with an IC, we can eliminate the mode conditioning patch
cord.

2. Initialization: After power on, are a few milliseconds of
randomized A/K/R enough to initialize the equalizer? Can we assume
that equalizer will not need to be re-calibrated after that? We
don't want the tail wagging the dog - equalization should not
require complex Auto Negotiation.

Though new to fiber optics, electrical equalization is a
tried-and-proven concept. We will see more of it as our hunger for
bandwidth continues to outpace our ability to replace installed
low-bandwidth media. Fiber optic folks had the luxury of ignoring it
because fiber bandwidth was plentiful - until now.

I am asking if this idea is worth discussing.

Thanks,
Vipul

vipul.bhatt@xxxxxxxxxxx
(408)542-4113