Re: Equalization
Vipul,
I agree with you. Equalization can indeed overcome DMD with
an appropriate receiver that can handle the multipath problem.
The Equalizers used in the wireless industry for multipath tend
to be very complex and may not be implementable at 10Gbps.
However, simpler Equalizers can provide adequate performance.
The initialization of the Equalizer can be blind like in 1000 Base-T
i.e. the receiver does not need any training sequence. This prevents
the need for complex auto-negotiation. Also, the Equalizer can
automatically recalibrate so that it can adapt to any time varying
effects if such conditions should arise.
Regards,
-Sudeep
Vipul Bhatt wrote:
> 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