Low-Power Satellite Access Time Estimation for Internet of Things Services Over Nonterrestrial Networks

The evolution of nonterrestrial networks (NTNs) will require some conceptual changes in the communication paradigm established in common cellular and low-power networks. This will be paramount in sparse low Earth orbit (LEO) satellite constellations that cannot ensure service continuity. Limited satellite access time for terrestrial devices and the typical Internet of Things (IoT) duty-cycled application will require coordination mechanisms, so that desired sleep and wake-up periods can be synchronized with satellite availability. Toward this coordination, this work first characterizes the access time of LEO satellites for terrestrial devices. It then evaluates the model proposed by 3GPP for orbit determination, the simplified general perturbation 4 (SGP4), in terms of accuracy and energy saving from the low power point of view. From the evaluation, a novel method is proposed based on relaxing the periodic updates of satellite orbital information required by SGP4 to increase the battery life of IoT-NTN devices. The method is enhanced with a function that matches the uncertainty in the access estimates to a wake-up guard time, improving, and guaranteeing access success. Finally, the proposal is validated using data from a real communication link between a terrestrial device and the Enxaneta LEO CubeSat (3B5GSAT).