LinuxSA Mailing list archives

  From: Jake Hawkes <jake@infinitylimited.net>
  To  : Daryl Tester <dt@picknowl.com.au>
  Date: Sat, 25 Nov 2000 18:56:30 -0700

Re: ADSL Enabled Exchange Areas: Updated 20/11/2000

Daryl Tester wrote:
> Which is where the 2400 baud comes in - it's pretty much the maximum
> bandwidth that you can squeeze out of a voice grade (3.3 Khz from
> memory, but I may be out by a few hundred Hertz here) due to Nyquist.
> Any bitrate over 2400 bps is done "by signalling trickery", like
> QAM and run length encoding/compression, but the _baud rate_ cannot
> exceed half the available bandwidth without sampling errors being
> introduced.  Yet people keep making the same mistake (on both sides
> of the fence) over and over again.

the way I remember, is that 2400 baud means 2400 symbols a second[1]. A
symbol may represent more than 1 bit, and with no "signal trickery", one
baud is on bit[2].

Then you get very clever "signal tricksters" doing some hoopy maths, and
you get constellation patterns, representing a bunch of bits, the more
clever the constellation, the more bits per baud[3].

Then, I believe more trickyness was brought in to do more clever things.

This is around about where my memory from 4th year digital
communications at the Levels peteers out...


--
Jake Hawkes B.Eng, (CSE)

theressomethignwrongwithmyspacebar


[1] this may or may not be true 
[2] this may or may not be true 
[3] this may or may not be true

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