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Re: Fade remover

I am in complete agreement with Franklin.  If we can
store twice the data that is one frame,  we can do a
tail biting  encoding of the data frame.  The interleaver
can simply be a computed pointer into this data, and
then you transmit it.  If we can't index through the
data at 400 bps, then we could build the array and
transmit it.  Therefore the total memory went from
514 bytes for the current load to 2028 bytes for the
worst case.  We could use exactly the
same demodulators we are using now, the data
rate would halve.  We could even use fairly long
constraint lengths if we tail bite.  This is absolutely
maddening to have 12 meter dishes in use and
getting not a single CRC checked frame.

Tail biting is where you write  the data to be encoded
on a "circular"  shift register the length of the data and
then pass the encoder around the circle until each
bit has been passed over once.  You can then glue
as many copies together of the transmission as you
need to decode.    Tail biting also relieves you of the
need to have a flush sequence.  This could be done.
It takes only will power.


----- Original Message -----
From: "Franklin Antonio" <antonio@qualcomm.com>
To: "Richard M. Hambly" <rick@cnssys.com>
Cc: <amsat-bb@AMSAT.Org>
Sent: Friday, February 02, 2001 11:05 PM
Subject: RE: [amsat-bb] Fade remover

> At 05:50 PM 2/2/2001, Richard M. Hambly wrote:
> >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.
> If you begin with the notion that you can never change anything, then by
> definition, you can never improve.  No technology would exist if everyone
> followed this sort of logic, so its a darn good thing that they don't.
> ENCODING an error-correcting code doesn't take much CPU.  It can be very
> simple.  The principles have been known about 30 years now.  Fear of
> error-correcting codes is irrational.

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