First Flight-Testing of LoRa Modulation in Satellite Radio Communications in Low-Earth Orbit

Abstract

At present, the use of LoRa modulation in satellite radio communications and the construction of a CubeSat constellation for the satellite Internet of Things based on LoRa technology has already begun. However, the limits of applicability of LoRa modulation in low-Earth orbits have not yet been established. This paper presents the results of the first flight tests of LoRa modulation for robustness against the Doppler effect in the satellite-to-Earth radio channel, carried out using a NORBY CubeSat operating at 560 km. Flight tests confirmed the very high immunity of LoRa modulation to the Doppler effect for modes with spreading factor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SF</i> ≤ 11 and spread spectrum modulation bandwidth <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BW</i> >31.25 kHz. LoRa modulation in these modes can be used in satellite communication without any limitations caused by the Doppler effect. For <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BW</i> = 31.25 kHz, the LoRa radio channel is affected by the static Doppler effect. Communication with the satellite is possible in this case only at high elevation angles. For <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SF</i> = 12, the dynamic Doppler effect becomes significant, and communication is possible only at low satellite elevation angles, which leads to the formation of a “hole” in the center of the coverage area directly below the satellite. In both cases, the duration of the communication session is significantly reduced because of the Doppler effect. In the case of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SF</i> = 11 and 12 at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BW</i> = 31.25 kHz, both static and dynamic Doppler effect catastrophically affect the LoRa radio channel, so that communication with the satellite becomes impossible.