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Dear Task Force members, Recently it has been proposed to change the sync pattern
(Preamble) from the periodic 101010 … pattern to a non-periodic “data-like”
pattern. I am afraid that this might affect negatively one of the main purposes
of having a preamble, clock recovery, as well as its associate parameter: the
locking time. As was pointedly stated in 3av_0805_effenberger_3.pdf, the periodic
101010… pattern is the “golden” pattern for clock
recovery and it also has the advantage that it does not discriminate between
any specific implementations, neither present nor future, which is a very good
feature for a Standard. Changing to a “data-like” pattern preamble will
clearly affect the locking time which will become longer, since the number of
transitions (or updates for the phase-locked-loop) will be less. In some situations,
where the BER (before FEC) might be marginal, it might even lead to catastrophic
failure of the clock recovery system. Regards, Jaime Kardontchik Kawasaki Microelectronics |