Classification of satellite communication systems

Work track

According to the work track, satellite communication systems generally fall into the following three categories:

1. Low Earth Orbit Satellite Communication System (LEO):

From the ground 500-2000Km, transmission delay and power consumption are relatively small, but the coverage of each star is also relatively small, typical systems have Motorola's comet system. Low-orbit satellite communication systems can support multi-hop communication due to their low satellite orbits and short signal propagation delays. Their low link loss can reduce the requirements for satellites and user terminals. Microsatellite/small satellites and handheld user terminals can be used. But low-orbit satellite systems also pay a lot for these advantages: Because of the low orbit, each satellite can cover a relatively small area, and it takes dozens of satellites to form a global system. For instance, the satellite system has 66 satellites. Globalstar has 48 satellites and Teledisc has 288 satellites. At the same time, due to the fast movement of low-orbiting satellites, for a single user, the time from when the satellite rises from the horizon to falling below the horizon is shorter, so inter-satellite or inter-carrier switching is frequent. Therefore, the low-rail system has a relatively complex system configuration and control, high technology risks, and a relatively high construction cost.

2. Medium-Orbit Satellite Communication System (MEO):

From the ground 2000-20000Km, the transmission delay is greater than the low-orbit satellites, but the coverage is also larger, the typical system is the international maritime satellite system. The medium-orbit satellite communication system can be said to be a compromise between the geostationary satellite system and the low-orbit satellite system. The medium-orbit satellite system combines the advantages of these two schemes, and at the same time overcomes the inadequacies of the two schemes to some extent. The orbit loss and propagation delay of medium-earth orbit satellites are relatively small, and simple small satellites can still be used. If both the medium-orbit and low-orbit satellite systems use inter-satellite links, when the user performs long-distance communication, the time delay of the middle orbit system information through the satellite inter-satellite link sub-network will be lower than that of the low-orbit system. And because its orbit is much higher than that of low-orbit satellite systems, each satellite can cover a much larger range than a low-orbit system. When the orbit height is l0000Km, each satellite can cover 23.5% of the earth's surface, so long as Several satellites can cover the globe. If there are more than a dozen satellites, it can provide double coverage for most of the world, so that diversity can be used to improve the reliability of the system, while the system investment is lower than that of low-orbit systems. Therefore, in a certain sense, the China Railway System may be a superior solution for establishing a global or regional satellite mobile communication system. Of course, if it is necessary to provide broadband services for terrestrial terminals, there will be difficulties in the mid-orbit system, and the use of low-orbit satellite systems as a high-speed multimedia satellite communication system will outperform the medium-orbit satellite system.

3. High Earth Orbit Satellite Communication System (GEO):

35800km from the ground, that is, synchronous geostationary orbit. In theory, global coverage can be achieved with three high orbit satellites. The technology of traditional synchronous orbit satellite communication systems is the most mature. Since the use of synchronous satellites in communication services, the establishment of global satellite communication systems using geostationary satellites has become a traditional model for establishing satellite communication systems. However, synchronous satellites have an insurmountable obstacle, that is, a long propagation delay and a large link loss, which seriously affect its application in certain communication fields, especially in satellite mobile communication applications. First, the geostationary satellite orbit is high, the link loss is large, and the user terminal receiver performance requirements are high. This kind of system is difficult to support the handset to communicate directly through satellites, or it needs to use a satellite antenna (L-band) of more than l2m, which puts higher requirements on satellite satellite-borne communication payload, which is not conducive to small-satellite technology on the move. Use in communications. Secondly, due to the long link length and large propagation delay, the propagation delay of single-hop will reach several hundred milliseconds. With the processing time of the speech encoder, the single-hop delay will further increase when the mobile user conducts the satellite. When the two-hop communication is performed, the delay may even reach the second level, which is unbearable to users, especially voice communication users. In order to avoid such double-hop communication, satellite processing must be adopted to make the satellites have switching functions, but this will inevitably increase the complexity of the satellites, which not only increases the system cost but also has certain technical risks.

At present, the synchronous orbit satellite communication system is mainly used for VSAT systems, television signal forwarding, etc., and is less used for personal communication.

Communication range

According to the communication range, satellite communication systems can be divided into international communication satellites, regional communication satellites, and domestic communication satellites.

Usage distinction

According to the purpose of use, satellite communication systems can be divided into integrated service communication satellites, military communication satellites, maritime communication satellites, and live-TV satellites.

Forwarding capability

According to the forwarding capability, satellite communication systems can be divided into satellites without satellite processing capabilities and satellites with satellite processing capabilities.