Resolve Cross-channel Interference for LoRa

Unlike existing studies that focus on intra-channel interference, in this paper, we reveal cross-channel interference when collided chirps with different bandwidths have the same slope in the time-frequency domain. Existing methods are inefficient in resolving this type of interference because the demodulation features they use rely on accurate time-domain distributions including the start and end time of all chirps, which is unavailable for uncompleted chirps within the limited receiving bandwidth. We propose SD-LoRa which utilizes the difference in collided chirps' time-domain distributions to identify the target chirp under interference. SD-LoRa adopts self-dechirp operation that maps the chirp's time-domain distribution to recognizable amplitude change of energy peaks that reflect the difference. However, for real received chirps, the amplitude change is unreliable due to the random phase drift and amplified channel noise. So we propose a phase correction method that uses the model between phase difference and the signal energy. We also design time-domain filtering that suppresses noise before self-dechirp. Finally, to avoid extra false energy peaks generated by self-dechirp confusing the demodulation, we separate chirps which cause peak overlapping into different groups and individually perform self-dechirp. The experiments show that SD-LoRa reduces the Symbol Error Rate (SER) by up to 88.6% compared with state-of-the-art methods.