Why re-invent the wheel - if you are only interested in getting odd bits of data out of the RPi as Nick says go buy a module (where the LoRaStack is taken care of for you!) supporting AT type messaging - there are lots available and are relatively cheap (note use a LoRaWAN module not a LoRa radio module!). At this point posters often say , aahh! but I am keen to learn and do my own stack/variant, in which case to borrow the old Irishman to lost Tourist joke - I wouldnt start from here - RPi is not a good platform to lean how to code a LoRaWAN stack for ^above reasons noted. 