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adamgreig / labrador-ldpc

LDPC encoding and decoding for Labrador
MIT License
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Request for documentation examples for usage of `llrs` #2

Open goblin opened 4 years ago

goblin commented 4 years ago

It would be quite handy if the documentation gave a real-world example of how to populate the llrs array from some actual data (i.e. received from a QPSK modem). Calculating them efficiently is not trivial, especially for large constellations.

Better yet, a function that takes the constellation points and received amplitudes as input, and produces the llrs on output, would be great to have.

adamgreig commented 4 years ago

I'm not sure if this is in scope for labrador-ldpc, though I agree it would be a useful thing to have in general. I've only really had to deal with BPSK or FSK constellations where it's very easy to generate the LLRs, so haven't had to think about doing it for QPSK or other n-ary constellations.

I'd be happy to add links to resources or examples to the repo, but I don't expect I'll have time to write any code for it any time soon.

goblin commented 4 years ago

Cool, thanks for the reply. I'm only learning about these topics, so not sure if I'm up for the task either. But if I get something working I'll definitely consider submitting a PR.

goblin commented 4 years ago

I found some information on this in section V (starting on page 11) of this progress report from NASA (IPN Progress Report 42-184, "Performance of Low-Density Parity-Check Coded Modulation" by Jon Hamkins, February 15 2011).