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As an emerging wide area network technology, LoRa has the characteristics of low power consumption and wide coverage.It has very broad prospects in the field of internet of things applications.In recent years, it has been deployed in countless objects around the world.The advantages of wide coverage of low-orbit satellite networks make it an inevitable technology to achieve global coverage of massive internet of things.Firstly, the basic principles of LoRa technology were expounded.Then the problems existed after the LoRa technology was directly introduced into the low-orbit satellite IoT were analyzed.Finally, a set of LoRa transmission technology suitable for low-orbit satellite IoT was proposed, focused on solved the problem of LoRa frame synchronization under the condition of low-orbit long-distance low-power transmission, and the problem of LoRa demodulation caused by the high-speed movement of satellites due to the Doppler frequency off set.The simulation results showed that the proposed joint synchronization and frequency off set estimation algorithm could obviously improved the synchronization probability and transmission reliability of LoRa technology under the conditions of extremely low SNR and large Doppler frequency shift.

How to extend the HARQ technique to made it suitabled for LEO satellite communication network was explored.First the traditional HARQ technology was expounded.Based on this, the HARQ scheme based on low density parity check code (LDPC) and the HARQ scheme based on message group check code (BCC) were studied respectively, the performance of the schemes was analyzed through simulation.Finally, suitable feedback schemes were analyzed for the retransmission units in the HARQ retransmission mechanism, which provided some reference for the research of HARQ technology in LEO satellite communication networks.

Using the characteristics of satellites in diff erent orbits to build a more effi cient multilayer satellite network has become a hotspot in satellite network research in recent years.Traditional satellite network access methods have been unable to meet the needs of multilayer satellite networks with low latency and fl exible access, so it is urgent to design an effi cient random dynamic access protocol for multilayer satellite networks.This paper fi rst summarized the traditional satellite network access technology, clarifi ed the development context of the satellite network random access protocol, and then proposed diff erent low latency for the two diff erent scenarios of ground station access to satellite and multilayer satellite network intersatellite access.The access method could provided a reference for the development of the dynamic access technology of the multilayer satellite network in the future.