A Two-User Successive Interference Cancellation LoRa Receiver with Soft-Decoding

LoRaWAN is a popular wireless technology that provides long-range connectivity to Internet-of-Things devices using a bit-interleaved coded modulation. To minimize their energy consumption, LoRaWAN end-nodes implement a pure ALOHA access scheme, which leads to collisions among users at the gateway and a reduced throughput in crowded networks. To improve the throughput of interference-limited LoRaWAN networks, we design in this paper a successive interference cancellation receiver that is able to decode frames from two colliding users with the same spreading factor. By performing both a soft-demodulation and soft-decoding to recover the message of each interfering user, the proposed two-user receiver explicitly leverages the coded spread spectrum modulation of LoRa. We show that the joint usage of interleaving and coding is critical to achieve a decent cancellation of the strongest user. Simulation results indicate that our receiver successfully demodulates the frames of two interfering users with a 1.5 dB difference of received powers, even at very low signal-to-noise ratios.