Research And Implementation Of MAC Protocol For Satellite Ad Hoc Networks

With the continuous development of the space-air-ground integrated network,the number of satellites running in various orbits is increasing,making it possible to form satellite ad hoc networks.Compared with a single satellite communicating directly with the ground station,the advantages of the satellite ad hoc network lie in wider coverage area,higher flexibility and stronger scalability.Due to the high dynamics of satellite ad hoc networks and high requirements for service quality of service(Qo S)in many scenarios,the key to successfully building satellite ad hoc networks is designing a medium access control(MAC)protocol suitable for specific scenarios.In view of the needs of specific satellite networking scientific research projects,we analyze the feasibility of jointly forming a star network with medium and low orbit satellites,and design a MAC protocol with a multi-priority mechanism based on Time Division Multiple Access(TDMA).To further verify whether the relevant protocol meets the project requirements,we design a hardware-in-the-loop simulation platform,The detailed work of this paper is as follows:Aiming at the application scenario with the medium orbit satellite as the master and low orbit satellites as slaves,we propose a master-slave satellite ad hoc network MAC protocol based on TDMA.Firstly,the feasibility of forming inter satellite link between the medium orbit satellite and low orbit satellites in Walker Constellation is simulated and analyzed in target scenario.Then the MAC protocol is designed in detail for this scenario,including TDMA time frame division,data frame transmission mechanism,time synchronization mechanism,dynamic multi priority algorithm and so on.Finally,the performance indexes such as the time of slave node in the network,service delay,network throughput,and packet loss rate of each priority service are preliminarily analyzed.The results show that the protocol can make the nodes access the network effectively,guarantee Qo S of different priority services and optimize the "hunger" phenomenon of low priority services.Aiming at the problems of high cost,high risk and difficult scene reproduction of air-space network protocol,a hardware in the loop simulation system is designed based on the research requirements of satellite networking scene and networking protocol in this paper.We focus on completing the physical nodes and verifying the proposed MAC protocol on the system.Firstly,the overall design of the hardware-in-the-loop simulation system is introduced.Then,the design and implementation of the physical node based on FPGA is emphasized,including the MAC function of the programmable logic(PL)side,the dual network port forwarding function of the processor system(PS)side and the inter-satellite link simulation module.Finally,we carry out a communication function test on the physical node running the networking protocol.The results show that the realization of the MAC protocol and the physical node can meet the project requirements.