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GNU Radio LoRa PHY level receiver & transmitter
(sh.itjust.works)
Research results on reverse engineering of the LoRa protocol and an implementation in GNU Radio. An open source LoRa PHY layer project provides access to the LoRa protocol for researchers and hobbyists.
Yes, SDR is less efficient than a specially designed radio chip, but what you gain is flexibility. With SDR, your radio can use any transmission encoding, you are mainly just limited by your polling rate.
Specially designed radio chips thrive in constrained, high-volume manufactured devices. However, for development purposes, being able to use LoRa with an SDR is an amazing step up.