Research On LEO Constellation Design And Onboard Switching

With the development of satellite communication technology and the need for diverse service types,integrating LEO satellite communication network with terrestrial communication network,it is the trend that the constructing a seamless air-space-ground global communication system.During the design process of LEO communication system,satellite constellation design and onboard switching scheduling algorithm are two key technology which have a great impact on the whole system.The constellation affects coverage performance,link propagation,network architecture,service availability and total system cost and scheduling algorithm determines key specifications,such as onboard hareware consumption,transmission delay and throughput.In terms of LEO constellation design,this paper extends the polar street of coverage constellation design method to near polar situation and deduces a series of design formulations that can provide better coverage performance.Considering that existing constellation design methods don't take minimum ground elevation into account,this paper proposes a creative method of determining altitude and minimum elevation by analyzing the mutual relationship among link attenuation,minimum elevation and altitude,which is able to acquire optimal minimum elevation in the premise of satisfying satellite link margin.As for the unstable sunlight condition and unsteady long-term orbital elements of standard circular orbit,this paper proposes a LEO constellation design method that considers orbital characteristics.The method combines sun-synchronous frozen orbit with near polar SOC design and the resulting constellation is able to provide single continuous global coverage with stable sunlight condition and long-term orbit steadiness.In terms of onboard switch,by analyzing different types of switch fabrics,this paper selects CICQ crossbar onboard switch fabric on considering the requirement and limitations of onboard switch.Based on the analysis of the throughput decrease caused by round robin scheduling,this paper deduces the maximum throughput of round robin on hotspot traffic model and verifies its validation by simulation.Also,this paper proposes an advanced round robin scheduling algorithm based on single comparison of input queue length and waiting time of HOL.Adding a comparison of length and a comparison of waiting time of HOL,the proposed algorithm optimizes hardware scheduling time with the ensurance of the delay and throughput performance of the onboard CICQ switch.This paper also analyzes the comparison times of VOQ length in single scheduling circle and acquires the relationship between comparison times and throughput of the switch.The LEO constellation design method and optimized onboard switch scheduling algorithm is important for the development of domestic LEO satellite communication system.