| The Internet of Things technology has significantly improved the way people work and live,and raised production efficiency and service quality.However,limited by space,environment and other factors,it is difficult to set up land communication base stations in remote areas such as deserts,oceans and forests to provide corresponding services for Internet of Things terminals.With its advantages of wide area coverage,seamless connectivity and high-speed communication,satellite communication has become a reliable choice for iot terminals located in remote areas to access network services,and the satellite iot constellation with global coverage has become a strong complement to the terrestrial iot.However,when mass terminal devices are connected to the satellite Internet of Things,the existing technology cannot meet the demand of system throughput.Moreover,due to the long and open satellite communication links,the security of data transmission is difficult to be guaranteed for the services with high security requirements.Aiming at the development trend of satellite Internet of Things in the future,this thesis takes mass access of satellite Internet of Things terminal as the background,introduces the idea of overlapping transmission and access control,and proposes a hybrid multiple access technology.The details are as follows:To solve the problem of low throughput of traditional random access protocol,a hybrid multiple access scheme is proposed.This scheme uses the control ability of spread spectrum code on power spectrum density to construct non-orthogonal access conditions in power domain to realize overlapping transmission.The system capacity is improved by the iterative receiving of the receiving end to realize the non-orthogonal signal access.Firstly,the system model is described,and the workflow of the transmitter is illustrated.Then,the theoretical analysis and simulation of access performance are carried out,and the throughput and packet loss rate are compared with the traditional random access protocol.The simulation results show that compared with the traditional random access technology,the hybrid multiple access scheme increases the system throughput and improves the system access performance.The design and performance analysis of receiving scheme under mixed multiple access system are carried out.The scheme uses the low spectral density characteristic of spread spectrum transmission and the quasi-orthogonality between non-spread spectrum data packet and the conventional data packet to cover spread spectrum data packet.Iterative interference cancellation technique is introduced to separate mixed signals at the receiving end.Firstly,the concrete flow of the receiving scheme is introduced,and the feasibility of mixed signal separation at the receiving end and the safe transmission capability of the access scheme are analyzed and verified by simulation.The simulation results show that the mixed signal separation scheme can realize the separation of mixed signals,and verify that the mixed multiple access scheme can ensure the safe transmission of signals.Based on the mixed multiple access scheme,the load estimation algorithm and access control technology are introduced to the channel and subband segmentation frequency band utilization in the actual system,and the mixed multiple access scheme based on access control is proposed.Firstly,Vogt load estimation algorithm is used to dynamically monitor and evaluate the system load.Then,according to the load estimates corresponding to different service requirements,the access modes and resource allocation modes of different subbelts in the distribution system are optimized to maximize the utilization of available resources.The simulation results show that the load estimation algorithm and access control technology can effectively improve the system performance and resource utilization. |
