# An Overview of Emergency Communication Networks
## 5 Sea Ad Hoc Network (SANET)
### Summary of Network Development Status
#### 3.2.2 Mobile Satellite Networks
According to the existing information, it is expected that the system will include a communication network of 60 artificial satellites by 2023. By 2025, the second phase will be completed, and a mobile satellite communication and network access system having space-air-ground-sea integration will be built. The Hongyun project is a \"star chain plan\" independently developed by China. It is expected that 156 satellites will be launched into orbit 1000 km above the ground. The project is committed to building a satellite-borne broadband global mobile Internet that can provide integrated services for communication, navigation, and remote sensing for all types of users around the world. Because of its extremely low communication delay, extremely high frequency reuse rate, and real global coverage, the Hongyun project can meet the needs of China, underdeveloped Internet areas, and large-scale user units to share broadband Internet access. At the same time, it can also meet the application requirements of high real-time information interaction, such as in emergency communication, sensor data acquisition, industrial Internet of Things, and remote control of unmanned equipment. The Tiantong-1 satellite mobile communication system is a satellite mobile communication system independently developed and constructed by China. It is also an important part of China's space information infrastructure, and solves the problem of seamless signal coverage in a particularly complex environment. The Tiantong-1 01, Tiantong-1 02, and Tiantong-1 03 satellites were successfully launched in 2016, 2020, and 2021 respectively. After the Tiantong-1 03 satellite was launched into orbit, it was networked in orbit to the Tiantong-1 01 and Tiantong-1 02 satellites. The Tiantong-1 satellite mobile communication system will achieve regional coverage in the Asia-Pacific region. It has the advantages of strong reliability, strong real-time performance, strong confidentiality, wide coverage, and long communication distance. It can provide stable and reliable voice, short message, video, and other mobile communication services, and improve the service level of satellite communication and emergency communication support capacity. The Tiantong-1 satellite system is a narrowband mobile satellite communication system. In case of natural disasters, the emergency communication capability of Tiantong-1 can play a significant role. The BeiDou, Tiantong, broadband satellite, and ground mobile communication systems can meet the transmission requirements for low delay, large capacity, and high rate of emergency communication. The network architecture is shown in Figure 9. After a disaster, the emergency command vehicle arrives at the disaster site, and realizes data communication and relay communication with the rear emergency command center through satellite communication, ground fixed cable communication, and ground mobile communication networks. If the vehicle cannot reach the site, rescuers will carry various emergency mobile communication terminals to the disaster site, and realize point-to-point communication with the emergency command vehicle through BeiDou handheld terminals, Beidou vehicle positioning terminals, short-wave radios, and Tiantong handhelds. The transmission route of emergency mobile communication is from the frontline personnel to the emergency communication vehicle, and then to the rear command center. If no public network exists, Ku broadband satellite communication is used to realize image transmission. Tiantonghandheld terminals are used to realize voice transmission and BeiDou short messages are used to realize text transmission of command and dispatch information. To summarize, Inmarsat, Iridium, and China's Tiantong-1 mobile satellite communication systems use 2G or 3G technology systems similar to land mobile communication systems. They also adopt FDMA/TDMA and CDMA multiple access mode, and support low-speed data and voice services.