hamming (12,8) decoder source-code

[Kristoff]

Hi,


I've started on the dPMR decoder for C4FM. One of the things I that is
needed is a hamming(12;8) decoder as that is used as FEC for the CCH
(control channel).

Anybody any pointers to a good open-source implementation of this?


73
kristoff - ON1ARF

[ronald simpson]

Take a look at OP-25
http://op25.osmocom.org

That site has much open source code for mostly P25 but you may find what you are looking for.

While your at it maybe build a lightweight  P25 NAC decoder and put the source code out?

73,

Ron Simpson, N6GKJ

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[Kristoff]

Ronald,

On 2015-05-26 17:04, ronald simpson wrote:
>
> Take a look at OP-25
> http://op25.osmocom.org
>
> That site has much open source code for mostly P25 but you may find
> what you are looking for.
>

OK, I had looked at some other DV systems but not at P25. As far as I
can see in the source-code of DSD, P25 does use hamming (it seams to use
almost any technology out there: hamming, golay, reed-Solomon), but
concerning hamming, it uses shortened hamming (15,11,3) while dPMR uses
shortened (12,8).

For dPMR, I have been doing some reading on hamming-codes and I have got
an idea on how I may be able to do this. As I actually have a dPMR446
signal (1) that I managed to record, I now have a reference-signal on
which I can based myself and do some guessing-work and start coding.




(1)
Yes, I actually now have a dPMR signal that I manage to record. I
captured it while scanning the dPMR channels between 446.1 and 446.2.

However, as the quality of that recording is not that good, I am still
very much interested in good-quality dPMR signals, by preference from
radios of different vendors and using different audio-codecs. So if
somebody has a dPMR radio, feel free to capture some audio using a
receiver with a discriminator port or a RTL-stick and some SDR
application, it would be very good help if you could send it to me.

> While your at it maybe build a lightweight P25 NAC decoder and put
> the source code out?
>

:-)
I currently started working on dPMR and Fusion as these are signal that
are actually used here in ON-country and are very well documented.

If you want to do this yoursef, there already is a P25 decoder in DSD,
so that might be a good start for you. It's actually more a question of
cutting out stuff then writing new code. :-)

It's actually a very good exercise to learn what is *really* inside a DV
stream!





73
kristoff - ON1ARF

[ronald simpson]

My intent is to put a P25 NAC decoder on a PIC, then use that to build a function decoder based upon selecting different NAC id's. DTMF and CTSCC don't function well on P25

On May 26, 2015 2:17 PM, "Steve" <coupay...@gmail.com> wrote:

I guess the question is, after you reinvent the wheel, is what do you do with it?

Is there a demand for minicomputers doing what handheld radios do?

[Reuven Z Gevaryahu]

The newer parts of DSD use the IT++ library for doing this kind of thing.

As for C4FM decoding, you may want to get in touch with Eric Cottrell (WB1HBU I believe). Based on his posts (http://forums.radioreference.com/voice-control-channel-decoding-software/300904-yaesu-fusion-raw-audio-sample.html etc), he got C4FM voice and callsign decoding working in DSD back in November, but he hasn't got a chance to clean up/commit that to his git branch for DSD (https://github.com/LinuxSheeple-E/dsd). He also got DSD working with the USB3000, and was going to try the same for the ThumbDV, so that the more questionable MBELIB code could be avoided by those with proper hardware.

--Reuven (KB3EHW)

[Kristoff]

Reuven,


Very interesting pointer. Thx!

That IT++ library looks very impressive.


I will also try to contact Eric.


Thx!
kristoff - ON1ARF

[Luis Bernal]

Hi

Liquid DSP implements hamming 12,8 and its an Open source and pure C library

http://liquidsdr.org/doc/fec.html

[Kristoff]

Luis,


Thanks!
If we go on like this, I will have a luxary-problem that I do not know what library to chose from the different projects :-)


The liquidsdr website is really interesting. I now have a lot of reading to do!


Cheerio! Kr. Bonne.