[10GBT] Executive summary of issues with PAM12
Here’s an executive summary of the issues we’ve found with the PAM12
proposal. For more details, please check the reflector e-mail message
entitled “Summary of issues with PAM12”.
For the same transmit launch voltage, the emissions from a PAM12 transmitter
will be 0.6dB to 1.1dB higher than that for PAM8.
2. Separation of Levels (Susceptibility)
For the same transmit launch voltage, the separation of levels will be 2.0dB
(at 100m) to 3.9dB (at 0m) lower for PAM12 than for PAM8. When combined with
the emissions issue above, the total EMI penalty will be between 2.6dB and
4.5dB for PAM12 over PAM8.
3. Hole in the Constellation
PAM12 uses a 12X12 2D constellation in which a 4X4 hole is carved out in the
center. This causes at least a 1.1dB loss in SNR margin for PAM12, and it
allows the link partner to vary the transmit power by upto 0.43dB.
4. Framing Complexity
PAM12 uses a complex framing scheme encompassing 33 LDPC code blocks,
instead of the 1 block scheme used in the PAM8 proposal.
5. Fixed Patterns
PAM12 uses fixed patterns to delineate data frames. These fixed patterns
convey no information whatsoever.
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