Research And Design On Random Access Scheme For 5G Based Leo Satellite Communication System

The integration of satellite communication system and terrestrial communication system has attracted increasing attention in the field of the sixth-generation mobile communication technology.Compared with medium-and high-orbit satellite,low satellite has become effective extension of territorial communication system with its mature technology,low delay,full coverage and low cost.The current research on low-orbit satellite communication system focuses on the deep integration of 5G key technologies,enabling satellite communications.As one of the key technologies of 5G,random access is the basis for establishing uplink and realizing data transmission.Due to the high transmission delay and large frequency offset,the existing 5G random access technology cannot be directly applied in the low orbit satellite communication system.With this as the background and 5G random access technology as the starting point,this paper conducts research on the random access of low-orbit satellites,which mainly includes three aspects:the design of the preamble,the detection of the preamble and the preamble conflict detection.Firstly,considering the high delay and large frequency offset of satellite communication,a kind of robust preamble for satellite communication is designed.Firstly,the round-trip transmission delay difference is introduced as the time uncertainty in the satellite beam,and the preamble duration design is given according to the territorial preamble design criteria.Then,for the sequence part of the preamble,the single-segment sequence design and the multi-segment sequence design are given and the shortcomings of the single-segment sequence design are pointed out.Then,the multi-segment sequence design is optimized from two aspects:high delay detection and frequency offset elimination.Finally,the three proposed sequence designs are simulated and evaluated to show the performance superiority of the multi-segment sequence design more intuitively.Secondly,based on the proposed satellite preamble,a satellite preamble detection algorithm is studied.The algorithm includes three aspects:transmission delay difference detection,frequency offset effect elimination and multi-user peak detection.Firstly,based on the proposed preamble design,the transmission delay difference is divided into two parts:the fractional delay difference and the integer delay difference.Then,get the correct peak positions and eliminate the influence of frequency offset on detection through two ways of peak detection.Then,considering the multi-user access scenario,the transmission delay difference of different users was calculated by cyclic searching of the peak location set.At the end of this chapter,a simulation platform is built to simulate the transmitting and receiving of the preamble.In terms of time delay detection,anti-frequency offset and other aspects,a comparative work is made with the existing detection algorithms to further show the reliability of the detection algorithm designed in this paper.Thirdly,the random access collision detection algorithm is studied.Considering the characteristics of high latency in satellite communication scenarios,the two-step random access process is proposed in the industry,and the advance completion of conflict detection can be better applicable to the two-step access process.Firstly,the conflict detection scheme in 5G terrestrial cellular system is introduced.Then,the existing M2M collision detection scheme is studied and applied to the satellite preamble and the shortcomings of the scheme are pointed out.On this basis,a conflict detection scheme based on the tag sequence is proposed.Finally,the performance superiority of the proposed conflict detection scheme is verified by simulation.