Research On Satellite Internet Of Things Access Technology

With the development of wireless communication technology,most of the users can get better quality of communication service.Terrestrial communication systems use advanced technologies and provide good services for users.However,the coverage area of terrestrial communication systems is very limited,and can't provide information transmission service for those users located in remote area or ocean.Satellite communications is a good choice.As the coverage area of a satellite is large,satellite communications plays a role as expansion and complement of terrestrial communication systems,and provides service for the users out of the coverage area of terrestrial systems.With the development of the terrestrial Internet of Things,the integration of the Internet of Things and the satellite network is inevitable.To meet the needs of the Internet of Things,satellite communication network faces the following problems: massive device access? low-power and low-frequency wake-up of devices? a large number of devices frequent short message update information.The above characteristics bring unprecedented challenges to the random access mechanism in the mobile communication system.In order to solve the problems faced by the random access mechanism in satellite Internet of Things,this thesis focuses on the problems of massive access and short message update of satellite Internet of Things,and deeply studies grant-free random access scheme and the receiver detection algorithm in the satellite scenario.The design and information age of random access.The specific research work is as follows:The basic theory of satellite random access technology is studied in this thesis.First,the existing random access technologies are introduced.By comparing ALOHA and its derivative technologies,this thesis studies the throughput and packet error rate of satellite random access technology..Finally,the relationship between the packet error rate and throughput of different access technologies and the channel load are simulated.Considering non-orthogonal multiple access random access,this thesis establishes the uplink and downlink model of scrambling coded multiple access in terrestrial wireless communication based on the scrambling coded multiple access technology,and then studies the model of message passing algorithms in scrambling coded multiple access systems.Different multiuser detectors for scrambling code multiple access are considered,including the traditional elementary signal estimator.Using the message passing algorithm,the probability model of the elementary signal estimator can be accurately expressed in the form of factor graph,which can be further optimized by subsequent algorithms.The simulation results show that,based on the scrambling code multiple access system,the performance comparison of two kinds of multi-user detectors is given,and the availability of scrambling coded multiple access as non-orthogonal multiple access is given.Considering the satellite scenario,this thesis proposes to further optimize the message passing multi-user detector in the scrambling code multiple access system based on the generalized approximate message passing algorithm.The traditional elementary signal estimator has good performance but high system complexity.On this basis,a messagepassing algorithm is proposed.The generalized approximate message-passing algorithm can solve the high-complexity problem of the message-passing algorithm.The method of expansion and Gaussian approximation realizes multi-user signal detection using only the channel matrix and the received signal.The generalized approximate message passing algorithm is well combined with the scrambling code multiple access system.The algorithm will further enhance the performance of the multiuser detector and reduce the iterative complexity of the multiuser separation in the received signal.Finally,the age of information(Ao I)of different random access is studied,and the Ao I can be used as a new parameter to judge the performance of random access technologies.The change of Ao I can be regarded as a Markov process,and one-step transition probability and steady-state distribution probability of Ao I of random access are derived and given in this thesis.The average Ao I of random access can be deduced through the stationary distribution,and the variation of the average Ao I of random access under different loads is simulated,and the simulation results are similar to the theoretical results derived,and the theoretical derivation can be used to guide random access.