Study of Accumulated Doppler Effect on LoRa Symbols for LEO Satellite Communications

Thanks to its long-range, low-power characteristics, the LoRa modulation technique is being increasingly adopted for Low Earth Orbit (LEO) satellite communications with the Internet of Things (IoT) remote node terminals. However, with satellites reaching speeds of around $7.8 \mathrm{~km} / \mathrm{s}$, the LoRa symbols experience a frequency shift due to the Doppler effect which could result in packet loss. This study examines three linear models for evaluating the accumulated Doppler effect in a sequence of LoRa symbols, with a focus on higher spreading factors. The results demonstrate the maximum number of successfully received symbols without error caused by the cumulative Doppler shift per packet for different LoRa configurations, providing initial metrics for mitigation techniques and emphasizing the need for careful consideration of packet length in this communication scenario. Additionally, it was found that the difference in the predicted position of the first error symbol due to accumulated Doppler shift among the three models does not exceed one symbol unity.