Research On Access Technology Of Low Earth Orbit Satellite Communication System

With the rapid and effective development of global communication technology,low-orbit satellites are widely used due to their advantages of global coverage,low orbital altitude,low delay,and small transmission power.And access technology is becoming more and more important as one of the key technologies in low-orbit satellites.Since the number of satellites used in low-orbit satellite communication systems is relatively large,the possibility of multisatellites coverage is relatively high.Users may appear in overlapping areas covered by many low orbit satellites.At the same time,communication services of user node are also developing towards diversification.Choosing different low orbit satellites to access will also have different access capabilities and different quality of service.So the problem of access under multi-satellites coverage is a meaningful issue worth researching.At the same time,with the rapid growth of the Internet of Things and mobile Internet,various types of smart terminals have emerged and proliferated.There are more and more application scenarios for mass connection using sensors as terminals.In some special areas,such as forests,seas,disaster areas,or desert areas that are not accessible,it is necessary to deploy very dense sensor nodes and use low-orbit satellites for data transmission in order to complete data collection.In fact,a sensor node has a small amount of information,called small data packets,and just need less transmission resources.A fast and reliable access transmission mechanism is needed so that each node can access the low-orbit satellite network for data transmission within a short period of time.Therefore,it is of great significance to study the transmission mode of the scenario where the ground-intensive nodes with small data packet services upload information to low-orbit satellites.In response to these problems,this paper studies related access technologies in low-orbit satellite networks.The concrete work is as follows:(1)Firstly,it briefly introduces the characteristics and composition of satellite communication systems,the features of low orbit satellite systems,typical systems,and some key technologies.Focusing on access algorithms for multi-satellites coverage in loworbit satellite communication systems and existing access methods and access procedures for satellite communications,and their inadequacies are analyzed.To lay down a solid theoretical basis for the proposed innovation of this paper.(2)The integrated weighted access algorithm does not study how the satellite should be accessed when it cannot provide the bandwidth requested by the user.Instead,the user's call blocking rate caused by the direct rejection of the user access.To solve this problem,the method of dividing priority and borrowing bandwidth is adopted,and an access algorithm based on comprehensive weighting and bandwidth borrowing is proposed in this paper.The simulation verified that the proposed algorithm can further reduce the user's call blocking rate.At the same time,the call access of high-priority users is well protected and the system performance is improved.Next,the proposed algorithm does not satisfactorily satisfy the required quality of service for services of the users who request to access,and an access algorithm based on comprehensive weighting and utility bandwidth borrowing which considers the utility of the system while borrowing bandwidth is proposed.And a simulation comparison and performance analysis have been conducted.This algorithm has also achieved good results in reducing the call blocking rate of the system while improving the total utility of the system.(3)There are too many signaling interaction processes,large signaling resource overhead and large access delay for the existing demand assignment access methods and the access process of the low orbit satellite communication system.It is not suitable for the scene where dense sensor nodes are deployed which have small data packets and need less resources on the ground to upload information to low orbit satellites.For this scene,this paper proposes a grant-free transmission mechanism which is based on resource occupancy graph and incremental triggering in short time.And it describes the specific implementation of this transmission mechanism in detail according to the four modules of incremental triggering in short time,resource mapping,grant-free access,and retransmission processing.And the superiority of each module's performance is also analyzed.The proposed access transmission mechanism fundamentally eliminates the access interaction process,saves signaling overhead and access delay,and also has an authentication function.It can avoid the competition and conflict of many nodes with limited resources,reduce the end-to-end delay,and improve the pass rate of service and resource utilization.