Research On The Application Of LoRa Physical Layer Technology For Satellite IoT

The Internet of Things(IoT)uses sensors and communication technologies to connect devices with the Internet to achieve intelligent management and monitoring of devices.With the development of the IoT,its application range is becoming wider and wider,and it plays an important role in many fields such as national defense,industrial production,environmental protection,smart cities,and transportation.However,in some specific areas,it is difficult to deployment and interconnect the ground IoT base stations due to space and environmental constraints.In order to solve this problem,it is necessary to build a satellite IoT system.For the technology adopted by the communication between satellite and the ground terminal,it is necessary to meet the Low-Power Wide-Area Network technologies.The LoRa(Long Range)technology,which has been vigorously promoted in the terrestrial IoT,meets this requirement.Therefore,this paper deeply studies LoRa technology,analyzes the adaptability of LoRa technology in low-earth orbit(LEO)satellite communications,and finds solutions for unsuitable places,which is of great significance to the construction of the satellite IoT.The key technologies of LoRa physical layer including its unique modulation method,frame structure,coding method and synchronization method are studied and simulated.Then combined with the characteristics of LEO satellite communications,the adaptability of LoRa technology in LEO satellite communications is studied.The main research results are as follows:1)The influence of frequency offset,time offset and phase offset on LoRa modulation is analyzed,and a synchronization algorithm that can estimate frequency offset and time offset at the same time is proposed.Next,refined spectrum estimation technology is used to improve the performance of the algorithm.The simulation results show that the algorithm can accurately and effectively estimate the time offset and frequency offset of the LoRa signal.2)The use of LoRa communication chip and Software Defined Radio(SDR)is studied,LoRa signal is successfully received using SDR,the synchronization and demodulation of LoRa signal are realized and verified.3)LEO satellite communications will produce a fast time-varying frequency offset affected by the Doppler effect.Therefore,the influence of the Doppler-rate on the LoRa signal reception is studied,and the Doppler-rate estimation algorithm is proposed.The simulation results show that the algorithm also has accurate and stable performance when the signal-to-noise ratio is low.4)Due to the wide coverage of LEO satellites and high requirements for network capacity,ICS-LoRa modulation technology has been studied,which can increase the communication rate of LoRa signals,reduce the length of data packets,and improve the network capacity.On the basis of ICS-LoRa,its interleaving method is redesigned,and further interleaved LoRa modulation is proposed,which can further improve the LoRa network capacity.