Satellite-Terrestrial Integration Has Become the General Trend
At present, with the gradual advancement of StarLink, Telesat, OneWeb and AST’s satellite constellation deployment plans, low-orbit satellite communications are on the rise again. The call for “merging” between satellite communications and terrestrial cellular communications is also getting louder. Chen Shanzhi believes that the main reasons for this are technological progress and changes in demand.
In terms of technology, one is the progress of satellite launch technology, including subversive technological innovations such as “one arrow with multiple satellites” and rocket recycling; the second is the progress of satellite manufacturing technology, including the progress of materials, power supply, and processing technology; the third is integrated circuit technology The advancement of satellites, miniaturization, modularization, and componentization of satellites, and the enhancement of on-board processing capabilities; the fourth is the advancement of communication technology. With the evolution of 3G, 4G, and 5G, large-scale antennas, millimeter wave With advances in shape and so on, terrestrial cellular mobile communication technology can also be applied to satellites.
On the demand side, with the expansion of industry applications and human activities, the advantages of satellite communication global coverage and space coverage are beginning to emerge. As of today, the terrestrial mobile communication system has covered more than 70% of the population, but due to technical and economic factors, it only covers 20% of the land area, which is only about 6% based on the earth’s surface area. With the development of the industry, aviation, ocean, fishery, petroleum, environmental monitoring, outdoor off-road activities, as well as national strategy and military communications, etc., have strong demand for wide-area and space coverage.
Chen Shanzhi believes that the direct connection of mobile phones to satellites means that satellite communications will enter the consumer market from the industry application market. “However, it is ridiculous to say that Starlink can replace or even subvert 5G.” Chen Shanzhi pointed out that satellite communication has many limitations. The first is the invalid coverage of the area. Three high-orbit synchronous satellites can cover the whole world. Hundreds of low-orbit satellites move at high speed relative to the ground and can only cover evenly. Many areas are invalid because there are actually no users. ; Second, satellite signals cannot cover indoors and outdoors covered by overpasses and mountain forests; third, the miniaturization of satellite terminals and the contradiction between antennas, especially people have become accustomed to the built-in antennas of ordinary mobile phones (users have no sense), The current commercial satellite mobile phone still has an external antenna; fourth, the spectral efficiency of satellite communication is much lower than that of cellular mobile communication. Spectrum efficiency is above 10 bit/s/Hz. Finally, and most importantly, because it involves many links such as satellite manufacturing, satellite launch, ground equipment, satellite operation and service, the construction and operation and maintenance cost of each communication satellite is ten times or even hundreds of times that of a ground base station, so the communication fee will definitely increase. Higher than 5G terrestrial cellular communications.
Compared with the terrestrial cellular mobile communication system, the main technical differences and challenges of the satellite communication system are as follows: 1) The propagation characteristics of the satellite channel and the terrestrial channel are different, the satellite communication has a long propagation distance, the signal propagation path loss is large, and the transmission delay is large. Bringing challenges to link budget, timing relationship and transmission scheme; 2) High-speed satellite movement, causing time synchronization tracking performance, frequency synchronization tracking (Doppler effect), mobility management (frequent beam switching and inter-satellite switching), modulation Demodulation performance and other challenges. For example, a mobile phone is only a few hundred meters to a kilometer level from a ground base station, and 5G can support a terminal movement speed of 500km/h; while a low-orbit satellite is about 300 to 1,500km away from a ground mobile phone, and the satellite moves at a speed of about 7.7 to 7.1km/s relative to the ground, exceeding 25,000km /h.