# An Overview of Emergency Communication Networks
## 5 Sea Ad Hoc Network (SANET)
### Future Development Directions
#### 3.4.2 Space-Air-Ground-Sea Integration Networks  
Due to limitations in the radio spectrum, service geographic coverage, and operating costs, 5G ground communication networks alone cannot provide high-quality and reliable services at any time and in any place. This is especially the case in remote areas such as oceans, forests, and deserts [114]. In order to provide truly ubiquitous wireless communication services on a global scale, it is necessary to develop an integrated space-air-ground-sea network to achieve global connectivity. The rapid development of wireless, broadband, fusion, and three-dimensional network technology provides the construction foundation for the integration of the space-air-ground-sea network with information sharing, interconnection, and unified command. Integrated use of big data, cloud computing, AI, satellite communications, multimedia communications, mobile communications, and other advanced technologies, and integration of space-based, air-based, ground-based, and sea-based platforms, can be used to construct the space-air-ground-sea integrated emergency communication network architecture. This architecture can realize the overall emergency resource planning and collaborative services of multiple platforms. The network architecture is shown in Figure 12. The integrated space-air-ground-sea network is based on a ground network, extended by air-based and sea-based networks, and connected and supplemented by a space-based network; thus, it covers the natural space including space, the sky, the ground, and the ocean [126; 127]. The air-based network consists of satellites, which can be divided into GEO, MEO, and LEO satellites. The space-based network is composed of aerial platforms such as near-space airships, airplanes, UAVs, and hot-air balloons. The ground-based network is mainly composed of LANs and cellular mobile networks, including all wired and wireless network facilities on the ground. Currently, this mainly relies on 5G network technology. The sea-based network consists of coastal base stations, surface ships, buoys, etc. Figure 12: System topology of the space-air-ground-sea integrated emergency communication network. The air-based network is a satellite network that is composed of multiple satellites in different orbits with different types and levels of performance, which form a constellation covering the whole world. It provides information interaction for users, aircraft, and various communication platforms on the ground and in the air through inter-satellite and satellite-Earth links. The network can be divided into GEO, MEO, and LEO satellite systems. GEO satellites have a large single satellite coverage capability, but high deployment cost and long propagation delay. In contrast, LEO satellites, having small single satellite coverage but low cost and small propagation delay, have gradually become the object of consideration. Giant constellation systems composed of LEO satellites are the focus of current research, and include Starlink and OneWeb. China also has plans for the launch of corresponding constellations, such as \"Hongyun\" and \"Hongyan\", which are introduced in Section 3.2.2. Space-based network  
Space-based networks can be divided into low-space networks and high-space networks. Low-space networks are mainly composed of UAVs, and also involve tethering UAVs, low-altitude balloons, tethered balloons, etc. High-space networks consist of balloons, airships, and gliders. Space-based communication approaches can significantly expand the communication distance, extend the coverage of the ground network, and complete the forwarding and exchange of information in the air. The altitude of a low-space network is no more than 10 km, which is not suitable for disasters such as storms or hurricanes. UAV technology involves a flying base station that can be used to access disaster-affected areas, efficiently obtain the required data, and understand the disaster situation.