Study On The Task Scheduling Of Space Backbone Network Based On A Tracking And Data Relay Satellite System

The space backbone network plays an important role in space information network,as it is able to switch various types of traffic between space and ground users.The space backbone network can be implemented by extending the current running Tracking and Data Relay Satellite(TDRS)system,which is a trend in the development of the space information network.The task demands of space backbone network grow rapidly in recent years.However,restricted by construction costs and technical difficulties,the resources(e.g.bandwidth,access terminals)provided by a space backbone network are limited.It is essential to properly schedule the tasks so that the network resources can be used efficiently.The task scheduling problem in space backbone network differs itself from the counterpart in traditional TDRS system:(i)the tasks and terminal resources are more various.The space backbone network should support communication tasks with additionally equipped communication terminals;(ii)the space backbone network contains more types of resources.The resources of space backbone network include both bandwidth and terminals.A task will not be accommodated to the network when either type of the resources is exhausted;(iii)the tasks of space backbone network contains more windows.The source and destination users of a communication task can both be spacecraft.The dynamic access property of spacecraft users in a communication task will lead to more windows than that in tracking and data relay tasks.Based on the properties stated above,we study the task scheduling problem in space backbone network under different scenarios.The contents are listed as follows:1?The static task scheduling in space backbone networkWe study the static task scheduling in space backbone network with limited bandwidth and terminal resources.We first give an introduction to the properties of static tasks and devise an optimization model which maximizes the total profits of accommodated tasks.Then,we point out that the problem is non-deterministic polynomial and propose a Static Task Scheduling Algorithm(STSA)based on the genetic algorithm.At last,we verify the effectiveness of STSA through simulation analysis.2?The dynamic task scheduling in space backbone networkWe study the dynamic task scheduling in space backbone network with limited bandwidth and terminal resources.The problem is studied in two scenarios,according to the network resources utilization when a dynamic task arrives:(i)the available resources are sufficient to accommodate the arriving dynamic task(i.e.the task can be accommodated with no affection on others);(ii)the available resources are not sufficient to accommodate the arriving dynamic task.In the first scenario,we propose a Dynamic Task Scheduling Algorithm(DTSA),which minimizes the resources assigned to the dynamic task while balances the resource utilization of bandwidth and terminals.In the second scenario,we need to reschedule or even delete some of the pre-assigned tasks in order to maximize the total profits of accommodated tasks.We propose a Dynamic Task Rescheduling Algorithm(DTRA).The results show that DTSA and DTRA perform better than the state-of-art algorithms.3?The Static task scheduling concerning the bandwidth utilization of communication tasksOn the basis of our first work,we further categorize the communication tasks into singleuser tasks and converged tasks.We propose two algorithms named Task Scheduling Algorithm With bandwidth sharing(TSAW)and Task Scheduling Algorithm withOut bandwidth sharing(TSAO)to schedule the tasks with and without bandwidth sharing respectively.The simulation results show that STAO and TSAW achieve higher profits of accommodated tasks than DTSA.