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RE: PAM-5 at 5 Gbaud


I am glad to discuss with you again.  It is always enjoyable.

Responses to your questions:

1. PAM-5 Symbol period.

There are two clear PAM-5 waveforms on HSSG reflector.

One of them is in page 7 (PAM-5 5 G Baud Modulated Laser Output), and page 8
(Zoom Modulated Laser Output) of  "10 Gb/s PMD Using PAM-5 Modulation by
Oscar Agazzi in January.

The zoomed modulated laser output picture has a very clear waveform of three
transitions per each 200 ps, which is 1/(5 G Baud).

The another picture is in page 31 of your Tutorial presentation "MAS
Techniques for 10 GbE".
This picture is clear but in 60 M Baud rate, and the timing scale is not
clearly denoted. I am not clear of this picture regarding its timing scale.

2. Bit Error Rate.

The system bit error rate involves every components including receiver and
others, and it is also affected by the data recovery technique.  PAM-5
requires not only the timing information of each bit, but it also requires
the voltage level information of each bit, together, to correctly recover
the data.  The "double requirements" will make it harder to recover
correctly, than a straight forward "timing information" only requirement.

However, if a link has a very reliable recovery technique and circuit, it
can achieve the target BER without any problem.  All we need is keep working
on it to come out with a right solution.

The BER issue is not a absolute issue, rather it is depending on how much we
like to pay to achieve the target BER.


Edward S. Chang
NetWorth Technologies, Inc.
Tel: (610)292-2870
Fax: (610)292-2872

-----Original Message-----
From: owner-stds-802-3-hssg@xxxxxxxx
[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Rich Taborek
Sent: Saturday, February 26, 2000 2:41 AM
To: stds-802-3-hssg@xxxxxxxx
Subject: Re: PAM-5 at 5 Gbaud


I heartily agree that proof of the general principles of MultiLevel
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
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
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
> (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
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
> simultaneously from the 1.25 G baud receiving signals to meet 10^-12 BER
> 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
> assurance.

Coding may be employed in MultiLevel signaling schemes to increase the
BER to a value required to meet link BER objectives. This has been presented
several HSSG presentations included those noted immediately below. It is
generally more cost effective to deploy coding to enhance the diminished raw
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
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
the existence of a full-duplex link. Relatively slow changes in slope
such as those associated with temperature changes can be readily and
tracked with the same feedback system operation with a low loop bandwidth.
Calibration principles were introduced in the MAS tutorial (link below)
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!