## 2 Related Work  
### Space Information Networks  
The SIN is an important international scientific frontier and strategic commanding height in the world today. At present, the representative projects are the (Space Communications and Navigation (SCaN)) of the National Aeronautics and Space Administration (NASA) [11], the Transformational Satellite Communication System (TSAT) of the United States (US) [12], and the Integrated Space Infrastructure for Global Communications (ISICOM) of Europe [13]. SCAN plans to divide the network system into a backbone network, access network, spacecraft intranet, and adjacent network, which can adequately meet the needs of future space communications in the United States. Based on this framework, there is no need to build a new communication infrastructure for emerging tasks,which can effectively avoid duplication of construction. TSAT was proposed by the US Department of Defense in 2002. It consists of a space segment, terminal segment, and mission operation segment. The goal of TSAT is to adapt to the transformation of communication needs of the US military, break the communication bottleneck, and provide users with a secure and high-speed communication architecture. Although the TAST project eventually stopped, its overall architecture laid the foundation for the development of SIN technology. In September 2008, the European Union adopted a Security Council resolution on \"Making Future European Space Policy\", and the concept of ISICOM came into being. The ISICOM system consists of a space-based network and a terrestrial network. The goal is to establish an independent Internet Protocol (IP)-based communication network, which combines microwave and laser links to achieve broadcast services, emergency services, telemedicine, distance education services, and other services.  
Through the investigation and analysis of the current research situation of the SIN, according to the way of networking, the current SIN architecture can be divided into three categories: satellite-earth network, space-based network, and space-net-Earth network. Its typical system and main characteristics are shown in Table 1[14; 15].  
In conclusion, the space-net-Earth network architecture can make full use of the wide-area coverage ability and the abundant transmission and processing ability of the space-based network, and reduce the complexity and cost of the system technology; it is a more appropriate reference for the construction of the SIN.  
Aiming at the resource scheduling problem of the SIN, the current research mainly focuses on the resource scheduling of the GEO data relay satellite. [PERSON] used a backtracking heuristic algorithm to solve the resource scheduling problem of the GEO data relay satellite for the European Space Station [16]. [PERSON] studied the tracking and data relay satellite system (TDRSS) of the United States, and studied the scheduling problem with two visual time windows [17]. [PERSON] analyzed the resource and task constraints in the scheduling process of the GEO data relay satellite, and established the scheduling model of the GEO data relay satellite [18]. The current research lacks research on the overall resource allocation method for different types of nodes in the SIN.