Compared with the ground wireless communication, optical fiber, cable and other wired communication, satellite communication has the following characteristics：
1) Large coverage area, long communication distance. The communication cost has nothing to do with the communication distance.
The GEO satellite is about 35786 km away from the earth's surface, and a single satellite can cover more than 42% of the earth's surface. If three communication satellites are evenly distributed in the geostationary orbit, the global continuous communication can be realized except for the regions near the North Pole and the South Pole. A single satellite can cover all the users of a whole country. This is very important, especially for sparsely populated areas and marine areas, where the laying of ground network is either impossible or costly. In long-distance communication, satellite communication has more obvious advantages than microwave relay, cable, optical fiber and short wave wireless communication. For satellite communication, the cost of communication parties is independent of the distance between them. Moreover, thanks to the large coverage area of satellite communication, all those within this coverage are its potential users. This communication mode builds a platform to provide services at a reasonable price, and creates an important opportunity to compete with other means of communication in the market.
2) Flexible networking mode, multiple access connection ability, supporting complex network structure
Once the satellite is launched into the orbit, it can immediately provide services to a large number of users. The use of satellite communication can provide multimedia services for various users in a wide area more quickly than the ground network. Satellite communication mode is flexible and diverse, which can realize point to point, point to multi-point, multi-point to point and multi-point to multi-point communication modes. It doesn’t need the complex multicast protocol used in the ground network. With the multi beam ability of the communication satellite and on-board exchange and processing technology, multiple earth stations can flexibly network, support trunk transmission, television broadcasting, news collection, enterprise network communication and other services.
3) Safe and reliable, with low dependence on ground infrastructure
There are few links in the satellite communication system, and the radio wave mainly propagates in free space, so the stability and reliability of the link are high. At the same time, the position of communication satellite is much higher, making it less restricted by ground conditions. In the case of natural disasters and wars, satellite communication is a safe and reliable means of communication, sometimes even the only effective means of emergency communication.
4) Wide range of mobility
The implementation of satellite communication system is not limited by geographical conditions. Ground stations can be built in remote areas, islands, mountains, deserts, jungles and other complex terrain and landform areas, and can also be loaded on vehicles, aircrafts and ships. It can communicate both at rest and on the move. Within the coverage area of the satellite, mobile users can easily communicate with other fixed users or mobile users, thereby realizing the convenient information exchange anytime and anywhere. Therefore, satellite communication is widely used in the military field.
（Translated from Satellite Communication published by BEIJING INSTITUTE OF TECHNOLOGY PRESS）