Feels a bit like an advertisement here for Weightless-P. I assume you are involved? I've built an adaptive RS codec that runs very fast on Cortex-M. You'll want to update your PHY, though, to make the best use of any type of error correction. It's sort of odd to me that 802.15.4g -- and IIRC Weightless-P -- specify convolutional code FEC but then specify MAC frames that make them less effective than they should be. At least this is something LoRa gets right, even if (as I've been told) in present silicon there a glitches in some of the coding modes.
Anyway, you can find me pretty easily if you want to chat more, either through this forum or even by googling my username. I'd be happy to chat.