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Re: Equalization


I agree with you completely. I'm also optimistic that we can come up
with a workable equalization solution for multi-mode cable plants.
However, we should not defocus our efforts to meet HSSG objectives in a
manner which address all 5 PAR criteria in a timely manner.

Vipul Bhatt wrote:
> 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


Best Regards,
Richard Taborek Sr.                 Phone: 408-845-6102       
Chief Technology Officer             Cell: 408-832-3957
nSerial Corporation                   Fax: 408-845-6114
2500-5 Augustine Dr.        mailto:rtaborek@xxxxxxxxxxx
Santa Clara, CA 95054