At present, the continuous progress of information network technology has become the leading force of innovation driven development, which has a far-reaching impact on the political, military, economic, cultural and other fields, driving the reform and reconstruction of the social system. As an important information infrastructure supporting social development, ground-based information network and space-based information network have developed independently for a long time, and their limitations have become increasingly prominent. It is difficult to meet the needs of global network coverage, security, autonomy and controllability, and flexible access of all kinds of users. In recent years, the information network has been gradually integrated and developed. Relevant research has put forward the development vision of the space, earth and sea integrated information network [1~4] and the space, earth and sea integrated wireless communication network based on the sixth generation mobile communication technology (6g) [5]; The technical development idea of land, sea, air and space integrated information network has gradually become clear.
The land, sea, air and space integrated information network is an information infrastructure based on the ground network and extended by the space-based network, which covers natural space such as space, sky, land and sea, and provides information support for various activities of space-based, air-based, land-based, sea based and other users; Relevant research and development not only reflects a country's comprehensive scientific and technological and economic strength, but also an important support to promote China's independent innovation and development in major fields, meet national strategic needs, and enhance the competitiveness of national cyberspace.
The research difficulty of land, sea, air and space integrated information network technology is to use the network nodes based on satellite platform to build a space-based information network covering the world and realize the efficient and deep integration of land, sea, air and space networks. Therefore, this paper analyzes the construction needs, combs the development status, condenses the existing gaps, and puts forward the idea of integrated network architecture and development route suggestions, in order to provide reference for major planning and project implementation related to network power.
二、Demand analysis of land, sea, air and space integrated information network
China's information industry and its basic research have developed rapidly, but problems such as 'the earth is strong and the sky is weak' and 'the interior is strong and the exterior is weak' still exist. At present, space-based information networks mainly serve China's domestic regions, and overseas ground networks cannot support the application needs of diplomacy, emergency response and other aspects due to the lack of safe and controllable conditions. Therefore, the construction of land, sea, air and space integrated information networks is an important information basic guarantee to deal with the complex situation at home and abroad. In the civil field, the land, sea, air and space integrated information network needs to meet the needs of e-government, energy and water conservancy, production and manufacturing, marine economy, transportation, securities and finance, education and scientific research, cultural tourism, telemedicine and other industry applications and public applications.
（1） Global coverage and Earth Moon space extension capability
With the economic development and comprehensive strength enhancement of our country, the national strategic interests are significantly extended, and we need to have global activity capabilities in diplomacy, emergency and other aspects. In terms of information network, it is necessary to expand the scope of support from the traditional land and surrounding areas to the world, and expand the target of support from the traditional land users to maritime, space-based, space-based and other users; It is also necessary to further provide information service capabilities for lunar and deep space exploration.
（2） Multiple coverage capability of key and hot spots
In order to meet China's development and strategic deployment needs in key regions, the information network should cover East Asia, South Asia, countries / regions along the 'the Belt and Road' and the Arctic region as soon as possible. For hot spots, such as the South China Sea, we need to have multiple coverage capabilities and enhance support capabilities as needed. Compared with other regions covered by the world, the information network in key and hot areas should have stronger coverage capacity, more service users, higher data transmission bandwidth and better voice communication quality.
（3） Integrated networking capability
The land, sea, air and space integrated information network needs to ensure the communication needs of key users at any location and at any time in the world, and it needs to have the ability of space networking to achieve global random access and effective return of overseas information; It needs to have the multi network access capability of user terminals, support network users to access terrestrial Internet and mobile Internet services, and support the interoperability of mobile and broadband services.
（4） Space backbone transmission capacity
The ground backbone network has limited scalability to overseas, remote areas, sea areas and airspace, so it needs to have space backbone transmission capacity. At present, network users in China's civil fields mainly come from transportation, water conservancy, agriculture, local governments, overseas enterprises / media, mass commerce, etc; It is estimated that by 2025, the number of public users will be about 1 × 107, with about 3 industry users × 106, and the transmission demand of space backbone network is about 300 Gbps; It is estimated that by 2030, there will be about 3 public users × 107, with about 4 industry users × 106, and the transmission demand of space backbone network is about 1 TBPs. Only when the space backbone transmission capacity and the ground backbone network evolve synchronously and develop cooperatively can they meet the rapidly growing civil demand.
（5） Terminal diversification capability
In order to meet the needs of various scenarios, the land, sea, air and space integrated information network needs to be equipped with handheld, embedded, desktop and other diversified terminals. The handheld terminal should support a variety of communication systems, with navigation and positioning, voice communication, information transmission functions, and can be used as the main application terminal for disaster emergency treatment scenarios. Embedded terminals are generally used to provide ocean buoys and container monitoring units for space-based Internet of things services, which need to have the characteristics of multi-standard, miniaturization and low power consumption. Desktop terminals are divided into fixed, on-board, shipborne, airborne and other types, which need to have voice communication, data communication, video image transmission and other functions; As a network node, the ground LAN is connected to the space-based network to provide remote data transmission and broadband multimedia services.
3、 Development status of land, sea, air and space integrated information network
（1） Development status abroad
Since the 21st century, developed countries have been actively planning the construction of integrated information networks, competing for the control of space, air and sea by networks, and promoting the integration of space-based networks with ground-based Internet and mobile communication networks. At present, a number of space-based networks including synchronous orbit and LEO constellation have been formed [6] (see Table 1); Different systems have different emphasis on positioning and serving users, including civil systems such as Starlink and oneweb, military systems such as advanced extremely high frequency satellite communication system (AEHF), and integrated common systems such as iridium next.
Table 1 representative space-based information systems abroad
1. Information transmission
The inter satellite link technology tends to be mature, and the capacity continues to improve. For example, the Ka band link has been mature, and the laser link has entered the experimental stage. Developed countries are committed to developing land, sea, air and space integrated spatial information systems. For example, the United States has strengthened inter satellite links and on-board routing / switching capabilities, built a space communication network based on space multi satellite networking, and built a complete global information grid. Broadband satellite communication technology based on space networking is an important link in the development of land, sea, air and space integrated information network. It is of great significance to improve the communication capacity, coverage ability and survivability of broadband satellite communication system. Broadband satellite communication system is gradually developing towards Ka band multi beam, and the available bandwidth and capacity of the system are improved through frequency reuse, polarization multiplexing and other technologies.
The widely used network architecture mainly includes sky star earth network, space-based network, sky network earth network and other types. The skystar earth network architecture technology is relatively mature and widely used, but it is not suitable for application in China. Space based network architecture has advantages in security, invulnerability and independence, but due to its independent operation from the ground, it has increased the requirements for on-board processing and inter satellite information transmission capabilities, and it is difficult to fully promote and apply at the commercial level due to its high technical complexity and high system construction and maintenance costs. Through the cooperation of the space and ground networks, the space-based network architecture makes full use of the wide area coverage of the space-based network and the powerful transmission and processing capacity of the ground network, reducing the technical complexity and cost of the whole system.
3. Business classification
At present, space services are developing towards IP bearing, and single system shows a trend from single service to multi service. The evolving versions of broadband global satellite (WGS), iridium next and other systems gradually support diversified access services, and build support capabilities for real-time communication, space target monitoring, navigation and positioning and other services. The services provided by space-based networks and terrestrial networks also tend to be synchronized.
（2） Domestic development status
China is in the primary stage of promoting the comprehensive integration and development of space-based information network, future Internet and mobile communication network. In 2016, the major project of heaven earth integrated information network was listed in the outline of the 13th five year plan and the 13th five year plan for national scientific and technological innovation; In 2020, Satellite Internet was identified as one of the information infrastructures of 'new infrastructure construction'. Scientific research institutes and related enterprises have vigorously developed low earth orbit small satellite constellations, such as Hongyan constellation and Hongyun project, and the relevant test satellites have completed the verification of key technologies in orbit. While actively developing space-based networks, China continues to develop a new generation of high-throughput communication satellites, and has launched 'Shijian 13', 'Asia Pacific 6D' and 'Shijian 20', a new technology system test satellite; The coverage of high-throughput communication satellites to the ground is becoming more and more perfect, and the communication capacity is becoming larger and larger, which has gradually become an important expansion form of China's ground network infrastructure. The basic information of relevant space-based information systems is shown in Table 2.
Table 2 representative space-based information systems in China
4、 Analysis on the development gap of land, sea, air and space integrated information network in China
（1） The capacity of a single satellite is relatively small
Satellite capacity is an important indicator of satellite communication service quality, which determines the number of satellite service users and the communication capacity of a single user. The capacity of 'Asia Pacific 6D' satellite is 50 Gbps, which is 2.5 times that of 'Shijian 13', but it still lags far behind similar satellites in the United States. The capacity of viasat-2 broadband satellite in the United States is 300 Gbps, which is six times that of 'Asia Pacific 6D' satellite (its volume and weight are also several times that of 'Asia Pacific 6D' satellite). The viasat-3 satellite that the United States plans to launch in 2022 will further increase its capacity to 1 TBPs.
（2） There is no engineering application of space laser communication technology
Space laser communication has rich bandwidth resources, narrow beam divergence, low load quality and power consumption. It is an important means to achieve high-capacity transmission between satellite nodes and between satellite and ground nodes [9]. In recent years, China has made great progress in space laser communication technology, and has achieved high orbit to ground 5 Gbps communication rate test, reaching the world-class level; However, in the on orbit engineering application, there are many problems, such as the link cannot be connected, the amplifier is burnt out, the transmission rate is not up to standard, and it has not yet reached the state of stable use for a long time. The German European data relay system (EDRs) satellite realized the engineering application of high and low orbit inter satellite laser communication in 2016. The communication rate is 1.8 Gbps, and it still works normally [10].
（3） There is a clear gap between satellite production and mass deployment capabilities
The number of satellites in orbit is an important factor restricting the ability of land, sea, air and space integrated information network. Since the 1990s, the United States has deployed and operated 'iridium', 'global star' and other constellations, and is currently building Starlink constellations on a large scale, while China has no experience in the engineering construction and operation of large-scale constellations. Starlink and other emerging Satellite Internet projects adopt Internet thinking and learn from the concept of automobile manufacturing to significantly reduce production costs and improve satellite manufacturing capacity; The weekly output of satellites can reach 16, and the cost of each small satellite can be reduced to 500000 US dollars. In contrast, China still adopts the traditional engineering development mode for communication satellites. Even after the technology is mature, it will take two years of the whole satellite development cycle, and it does not have the ability of rapid and large-scale deployment.
（4） Space based networks are not systematic and difficult to integrate
China's existing communication satellites, relay satellites and broadband constellations under construction have all developed independently, and a unified standard system has not yet been formed. The technical systems of each system are different, making it difficult to achieve efficient connectivity between different network users. The development of space-based information networks and ground-based networks is uneven, and it is difficult to form a 'one network'. The integration of land, sea, air and space requires deep integration and development. In contrast, the United States proposed to integrate projects such as AEHF and ground grid based on TSAT system; Europe put forward the idea of building an integrated isicom information infrastructure and started early work. In 2018, the International Telecommunication Union (ITU) established the network 2030 focus group, taking satellite access as one of the characteristics of the future network; In 2019, the Institute of electrical and Electronics Engineers (IEEE) held the first global 6G wireless summit, which promoted the integration of space, space and space three-dimensional network coverage to become a common consensus in academic and engineering circles.
5、 Infrastructure of land, sea, air and space integrated information network
China urgently needs to build a 'global coverage, safe and controllable' information network. However, due to the basic national conditions, it is impossible to adopt the skystar earth network architecture to achieve information landing and interaction through the global construction of stations. Therefore, the land, sea, air and space integrated information network should adopt the network structure of sky and earth network, mainly including the core layer, access layer and user side (see Figure 1).
Figure 1 physical architecture of land, sea, air and space integrated information network
The core layer of land, sea, air and space integrated information network adopts the dual backbone architecture of heaven and earth. The ground-based part is composed of the traditional ground core network (such as ground optical fiber network, submarine optical fiber network, etc.) and the satellite ground station network, that is, the ground-based satellite ground network and the traditional core network integrated backbone network (hereinafter referred to as 'ground backbone'), which is the core part of the whole network, mainly realizing the functions of network control, resource management, protocol conversion, information processing, integration and sharing, and is responsible for the management, control and operation of the whole network. The space-based part refers to the space-based hybrid backbone network (hereinafter referred to as 'space backbone') composed of high orbit constellation, medium orbit constellation and low orbit constellation, which has certain access control, user management, information processing and service carrying capacity, provides broadband access, backbone interconnection, relay transmission, space-based measurement and control and other services, and can also expand the provision of navigation enhancement, satellite based monitoring and other services. The land, sea, air and space integrated information network has a wide range of cyberspace, covering the seabed, sea, land, air, near earth space, earth space, Earth Moon space, deep space, and the corresponding types of users are diverse. Using the double backbones of heaven and earth to build the core layer, build the 'one network of heaven and earth', give full play to the complementary advantages of heaven and earth network, and form an integrated information network core layer with integrated network architecture design, coordinated use of frequency resources, seamless integration of business applications, and collaborative guarantee of user services, which can effectively improve user access ability and heterogeneous network integration ability, and optimize system service efficiency.
The access layer of land, sea, air and space integrated information network is the expansion of the core layer, which is responsible for the access of users, including Earth Moon space extension network, space-based wireless private network, space-based wireless private network, sea based wireless private network, ground LAN, and mobile communication access network. ① The Earth Moon space extension network is an extension to provide Earth Moon space information services. It builds an all-time, large-scale, broadband and high-speed Earth Moon space communication network, provides all-day uninterrupted communication support, and realizes the efficient and reliable interaction of information between the earth and the moon; ② The space-based wireless private network is composed of multiple satellites or constellations. As the user network of the core layer, it undertakes the access of other types of users; ③ The space-based wireless private network is usually composed of aircraft, near space airships, unmanned aerial vehicles and other networks. As the user network of the core layer, it undertakes the access of other types of users; ④ Sea based wireless private network is usually composed of various surface ships, floating platforms and other networks. As the user network of the core layer, it undertakes the access of other users; ⑤ The combination of the ground LAN with the traditional ground core network and ground users in the ground backbone, that is, the ground Internet currently used; ⑥ The mobile communication access network is combined with the traditional ground core network and ground users in the ground backbone, that is, the ground mobile network currently used.
The dual backbone architecture of land, sea, air and space integrated information network, Earth Moon space extension network and other access layer networks are mainly applied to government, military, enterprises and other fields. According to the idea of 'network expansion and service extension', the functions of transmission networking, application services, security protection, operation and maintenance management and control are extended to the user end and integrated with the user application, forming a network that meets the requirements of ground, sea, air Space-based and other application systems with different user needs.
6、 Development Suggestions
（1） Strengthen the deep integration of network architecture, technical system and application service support system
① In terms of network architecture integration, it is suggested to break the closed development situation of traditional satellite and ground networks, and design an integrated multi-dimensional integrated common network from the three dimensions of logical function, function deployment and collaborative service, so that the network system components tend to be universal, the interface tends to be standardized, and the operation tends to be centralized. ② In terms of technology system integration, it is suggested to adopt a unified core network to support the co management and sharing mechanism of space-based Internet and ground mobile communication network, draw lessons from the 5g access network architecture design, and design an integrated air interface access technology system with variable parameter set according to the idea of software definition and high-low rail unification. ③ In terms of application service support system integration, it is suggested to adopt the design idea of cloud network integration, deploy space-based information port and lightweight space-based edge computing platform, and realize on orbit cloud edge collaborative processing; It integrates with the ground information port to provide an open, flat, efficient and wide area time sensitive application service support platform for various vertical industries and integrated applications.
（2） Promote the integration of communication, navigation, remote sensing and other systems, and establish a comprehensive spatial information network
The integration and application of various space service capabilities will help to improve the ability to deal with global emergencies and promote the development of space-based information commercialization service industry, which is the basis for supporting China to realize the right to control information. It is suggested to take 'one satellite multi-purpose, multi satellite networking, multi network integration, real-time service' as the goal, through the networking of cross series and cross constellation satellites and the deep integration with the ground network, based on the scientific and reasonable task planning of on-demand services and the mode of multi center collaborative services, to provide multi type, high-quality, stable, reliable, large-scale comprehensive services such as spatial data, communication, navigation, remote sensing, etc., to support the comprehensive applications of various industries.
（3） Promote the independent control of space-based network technology and the upgrading of high-end industries
The land, sea, air and space integrated information network is one of the important infrastructure for China to avoid being controlled by others and realize the network power. We should ensure that its design, development, construction and operation process is autonomous and controllable. It is suggested to reasonably maintain the investment in the independent research and development of the standard system in the fields of space-based traffic information management, perceptual network, space communication and so on, as well as the research and industrialization of basic equipment components, and change the current situation that standards depend on foreign countries, technologies rely on Introduction, and industries are restricted as soon as possible; Improve the level of localization and substitution in relevant application fields, stimulate domestic demand through product substitution and upgrading, and promote the circular development of the national economy.
（4） Strengthen the construction of system safety protection capacity
The land, sea, air and space integrated information network has the characteristics of exposed nodes, open channels, heterogeneous network interconnection, highly dynamic topology changes, limited on-board processing capacity, etc. in addition, it is vulnerable to external network attacks due to its integration with the Internet, especially in terms of measurement and control links, satellite ground networking, application service systems, and information supervision. It is suggested to strengthen the integrated design of communication and security protection according to the idea of 'system flexibility, security endogenous and dynamic empowerment'; New anti-interference waveform, spectrum cognitive radio, network authentication and access authentication, differentiated network security interconnection and isolation with multiple security levels, dynamic reconstruction of security protection equipment and other technologies are adopted to ensure the safety and reliability of the integrated network.
Source: Journal of Chinese Academy of Engineering