Enable Online LoRa Decoding Under Partially Overlapping Interference

In this paper, we reveal the existence of partially overlapping interference (POI) when multiple devices concurrently transmit in partially overlapping channels. Existing methods proposed for collisions in the same channel cannot achieve online decoding for target packets under POI due to unpredictable in-window distribution of interfering chirp. We instead propose PrLoRa, a novel method to achieve online LoRa decoding under POI. PrLoRa relies on the insight that only the target chirp is complete in the decoding window. Then PrLoRa adopts a novel operation named phase rotation which converts the difference in chirp's integrity to the amplitude change of energy peak after dechirp and Fast Fourier Transform (FFT). For energy peaks generated by the target chirps, their amplitude change is expected. To use phase rotation in decoding the target chirp, we first establish the theoretical model between amplitude changing and phase rotation, which can be used to infer the expected amplitude change of the target peak. In practice, the peak's amplitude suffers from the influence of channel noise, which causes decoding errors. So, we also propose a noise-aware window setting that can adaptively select the suitable window size for phase rotation according to channel noise. Furthermore, we propose the iterative phase rotation to cope with decoding errors caused by interfering chirps with confusing distributions. The Experimental results show that PrLoRa can reduce the SER by up to 0.92 compared with existing state-of-the-art methods.