Research On Random Access Protocol For Satellite Internet Of Things

With the rapid development of the Internet of Things,transportation,logistics,medical,functional environment and social networking are the main applications of the Internet of Things.Worldwide Internet of Things will be realized in the near future.However,the current terrestrial Internet of Things also has certain restrictions.It is difficult to place IoT nodes or base stations in a series of areas such as deserts,oceans,and forest areas where people are sparsely populated or difficult for humans to reach.In order to solve this problem,the concept of satellite Internet of Things came into being.However,a large number of users who do not continuously send short bursts have also presented new challenges to the access technology of satellite IoT that how to solve the problem of collision and interference between users when a large number of low-cost terminals access the network at the same time.Therefore,it is necessary to design an applicable access protocol for the satellite IoT service.This paper first introduces the development status of satellite IoT and access protocols used in satellite IoT.Through the analysis of the research status at home and abroad,the advantages and disadvantages of different technologies are found,and the conclusion that the performance of the access protocol is directly related to the network load is obtained.Through the research and analysis of the background,this paper divides the satellite IoT into scenes with sink nodes and scenes without sink nodes,and gives a load estimation algorithm suitable for satellite IoT scenarios,which will be used to improve the performance of the access protocol.Secondly,this paper studies the scenes with sink nodes and proposes a slotted random access protocol based on Walsh codes.The multi-user access interference is eliminated by the orthogonal performance of the Walsh code,thereby improving access performance.In addition,considering the additional bandwidth overhead caused by the introduction of the spread spectrum code,in order to further save resources without reducing the performance,this paper introduces a load estimation algorithm to improve this protocol,and obtains a dynamic Walsh Code slotted random access protocol based on load estimation.After that,this paper studies the scenes without sink nodes.According to the characteristics of the scene,an asynchronous random access protocol based on Gold code is proposed.In order to improve performance,satellites are required to send access permission signals periodically to approximate the effect of "slotted".After the load estimation algorithm is improved according to the characteristics of the non-aggregation scenario,it is applied to this protocol,and a new dynamic Gold code asynchronous access protocol based on load estimation is obtained.Finally,considering the practical application scenarios of satellite IoT,this paper studies the multi-service compatibility of the protocol,and proposes a Gold code random access protocol based on service classification.Based on the classification of satellite IoT scenarios,the slotted random access protocol based on Walsh codes and the asynchronous random access of Gold codes are proposed for the scenes with sink nodes and without sink nodes respectively.The protocol introduces the idea of load estimation algorithm and service classification separately to further improve the access performance and multi-service compatibility of the protocol.