[opendtv] Re: Koetter-Vardy RS decoder (Mark's memo)
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 24 Nov 2004 16:10:36 -0500
By the bye, I think this isn't too hard to understand
intuitively (excerpted from the article quoted
previously):
---------------------------------
http://www.physorg.com/printnews.php?newsid=3D1906
Breakthrough in Coding Theory and Practice
[ ... ]
i.e., an algorithm that
fully utilizes the probabilistic information available
at the receiver. The Koetter-Vardy soft-decision
decoding algorithm results in substantial coding gains
in practice [up to 1.5 decibels on additive white
Gaussian noise channels, and much more on
Rayleigh-fading channels].
----------------------------------
DTT receivers of all types to date give poorer
performance in echo environments than they do when
only random noise is present. This can only be
happening because they aren't using the signal energy
available to them.
It seems obvious that if one has knowledge of the
distortion being introduced into a signal, at any
signal level, one should be more successful at
recovering from the distortion than if one has no
knowledge. With random white noise, there is no
particular rhyme or reason to the errors. That's
why they are called "random." It seems obvious
that if there's some sort of pattern to the
errors, even with very weak signals, they can be
fixed more successfully than signals where errors
are random.
Ideally, the *true* C/N margin required for
successful reception ought to be measurably lower
in Rayleigh and Ricean channels than in Gaussian.
By "true," of course, I mean that C/N is (C+I)/N,
rather than the more optimistic looking C/(N+I)
you often see quoted. (I is interference from
echo energy.)
Bert
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