Thanks Bill, I'll definitly dive into that. After figuring out what the current octave code is and isn't doing I generated a 2/3 rate code (696 code bits, 434 data, 232 parity) and got the mode 6000 unittests working with it. I actually used a LDPC code generator I wrote a few years back when I was looking into them the first time. (But never got around to actually finishing it). It probably is not the best code, but at least I can start testing on air again and if needed replace the code later.
As for making the modem softdecission what exactly is the range run_ldpc_decoder() expects. I see that the 'fixed' bits use -10.0. Is the value of the bits important or is it completly relative? Regards, Jeroen On 06/13/2020 07:31 AM, 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 > > > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > <mailto:[email protected]> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2
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