Cell Relay Archive

[nobody <nobody@web.onecall.net>]

quoth Terry:
> I Quote the XDSL-faq:
> 
> "The scrambler is very important.  It randomizes the signal so an
> adaptive equalizer in the remote modem can build the inverse channel
> response (including the transmit filter)."
> 
> How is this? In what way do the the adaptive equalizer benefit from the
> signal being scrambled?

Roughly speaking, the adaptive equalizer attempts to cause the received
power spectrum (after equalization) to be the same as the power sectrum
that the modulator would produce (before the transmit filter) _if_ the
data stream was perfectly random.  The actual power spectrum at the
can be very different from this if the input data are correlated.

If the actual user data were perfectly random, you wouldn't need a
scrambler.  Since it often is not, a scrambler is needed in order for
the equalizer to work.

nobody