Study On Random Access Preamble Design And Detection Algorithm For 5G Satellite Mobile Communication System

The vigorous development of the fifth generation mobile communication system has brought an opportunity and power to build the strategic network blueprint of integrating the sky,sea and land.The cooperative development of 5G technology and satellite mobile communication has become the general trend.Among them,LEO Mobile Satellite System with the advantages of wide coverage and small propagation delay plays an important role in the future space earth integrated communication network.As one of the key technologies of 5G new radio(NR),random access technology is the key premise for users to complete the uplink initial synchronization and effectively establish the satellite ground data transmission link.Due to the characteristics of satellite communication,such as long transmission distance,wide coverage,large time delay,large attenuation and limited load,the existing land random access scheme can not be directly applied to satellite mobile communication system.It is necessary to further study the problems existing in random access technology according to the complex channel environment of satellite communication system.Therefore,this thesis takes LEO Mobile satellite communication system as the research background,aiming at different communication scenarios,from the random access preamble sequence design,random access preamble sequence detection algorithm two aspects of high dynamic environment random access technology research.The specific work is as follows:First,in view of the shortcomings of the land preamble sequence,combined with the characteristics of satellite communication,in the communication scenario of unknown user location,a multi-root cascaded preamble sequence MR-CLS which is robust to carrier frequency offset(CFO)is designed.According to the requirements of user arrival uncertainty and subcarrier spacing in the beam,a long preamble sequence is constructed by cascading several short ZCS robust to CFO to meet the long-distance transmission and suppress the CFO in advance.And then,Using the designed MR-CLS sequence,a low complexity detection algorithm is proposed,which is completely robust to CFO and can flexibly adjust the length of correlation sequence to suppress noise.The simulation results show that the timing estimation performance of the proposed algorithm is more accurate in low SNR,and can effectively complete one-step TA estimation.Second,in the communication scenario where the user's position is known,the pre-compensation of the maximum round-trip delay and Doppler shift is analyzed according to the known position information and satellite ephemeris,and the format of the preamble sequence is reselected.And then,for multi-path fading channel,a joint clustering detection algorithm independent of threshold design is proposed from the perspective of data characteristics.The algorithm can achieve better timing detection performance and complete timing estimation in low SNR compared with the traditional detection algorithm based on threshold design.According to different communication scenarios,the above research work innovates and realizes 5G satellite random access technology from two aspects of preamble sequence design and sequence detection algorithm,which provides certain theoretical and technical support for the future global Internet of things and the construction of space earth integrated network.