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[ax25-layer2] ECC vs. FCS

Rud Merriam k5rud at arrl.net
Fri Aug 4 02:47:52 UTC 2006

Phils one paper indicates that adding a RS FEC is a effectively 3db 
improvement, i.e. you can successfully decode a signal 3 db lower than 
without the FEC.

Montgomery County, TX

----- Original Message ----- 
From: "Samuel A. Falvo II" <sam.falvo at gmail.com>
To: "Discussion of Link Layer use of AX.25" <ax25-layer2 at lists.tapr.org>
Sent: Thursday, August 03, 2006 7:52 PM
Subject: Re: [ax25-layer2] ECC vs. FCS

> On 8/3/06, Glenn Thomas <glennt at charter.net> wrote:
>> I don't think so. The syndrome bits are part and parcel of the whole
>> package. If you just send the syndrome bits, and some of them don't
>> match the original syndrome bits, you can't tell which version is
>> correct! ...oh, if both copies are identical as received, you haven't
>> transferred any additional information. You have burned some
>> bandwidth without getting anything for it.
> Knowing that the syndrome bits are sent in a separate packet, what
> difference is there if I send the syndrome frame immediately adjacent
> to the intended data frame, or 30 seconds after?  The passage of time
> does nothing to the original bits of the data frame as received at the
> receiver.
>> The utility of ECC is something that can be established or refuted
>> for the Amateur radio environment by the statistical study I proposed
>> in an earlier posting.
> I believe Phil Karn already has performed these studies, and agreed
> that FEC is the way to go.  I cannot seem to locate those documents,
> however, so take that as a possibly failed recollection for the time
> being.
> -- 
> Samuel A. Falvo II
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