David, I have quite a bit of code in this area from modem stuff from
years ago.
Mostly based on David Mackay's work from memory. I can dig it all out.
I generated :
LDPC matrix generator, parametizable.
C++ encoder, C encoder, encoders with precalculated LUTs that I used on
STM32L0 at 16 MHz ..
My decoder (soft) was all C/C++ for a processor with a bit of memory and
speed, mildly optimized.
But, depending on the code size, and rate rate, might work in a STM32.
It was all teamed up with a chirp + D^2-BPSK hybrid modem with an
optimized decoder ( and highly NEON optimized to run on an cortex A5
and keep up.
all is in a linux environment. I can dig out the LDPC stuff if ya like.
-glen
On 13/06/2020 3:31 pm, Bill Cowley wrote:
Hi Jeroen,
Further to David's reply, you might like to look at the AFF3CT
sitehttps://aff3ct.github.io/ which provides comprehensive info on
channel coding. David's codes have been Repeat Accumulate (RA) LDPC
codes - we used them initially as encoding is very easy (eg well
suited to a microController). Of course you probably don't need this
- so you might get slightly better performance with other options. I
haven't played with the AFF3CT software much, but it does cover RA.
Cheers, Bill
Cc:
Bcc:
Date: Thu, 11 Jun 2020 23:30:58 +0200
Subject: [Freetel-codec2] Generating LDPC code for 6000 mode
Hi,
The experiments with mode 6000 are going pretty well.
Another local HAM (PE1ITR) even managed to work our repeater with
just a
HackRF.
Compared to analog FM it seems to perform pretty well.
But I would like to take it a bit further and try to introduce
some FEC.
Since the currently used codec2 mode only needs 3200bps there is still
plenty of room.
I was thinking about a rate 2/3 code (687 code bits for 458 data
bits),
but I am a bit puzzled with the ldpc octave code.
How exactly do I generate the needed matrix (and ofcourse the C and
header files)?
Regards,
Jeroen
---------- Forwarded message ----------
From: David Rowe <[email protected] <mailto:[email protected]>>
To: [email protected]
<mailto:[email protected]>
Cc:
Bcc:
Date: Fri, 12 Jun 2020 07:29:34 +0930
Subject: Re: [Freetel-codec2] Generating LDPC code for 6000 mode
Hi Jeroen,
Hey that's great work with working the new mode on a HackRF, is that
about 50mW max?
Yes, FEC is a fine idea.
A friend has been kind enough to generate the codes for me,
however it's
not a process that is automated or straight forward. Couple of
options:
1/ Use an existing code.
2/ Use a code with more data bits than you require, and fill them with
known bits at the encoder and decoder that you don't transmit. This
effectively lowers the code rate a little. I do that for FreeDV 2020.
3/ Peruse the CML library codes and see if they have one that fits
your
use case, e.g. ldpcut.m
There is an Octave utility to generate .[ch] files and run the
codes in C.
Cheers,
David
On 12/6/20 7:00 am, Jeroen Vreeken wrote:
> Hi,
>
> The experiments with mode 6000 are going pretty well.
> Another local HAM (PE1ITR) even managed to work our repeater
with just a
> HackRF.
> Compared to analog FM it seems to perform pretty well.
>
> But I would like to take it a bit further and try to introduce
some FEC.
> Since the currently used codec2 mode only needs 3200bps there is
still
> plenty of room.
> I was thinking about a rate 2/3 code (687 code bits for 458 data
bits),
> but I am a bit puzzled with the ldpc octave code.
> How exactly do I generate the needed matrix (and ofcourse the C and
> header files)?
>
> Regards,
> Jeroen
>
>
>
> _______________________________________________
> Freetel-codec2 mailing list
> [email protected]
<mailto:[email protected]>
> https://lists.sourceforge.net/lists/listinfo/freetel-codec2
>
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Glen English
RF Communications and Electronics Engineer
CORTEX RF
&
Pacific Media Technologies Pty Ltd
ABN 40 075 532 008
PO Box 5231 Lyneham ACT 2602, Australia.
au mobile : +61 (0)418 975077
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