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RE: Fade remover



Franklin,

Unfortunately the CDP1802 CPU with 64k bytes ECC RAM running at 100K
instructions/s in IHU-1 doesn't have the resources to handle the FEC
and/or interleaving tasks.  It was a deliberate decision to stick with
the tried and true technology for IHU-1.  IHU-2 has the capacity but is
not being used.

Right now the best solution is to convince the command team to transmit
every 514 byte blocks three times in a row.  This is an extreme case of
interleaving and would allow us to vote on each bit before assembling a
frame.  The only problem is synchronizing the three block sets in the
face of lots of bit errors but some sort of correlation function should
be able to handle that.  The advantage of this approach is that it is
the only way to get some form of error correction implemented in the
existing IHU-1 that is also backward compatible with existing hardware
and software. (NOTE: I didn't think this up - it was W3IWI's idea.)

Command team, are you listening?  With this and the USNA 40-foot dish we
have fully dedicated to AO-40 we could deliver some good data frames
whenever AO-40 is above the horizon!

Rick
W2GPS

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Franklin Antonio
Sent: Friday, February 02, 2001 6:26 PM
To: dg1kjd@afthd.tu-darmstadt.de
Cc: Brian Mitton; amsat-bb@AMSAT.Org
Subject: Re: [amsat-bb] Fade remover


At 03:15 PM 2/2/01, Jens David wrote:
>Again, it would be nicer if we had some sort of convolutional FEC on
the
>signal. We could use some soft-output modified viterbi decoder (the
BCJR
>for example) to consider the reliability of each symbol from each
source
>and weighting them appropriately before adding them up.

Yes, but it's even more than that.  If you had good error-correcting
coding
and interleaving on this link, you would have greatly reduced
susceptibility to fading, and single stations would decode the data
correctly by themselves and you wouldn't need to do the combining.

System engineering is the best answer.


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