Research On Random Access For Short Packets In Satellite Terrestrial Integrated Network

Satellite-terrestrial integrated network has been widely concerned because it can solve the limitations of terrestrial communication network.One of the important services in the scenario of satellite-terrestrial integration is short packets,and its service transmission occurs after random access.At present,most of the research is independent of random access,so in order to realize efficient transmission of short packets,this thesis has carried out the related research on one-step joint transmission of random access preamble sequence and data,the main contributions of this thesis are as follows:Aiming at the problem of low transmission efficiency of short packets caused by the long delay of satellite-terrestrial link,from the perspective of data explicit transmission,based on compressive sensing theory,a sparse signal which can describe terminal state,channel state information and data simultaneously is constructed,the preamble has the same channel state information as the data is used,a compressive sensing model which can jointly detect active terminals,channel state information and transmission data is established,and a one-step grant-free random access scheme in which data is explicitly transmitted after the preamble is proposed.The simulation results show that the proposed scheme can achieve similar performance to the traditional two-step random access in active terminal detection,channel estimation and data recovery while reducing signaling overhead.Aiming at the problem of low transmission efficiency of short packets caused by the long delay of satellite-terrestrial link,from the perspective of data implicit transmission,based on the principle of full arrangement of lexicographical order,a preamble sequence cascade mode is designed,the mapping rules between cascaded preamble sequences and data are constructed,and a one-step grant-free random access scheme based on lexicographical order implicit transmission is proposed.The simulation results show that the successful probability of terminal detection can reach over 90%and the successful probability of data recovery can reach over 85%while reducing signaling overhead.Aiming at the problem of poor timeliness of timing detection in random access caused by high-speed satellite movement,based on the principle of ZC sequence timing detection,the influence of cyclic shift on timing detection results is analyzed,a timing detection algorithm based on cyclic shift compensation is designed,and on this basis,a grant-free random access scheme based on efficient timing detection is proposed.The simulation results show that the proposed scheme can achieve the performance similar to that of delay pre-compensation in terminal detection and data recovery while improving the utilization rate of preamble resources.