Doppler Estimation and Compensation Techniques in LoRa Direct-to-Satellite Communications

Within the Low-Power Wide Area Network (LPWAN) framework, the Long Range (LoRa) modulation adopted by Long Range Wide Area Network (LoRaWAN) technology has garnered significant interest as a connectivity solution for Internet of Things (IoT) applications due to its ability to offer low-cost, low-power, and long-range communications. One emerging use case of LoRa is direct-to-satellite (DtS) connectivity, which extends coverage to remote areas for supporting IoT operations. The satellite IoT industry mainly prefers Low Earth Orbit (LEO) because it has lower launch costs and less path loss compared to Geostationary orbit. However, a major drawback of LEO satellites is the impact of the Doppler effect caused by their mobility. Earlier studies have confirmed that the Doppler effect significantly degrades the LoRa DtS performance. In this paper, we propose four frameworks for Doppler estimation and compensation in LoRa DtS connectivity and numerically compare the performance against the ideal scenario without the Doppler effect. Furthermore, we investigate the trade-offs among these frameworks by analyzing the interplay between spreading factor, and other key parameters related to the Doppler effect. The results provide insights into how to achieve robust LoRa configurations for DtS connectivity.