Research On Enhanced Access Technology Based On CRDSA In Satellite Communication System

The Internet of Things is a major application scenario for the next-generation mobile communication system which is called 5G.Because of the wide coverage and are not susceptible to natural disasters,Satellite IoT,which combines satellite communications with Internet of Things,has rich application prospects,such as smart grid monitoring,environmental monitoring,and disaster emergency response..One of the characteristics of the Satellite IoT is that there are a large number of devices in the network,but not every node device needs to connect to the network at all times.Therefore,the traditional fixed-distribution multiple access method(such as TDMA)is not applicable in this massive amount of competitive access.In order to improve the throughput under high link load in the satellite IoT scenario,on the basis of CRDSA,this paper proposes a DSCRDSA access scheme based on spread spectrum enhancement.First,the scheme uses each of the to-be-transmitted user terminals to send two copies carrying the same payload information and spread using the same spreading code,then select two different time slots when each frame arrives in the DS-CRDSA system.Iterative interference cancellation technology is adopted at the receiving end,and the solved replica packet is used in each iteration to eliminate the interference caused by another replica packet.Simulations show that DS-CRDSA has improved the system's throughput at high link loads compared to CRDSA.Then,for the problem of DS-CRDSA which is the throughput of high link load decreases rapidly with the increase of load,two different access optimization schemes are proposed.Both schemes determine the access threshold through adaptive traffic load so as to control the number of access users to ensure the stability of the system.The two schemes differ in that they employ two different strategies for obtaining link load and estimating link load.Finally,considering the hybrid connection scenario in the satellite IoT network,the high-priority users more sensitive to delay are regarded as the focus of random access optimization.For different priority services,all the time slots of one frame are also divided into the same number priorities to characterize different businesses.Based on the traffic load estimation algorithm,the priority-based TLE-DS-CRDSA is proposed.The system simulation shows that the proposed scheme can effectively guarantee the access success rate of high-priority services.