# An Overview of Emergency Communication Networks
## 3 Review of Emergency Communication Networks
### Network Classification
#### 3.1.1 Satellite Networks  
Satellite communication technology is a method of communication between two or more Earth stations using artificial Earth satellites as relay stations to forward radio waves. Satellite communication systems are usually classified according to the satellite orbit altitude, and can be divided into geosynchronous Earth orbit (GEO) satellites, medium Earth orbit (MEO) satellites, and low Earth orbit (LEO) satellites. The characteristics of different satellite communication systems are shown in Table 1.  
GEO satellites cover a wide range, with a single satellite covering up to 42% of the Earth's area. GEO satellite mobile communication systems include the North American satellite mobile communication system (MSAT) and the International Maritime Satellite (Inmarsat) system. At present, GEO satellites are being developed towards the direction of high throughput, which can improve the utilization rate of the satellite frequency and data throughput by utilizing the rich spectrum resources of the Ka band and frequency reuse technology. MEO satellites cover a much smaller area than GEO satellites, and are mainly used to provide satellite Internet access services with high bandwidth, low cost, and low delay. MEO satellite mobile communication systems mainly include Immarsat-P, Odyssey, MAGSS-14, and BeiDou positioning system. LEO satellites have low cost and small coverage per satellite. The current development trend of the LEO satellite is for miniaturization, low cost, and more intensive networking. Miniaturization and lightweight design can reduce the manufacturing and transmission costs, provide greater system throughput through intensive networking, and dynamically allocate the power and bandwidth to each beam using beam forming and beam shaping functions, so as to maximize the performance and reduce the interference in high orbit satellites. The satellite communication system is mainly composed of space, ground, and user segments, as shown in Figure 1. Space segment: with communication satellites as the main body, used for receiving and forwarding signals from satellite communication Earth stations, to achieve communication between Earth stations or between Earth stations and spacecraft. Ground segment: including satellite transponder, gateway station, Satellite Control Center (SCC), and Tracking, Telemetry, and Command station (TT&C), to realize communication between users. User segment: mainly composed of various terminal user devices, including Very Small Antenna Terminal (VSAT) stations, handheld terminals, and mobile terminals mounted on cars, ships, and planes, as well as various applications and services based on satellite communication. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **GEO Satellite** & **MEO Satellite** & **LEO Satellite** \\ \hline Track height & 35,800 km & 2000–20,000 km & 500–2000 km \\ System communication capacity & 50 Gpbs & 16 Gpbs & 350 Tbps \\ End-to-end delay & 500 ms & 150 ms & 30 ms \\ System capacity density & 23.24 bps/km\({}^{2}\) & 26.14 bps/km\({}^{2}\) & 17 Mbps/km\({}^{2}\) \\ Capacity cost & \$60 million/Gbit & \$13.75 million/Gbit & \$18,400/Gbit \\ Satellite life & 10–15 years & 10–15 years & 3–7 years \\ Technical risk & medium & low & high \\ \hline \end{tabular}
\end{table} 
Table 1: Characteristics of satellite communication system. With the development of satellite communication technology, Earth observation satellite remote sensing technology has been extended. This technology uses the visible light, infrared, and microwave sensors built on satellites to detect and identify the Earth's resources and environmental information by collecting the electromagnetic radiation data of the Earth's surface and near-Earth space. At present, this technology has been widely used in many fields, such as land natural resources surveys, marine ecological environment protection, and meteorological disaster prediction.