Research On Task Scheduling In Space Data Relay Network

Space data relay network(SDRN),which has the characteristics of wide coverage and strong sustainable transmission capability,provides the data tracking,observing,contrling and relaying services for numerous low and medium orbit user satellites and deep space probes.Task scheduling in SDRN refers to the scientific and reasonable allocation of relay resources for the task transmission according to the task request and the payload of data relay satellite.In recent years,with quantities of satellites had been successfully launched,the contradiction between increasing space tasks and limited relay resources has become increasingly prominent,which has brought great challenges to the transmission of space data.Therefore,more flexible and efficient scheduling algorithms are urgently needed to ensure the reasonable allocation of relay resources and improve both of the capacity of task transmission and the using efficiency of relay resources.The main contents are summarized as follows:Firstly,aiming at the problem that the competition between emergency tasks and common tasks reduces the efficiency of task scheduling in SDRN,a real-time dynamic scheduling(RTDS)algorithm is proposed.In RTDS algorithm,the whole task scheduling process is divided into three parts: initial scheduling,dynamic scheduling and final scheduling.Under the constraints of antenna resources and transmission time windows,initial scheduling generates the scheduling scheme of the initial task set.Dynamic scheduling refers to the process of adjusting the initial scheduling scheme after emergency tasks arrived.The purpose of this behaivor aims to provide the relay resources which emergency tasks needed.Final scheduling means to select the scheduling scheme with highest task priorities and smallest task changes by multi-objective decision algorithm.Simulation results demonstrate that RTDS can effectively ensure the transmission of emergency tasks and improve the transmission efficiency of SDRN.Secondly,aiming at the problem of low scheduling efficiency caused by a large number of space tasks in SDRN,a task scheduling algorithm based on contact plan design(CPD-TSA)is proposed.In contact plan design,by quantifying the transmission rate and duration of inter-satellite link,the amount of user data that can be transmitted is obtained,and then the connection selection is designed according to the amount of user data.In the task scheduling,each relay resource establishes its task set based on the contact plan design.The time sharing graph is used to allocate reasonable transmission time for each task,so as to improve the flexibility of task scheduling.Simulation results show that the proposed CPD-TSA can effectively improve the task scheduling efficiency and the resource utilization of SDRN.