Towards an SDR implementation of LoRa: Reverse-engineering, demodulation strategies and assessment over Rayleigh channel

LoRa is a popular low-rate, Low-Power Wide Area Network (LPWAN) technology providing long range wireless access over unlicensed sub-GHz frequency bands to the Internet of Things (IoT). It has been used in many applications ranging from smart building to smart agriculture. LoRa is a patented modulation. However preliminary reverse-engineering efforts documented parts of it. In this article, we detail the different stages of LoRa transceivers: channel (de)coding, (de)whitening, (de)interleaving and (de)modulation with reverse-engineering in mind. Closed-form expressions for each of these stages are given, and different demodulation and decoding strategies are presented. This allows for a complete modeling of LoRa, which enables Software Defined Radio (SDR) implementations, as well as performance assessment under various channel conditions. These simulations show that LoRa systems have good properties for time and/or frequency selective channels (especially for the latter), thanks to the robustness of its underlying Chirp-Spread Spectrum (CSS) modulation.