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Re: PAM-5 at 5 Gbaud


I heartily agree that proof of the general principles of MultiLevel signaling
need to be proven to an extent to remove any reasonable doubt of technical
feasibility by the July Plenary meeting. To this end, I would like all
proponents of MultiLevel signaling to put their best resources to work. 

I'll try to respond to some of the questions recently posed to this reflector
regarding PAM5 below. I don't mean to imply that all MultiLevel problems are
completely solved, only that solutions have been proposed, many of which have
been applied to other signaling technologies.

Edward Chang wrote:

1) PAM5 Symbol period

> For the timing part, the PAM-5 coding has maximum of three transitions in
> period defined by its baud rate.  For example, at the 1.25 G Baud data rate
> (800 ps period), within an 800 period, there are maximum transitions of
> every 266 ps, which is equivalent of 3.7 G Baud of a NRZ coding.

I may have missed something between you and Jaime here, but a baud interval
generally denotes a single transition (ignoring undershoot, overshoot, ISI,
etc.). The value of the symbol encoded during a baud period may have a binary
value for a binary encoded signal, or a quinary value, in the case of PAM5.
Therefore, at 1.25 Gbaud, the symbol period is 800 ps, not 266 ps. If you
believe this not to be true, please explain. 

2) Bit Error Rate
> As it was mentioned before, to recover the bit timing and level information
> simultaneously from the 1.25 G baud receiving signals to meet 10^-12 BER is
> not a easy job, which has not been proved in the field yet.  To assume a
> fiber will automatically achieve 10^-12 is a desirable objective, but not an
> assurance.

Coding may be employed in MultiLevel signaling schemes to increase the EFFECTIVE
BER to a value required to meet link BER objectives. This has been presented in
several HSSG presentations included those noted immediately below. It is
generally more cost effective to deploy coding to enhance the diminished raw BER
of a MultiLevel link than to than trying to attempt increase the raw link BER to
match the system BER via traditional means (e.g. Receiver Sensitivity
improvements, higher RIN lasers, etc.) (See references
to FEC)

3) Laser Linearity

Wenbin Jiang wrote:
> Laser linearity is one concern.  What about its slope efficiency variation
> with the temperature?

A Link Calibration procedure has been proposed which initializes the link
transmitter and receiver levels using a closed-loop feedback system enabled by
the existence of a full-duplex link. Relatively slow changes in slope efficiency
such as those associated with temperature changes can be readily and dynamically
tracked with the same feedback system operation with a low loop bandwidth. Link
Calibration principles were introduced in the MAS tutorial (link below) pages
42-56, 84.


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.             rtaborek@xxxxxxxxxxx <= NEW!
Santa Clara, CA 95008 <= NEW!