Research On LoRa Waveform Adaptive Transformation For LEO Satellite Internet Of Things

The Io T application of terrestrial networks has gradually developed and matured,but in some large-scale,cross-regional,harsh environments and other fields,it is difficult to build and maintain terrestrial base stations due to limitations of space and environment.phenomena,such as data collection services in remote areas such as oceans,forests,and deserts.The satellite Internet of Things has become an effective supplement to the terrestrial Internet of Things due to its wide coverage,unaffected by weather and geographical conditions,and easy to provide network connection support for large-scale motion platforms.In the Io T technology system,the physical layer waveform design is the basis for realizing wide network coverage and low power consumption.The ground Io T waveform is designed for the quasi-static environment of the terminal,and the low-orbit satellite channel has the characteristics of high dynamics and has matured for the ground in recent years.The adaptive transformation of the Io T waveform has become a hotspot in the research of low-orbit satellite Io T.In this paper,in the traditional terrestrial LoRa system Io T,the low-orbit satellite high dynamic capture performance of LoRa waveform is poor,the Doppler frequency shift causes inter-sub-carrier interference caused by different sub-channel terminals,and the performance of LoRa traditional modulation and demodulation is deteriorated.In the high dynamic scenario of orbiting satellites,the adaptability of traditional LoRa waveforms is analyzed and an adaptive transformation method is proposed to improve the communication performance of LoRa waveforms in low-orbit satellite channels.The main research contents of the paper are as follows:(1)A Doppler frequency shift pre-compensation method assisted by terminal location information is proposed for the low-orbit satellite Io T based on the LoRa system to solve the problem of mutual interference between sub-channels under the high dynamics of low-orbit satellites.First,the probability density function of the Doppler frequency shift of the transmitted signal of the terminal is deduced considering the error of the terminal location information;further,the Doppler frequency offset prediction of the terminal is designed in the single-satellite and multi-satellite co-view access scenarios.Compensation algorithm;Finally,the performance of the proposed algorithm is simulated in the LoRa unlicensed frequency band and the L frequency band respectively.Compared with the Doppler frequency shift pre-compensation method of broadband terminals in the traditional satellite communication system,the method proposed in this paper can effectively alleviate the Interference between sub-channels improves system access performance.(2)In view of the deterioration of LoRa signal communication performance in high dynamic scenarios,this paper proposes a single/double differential LoRa modulation scheme.Compared with the traditional LoRa modulation scheme,which modulates the transmission information to the starting frequency of each symbol,this paper proposed modulation scheme will modulate the transmission information into the starting frequency relationship of two/multiple adjacent symbols,realize differential anti-Doppler modulation of the communication information,and derive the designed modulation scheme for low-orbit satellites.The communication performance expression under the channel,a maximum likelihood sequence detection demodulation and a low-complexity Viterbi demodulation algorithm are designed to optimize the error diffusion phenomenon of the proposed differential modulation scheme.The simulation results show that the proposed modulation scheme It improves the communication performance of traditional LoRa waveforms in low-orbit satellite high-dynamic channels.(3)The verification of the transmission process of the proposed scheme is realized through the USRP and MATLAB platforms,including signal transmission,capture synchronization,and solution of the entire communication process.Firstly,according to the software transceiver platform,the signal generation part and signal receiving part are introduced in detail,and the front panel and program block diagram of Lab VIEW are given;Chapter four presents the feasibility and effectiveness of the differential modulation scheme.